WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xiIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . .

xiv

1. Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

2. Normative references. . . . . . . . . . . . . . . . . . . . . . .

3. Terms, definitions, and symbols
4. Conformance2. . . . . . . . . . . . . . . . . . .

3. . . . . . . . . . . . . . . . . . . . . . . . . .

7

5. Environment. . . . . . . . . . .
5.1 Conceptual models. . . . . .
5.1.1
Translation environment .
5.1.2
Execution environments.
5.2 Environmental considerations. .
5.2.1 Character sets
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5.2.2
Character display semantics
5.2.3 Signals and interrupts . .
5.2.4
Environmental limits
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6. Language . . . . . . . . . . . . . . . . .
6.1 Notation . . . . . . . . . . . . . . .
6.2 Concepts. . . . . . . . . . . . . .
6.2.1 Scopes of identifiers. . . . . .
6.2.2
Linkages of identifiers . . . . . .
6.2.3 Name spaces of identifiers. . . .
6.2.4 Storage durations of objects. . .
6.2.5 Types. . . . . . . . . . . .
6.2.6 Representations of types . . . . .
6.2.7 Compatible type and composite type
6.3 Conversions. . . . . . . . . . . . .
6.3.1 Arithmetic operands. . . . . .
6.3.2 Other operands. . . . . . . .
6.4 Lexical elements. . . . . . . . . . .
6.4.1 Keywords . . . . . . . . . . .
6.4.2 Identifiers . . . . . . . . . . .
6.4.3 Universal character names. . . .
6.4.4
Constants . . . . . . . . . . .
6.4.5 String literals. . . . . . . . .
6.4.6Punctuators . . . . . . . . . .
6.4.7 Header names. . . . . . . . .
6.4.8 Preprocessing numbers. . . . .
6.4.9 Comments. . . . . . . . . .
6.5 Expressions. . . . . . . . . . . . .

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iii

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

6.5.1
Primary expressions. . .
6.5.2 Postfix operators . . . . .
6.5.3
Unary operators. . . . .
6.5.4 Cast operators . . . . . .
6.5.5
Multiplicative operators. .
6.5.6 Additive operators. . . .
6.5.7 Bitwise shift operators . . .
6.5.8
Relational operators . . . .
6.5.9 Equality operators. . . .
6.5.10 Bitwise AND operator . . .
6.5.11 Bitwise exclusive OR operator
6.5.12 Bitwise inclusive OR operator
6.5.13 Logical AND operator . . .
6.5.14 Logical OR operator. . .
6.5.15 Conditional operator. . .
6.5.16 Assignment operators . . .
6.5.17 Comma operator . . . . .
6.6 Constant expressions . . . . . . .
6.7 Declarations. . . . . . . . . .
6.7.1 Storage-class specifiers
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6.7.2
Type specifiers . . . . . .
6.7.3 Type qualifiers . . . . . .
6.7.4
Function specifiers. . . .
6.7.5 Declarators. . . . . . .
6.7.6 Type names . . . . . . .
6.7.7Type definitions. . . . .
6.7.8 Initialization. . . . . .
6.8 Statements and blocks. . . . . .
6.8.1
Labeled statements. . . .
6.8.2 Compound statement. . .
6.8.3 Expression and null statements
6.8.4 Selection statements. . .
6.8.5 Iteration statements . . . .
6.8.6 Jump statements. . . . .
6.9 External definitions. . . . . . .
6.9.1
Function definitions . . . .
6.9.2 External object definitions.
6.10 Preprocessing directives. . . . .
6.10.1 Conditional inclusion. . .
6.10.2 Source file inclusion. . .
6.10.3 Macro replacement . . . .
6.10.4 Line control . . . . . . .
6.10.5 Error directive . . . . . .
6.10.6 Pragma directive . . . . .
iv

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WG14/N1256

Committee Draft — Septermber 7, 2007

6.10.7 Null directive. . . . .
6.10.8 Predefined macro names .
6.10.9 Pragma operator. . . .
6.11 Future language directions. . .
6.11.1 Floating types. . . . .
6.11.2 Linkages of identifiers . .
6.11.3 External names. . . .
6.11.4 Character escape sequences
6.11.5 Storage-class specifiers.
6.11.6 Function declarators. .
6.11.7 Function definitions . . .
6.11.8 Pragma directives. . .
6.11.9 Predefined macro names .

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7. Library . . . . . . . . . . . . . . . . . . . . .
7.1 Introduction. . . . . . . . . . . . . . . .
7.1.1 Definitions of terms . . . . . . . . . .
7.1.2 Standard headers . . . . . . . . . . .
7.1.3 Reserved identifiers . . . . . . . . . .
7.1.4
Use of library functions. . . . . . . .
7.2 Diagnostics <assert.h>. . . . . . . . . .
7.2.1 Program diagnostics. . . . . . . . .
7.3 Complex arithmetic <complex.h>. . . . . .
7.3.1
Introduction . . . . . . . . . . . . .
7.3.2
Conventions . . . . . . . . . . . . .
7.3.3 Branch cuts . . . . . . . . . . . . .
7.3.4 The CX_LIMITED_RANGE pragma
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7.3.5
Trigonometric functions . . . . . . . .
7.3.6
Hyperbolic functions. . . . . . . . .
7.3.7 Exponential and logarithmic functions
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7.3.8
Power and absolute-value functions
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7.3.9
Manipulation functions. . . . . . . .
7.4 Character handling <ctype.h> . . . . . . . .
7.4.1
Character classification functions. . . .
7.4.2 Character case mapping functions. . . .
7.5 Errors <errno.h>. . . . . . . . . . . . .
7.6 Floating-point environment <fenv.h>. . . . .
7.6.1 The FENV_ACCESS pragma. . . . . .
7.6.2 Floating-point exceptions. . . . . . .
7.6.3 Rounding . . . . . . . . . . . . . .
7.6.4 Environment. . . . . . . . . . . .
7.7 Characteristics of floating types <float.h> . . .
7.8 Format conversion of integer types <inttypes.h>
7.8.1
Macros for format specifiers. . . . . .
7.8.2 Functions for greatest-width integer types
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ISO/IEC 9899:TC3v

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

7.9 Alternative spellings <iso646.h> . . . . . . . . . . .
7.10 Sizes of integer types <limits.h>. . . . . . . . . .
7.11 Localization <locale.h> . . . . . . . . . . . . . .
7.11.1 Locale control . . . . . . . . . . . . . . . .
7.11.2 Numeric formatting convention inquiry . . . . . .
7.12 Mathematics <math.h> . . . . . . . . . . . . . . .
7.12.1 Treatment of error conditions . . . . . . . . . .
7.12.2 The FP_CONTRACT pragma. . . . . . . . . .
7.12.3 Classification macros. . . . . . . . . . . . .
7.12.4 Trigonometric functions . . . . . . . . . . . .
7.12.5 Hyperbolic functions. . . . . . . . . . . . .
7.12.6 Exponential and logarithmic functions. . . . . .
7.12.7 Power and absolute-value functions. . . . . . .
7.12.8 Error and gamma functions . . . . . . . . . . .
7.12.9 Nearest integer functions . . . . . . . . . . . .
7.12.10 Remainder functions. . . . . . . . . . . . .
7.12.11 Manipulation functions. . . . . . . . . . . .
7.12.12 Maximum, minimum, and positive difference functions
7.12.13 Floating multiply-add . . . . . . . . . . . . .
7.12.14 Comparison macros . . . . . . . . . . . . . .
7.13 Nonlocal jumps <setjmp.h>. . . . . . . . . . . .
7.13.1 Save calling environment. . . . . . . . . . .
7.13.2 Restore calling environment. . . . . . . . . .
7.14 Signal handling <signal.h> . . . . . . . . . . . . .
7.14.1 Specify signal handling. . . . . . . . . . . .
7.14.2 Send signal. . . . . . . . . . . . . . . . .
7.15 Variable arguments <stdarg.h>. . . . . . . . . . .
7.15.1 Variable argument list access macros . . . . . . .
7.16 Boolean type and values <stdbool.h>. . . . . . . .
7.17 Common definitions <stddef.h> . . . . . . . . . . .
7.18 Integer types <stdint.h> . . . . . . . . . . . . . .
7.18.1 Integer types. . . . . . . . . . . . . . . .
7.18.2 Limits of specified-width integer types. . . . . .
7.18.3 Limits of other integer types. . . . . . . . . .
7.18.4 Macros for integer constants. . . . . . . . . .
7.19 Input/output <stdio.h>. . . . . . . . . . . . . .
7.19.1 Introduction . . . . . . . . . . . . . . . . .
7.19.2 Streams. . . . . . . . . . . . . . . . . .
7.19.3 Files . . . . . . . . . . . . . . . . . . . .
7.19.4 Operations on files. . . . . . . . . . . . . .
7.19.5 File access functions. . . . . . . . . . . . .
7.19.6 Formatted input/output functions. . . . . . . .
7.19.7 Character input/output functions . . . . . . . . .
7.19.8 Direct input/output functions. . . . . . . . . .
vi

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WG14/N1256

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202
203
204
205
206
212
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215
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235
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238
239
240
243
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257
259
260
262
262
264
266
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270
274
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WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

7.19.9 File positioning functions. . . . . . . . . . . .
7.19.10 Error-handling functions . . . . . . . . . . . . .
7.20 General utilities <stdlib.h>. . . . . . . . . . . . .
7.20.1 Numeric conversion functions . . . . . . . . . . .
7.20.2 Pseudo-random sequence generation functions. . . .
7.20.3 Memory management functions . . . . . . . . . .
7.20.4 Communication with the environment. . . . . . .
7.20.5 Searching and sorting utilities . . . . . . . . . . .
7.20.6 Integer arithmetic functions. . . . . . . . . . .
7.20.7 Multibyte/wide character conversion functions. . . .
7.20.8 Multibyte/wide string conversion functions. . . . .
7.21 String handling <string.h> . . . . . . . . . . . . . .
7.21.1 String function conventions . . . . . . . . . . . .
7.21.2 Copying functions. . . . . . . . . . . . . . .
7.21.3 Concatenation functions . . . . . . . . . . . . .
7.21.4 Comparison functions . . . . . . . . . . . . . .
7.21.5 Search functions. . . . . . . . . . . . . . . .
7.21.6 Miscellaneous functions . . . . . . . . . . . . .
7.22 Type-generic math <tgmath.h>. . . . . . . . . . . .
7.23 Date and time <time.h>. . . . . . . . . . . . . . .
7.23.1 Components of time
. . . . . . . . . . . . . .
7.23.2 Time manipulation functions. . . . . . . . . . .
7.23.3 Time conversion functions. . . . . . . . . . . .
7.24 Extended multibyte and wide character utilities <wchar.h> . .
7.24.1 Introduction . . . . . . . . . . . . . . . . . .
7.24.2 Formatted wide character input/output functions. . .
7.24.3 Wide character input/output functions. . . . . . .
7.24.4 General wide string utilities. . . . . . . . . . .
7.24.5 Wide character time conversion functions. . . . . .
7.24.6 Extended multibyte/wide character conversion utilities .
7.25 Wide character classification and mapping utilities <wctype.h>
7.25.1 Introduction . . . . . . . . . . . . . . . . . .
7.25.2 Wide character classification utilities . . . . . . . .
7.25.3 Wide character case mapping utilities . . . . . . . .
7.26 Future library directions. . . . . . . . . . . . . . . .
7.26.1 Complex arithmetic <complex.h> . . . . . . . .
7.26.2 Character handling <ctype.h>. . . . . . . . .
7.26.3 Errors <errno.h>. . . . . . . . . . . . . .
7.26.4 Format conversion of integer types <inttypes.h>.
7.26.5 Localization <locale.h>. . . . . . . . . . .
7.26.6 Signal handling <signal.h>. . . . . . . . . .
7.26.7 Boolean type and values <stdbool.h>. . . . . .
7.26.8 Integer types <stdint.h>. . . . . . . . . . .
7.26.9 Input/output <stdio.h>. . . . . . . . . . . .
Contents

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302
304
306
307
312
313
315
318
320
321
323
325
325
325
327
328
330
333
335
338
338
339
341
348
348
349
367
371
385
386
393
393
394
399
401
401
401
401
401
401
401
401
401
402
vii

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

WG14/N1256

7.26.10 General utilities <stdlib.h>. . . . . . .
7.26.11 String handling <string.h>. . . . . . .
7.26.12 Extended multibyte and wide character utilities<wchar.h>. . . . . . . . . . . . . .
7.26.13 Wide character classification and mapping utilities<wctype.h> . . . . . . . . . . . . . .
Annex A (informative) Language syntax summary. .
A.1 Lexical grammar. . . . . . . . . . . .
A.2 Phrase structure grammar . . . . . . . . .
A.3 Preprocessing directives. . . . . . . . .

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403
403
409
416

Annex B (informative) Library summary. . . . . . . . . . . . .
B.1 Diagnostics <assert.h>. . . . . . . . . . . . . . .
B.2 Complex <complex.h> . . . . . . . . . . . . . . . .
B.3 Character handling <ctype.h> . . . . . . . . . . . . .
B.4 Errors <errno.h>. . . . . . . . . . . . . . . . . .
B.5 Floating-point environment <fenv.h>. . . . . . . . . .
B.6 Characteristics of floating types <float.h> . . . . . . . .
B.7 Format conversion of integer types <inttypes.h> . . . . .
B.8 Alternative spellings <iso646.h> . . . . . . . . . . . .
B.9 Sizes of integer types <limits.h>. . . . . . . . . . .
B.10 Localization <locale.h> . . . . . . . . . . . . . . .
B.11 Mathematics <math.h> . . . . . . . . . . . . . . . .
B.12 Nonlocal jumps <setjmp.h>. . . . . . . . . . . . .
B.13 Signal handling <signal.h> . . . . . . . . . . . . . .
B.14 Variable arguments <stdarg.h>. . . . . . . . . . . .
B.15 Boolean type and values <stdbool.h>. . . . . . . . .
B.16 Common definitions <stddef.h> . . . . . . . . . . . .
B.17 Integer types <stdint.h> . . . . . . . . . . . . . . .
B.18 Input/output <stdio.h>. . . . . . . . . . . . . . .
B.19 General utilities <stdlib.h>. . . . . . . . . . . . .
B.20 String handling <string.h> . . . . . . . . . . . . . .
B.21 Type-generic math <tgmath.h>. . . . . . . . . . . .
B.22 Date and time <time.h>. . . . . . . . . . . . . . .
B.23 Extended multibyte/wide character utilities <wchar.h>. . .
B.24 Wide character classification and mapping utilities <wctype.h>

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419
419
419
421
421
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428
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429
431
433
434
434
435
437

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. . . . . . . . . . . . . . . . . 439

Annex D (normative) Universal character names for identifiers
Annex E (informative) Implementation limits

Contents. . . . . . . 440. . . . . . . . . . . . . . 442

Annex F (normative) IEC 60559 floating-point arithmetic
F.1 Introduction. . . . . . . . . . . . . .
F.2 Types . . . . . . . . . . . . . . . . .
F.3 Operators and functions. . . . . . . . .
viii

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Annex C (informative) Sequence points

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444
444
444
445

WG14/N1256

F.4
F.5
F.6
F.7
F.8
F.9

Committee Draft — Septermber 7, 2007

Floating to integer conversion
Binary-decimal conversion
Contracted expressions . .
Floating-point environment
Optimization . . . . . .
Mathematics <math.h> .

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447
447
448
448
451
454

Annex G (informative) IEC 60559-compatible complex arithmetic
G.1 Introduction. . . . . . . . . . . . . . . . . .
G.2 Types . . . . . . . . . . . . . . . . . . . . .
G.3 Conventions. . . . . . . . . . . . . . . . . .
G.4 Conversions. . . . . . . . . . . . . . . . . .
G.5 Binary operators. . . . . . . . . . . . . . . .
G.6 Complex arithmetic <complex.h>. . . . . . . .
G.7 Type-generic math <tgmath.h>. . . . . . . . .

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467
467
467
467
468
468
472
480

Annex H (informative) Language independent arithmetic
H.1 Introduction. . . . . . . . . . . . . .
H.2 Types . . . . . . . . . . . . . . . . .
H.3 Notification. . . . . . . . . . . . . .

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481
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485

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ISO/IEC 9899:TC3

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Annex I (informative) Common warnings. . . . . . . . . . . . . . . . 487

Annex J (informative) Portability issues .
J.1 Unspecified behavior . . . . .
J.2 Undefined behavior. . . . .
J.3 Implementation-defined behavior
J.4 Locale-specific behavior. . .
J.5 Common extensions. . . . .

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Bibliography
Index

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489
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512
513

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Contentsix

ISO/IEC 9899:TC3x

Committee Draft — Septermber 7, 2007

Contents

WG14/N1256

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

Foreword
1

ISO (the International Organization for Standardization) and IEC (the International
Electrotechnical Commission) form the specialized system for worldwide
standardization. National bodies that are member of ISO or IEC participate in thedevelopment of International Standards through technical committees established by therespective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other internationalorganizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.

2

International Standards are drafted in accordance with the rules given in the ISO/IEC
Directives, Part 3.

3

In the field of information technology, ISO and IEC have established a joint technicalcommittee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technicalcommittee are circulated to national bodies for voting. Publication as an International
Standard requires approval by at least 75% of the national bodies casting a vote.

4International Standard ISO/IEC 9899 was prepared by Joint Technical Committee
ISO/IEC JTC 1, Information technology, Subcommittee SC 22, Programming languages,
their environments and system software interfaces. The Working Group responsible forthis standard (WG 14) maintains a site on the World Wide Web at
http://www.open-std.org/JTC1/SC22/WG14/
containing
additional
information relevant to this standard such as a Rationale for many of the decisions madeduring its preparation and a log of Defect Reports and Responses.

5This second edition cancels and replaces the first edition, ISO/IEC 9899:1990, as
amended and corrected by ISO/IEC 9899/COR1:1994, ISO/IEC 9899/AMD1:1995, andISO/IEC 9899/COR2:1996. Major changes from the previous edition include:— restricted character set support via digraphs and <iso646.h> (originally specified
in AMD1)— wide character library support in <wchar.h> and <wctype.h> (originallyspecified in AMD1)— more precise aliasing rules via effective type— restricted pointers— variable length arrays— flexible array members— static and type qualifiers in parameter array declarators— complex (and imaginary) support in <complex.h>— type-generic math macros in <tgmath.h>— the long long int type and library functions
Forewordxi

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

WG14/N1256— increased minimum translation limits— additional floating-point characteristics in <float.h>— remove implicit int— reliable integer division— universal character names (\u and \U)— extended identifiers— hexadecimal floating-point constants and %a and %A printf/scanf conversion
specifiers— compound literals— designated initializers— // comments— extended integer types and library functions in <inttypes.h> and <stdint.h>— remove implicit function declaration— preprocessor arithmetic done in intmax_t/uintmax_t— mixed declarations and code
— new block scopes for selection and iteration statements— integer constant type rules— integer promotion rules— macros with a variable number of arguments— the vscanf family of functions in <stdio.h> and <wchar.h>— additional math library functions in <math.h>— treatment of error conditions by math library functions (math_errhandling)— floating-point environment access in <fenv.h>— IEC 60559 (also known as IEC 559 or IEEE arithmetic) support— trailing comma allowed in enum declaration— %lf conversion specifier allowed in printf— inline functions— the snprintf family of functions in <stdio.h>— boolean type in <stdbool.h>— idempotent type qualifiers— empty macro arguments

xii

ForewordWG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3— new structure type compatibility rules (tag compatibility)— additional predefined macro names— _Pragma preprocessing operator— standard pragmas— _ _func_ _ predefined identifier— va_copy macro— additional strftime conversion specifiers— LIA compatibility annex— deprecate ungetc at the beginning of a binary file— remove deprecation of aliased array parameters— conversion of array to pointer not limited to lvalues— relaxed constraints on aggregate and union initialization— relaxed restrictions on portable header names— return without expression not permitted in function that returns a value (and viceversa)
6

Annexes D and F form a normative part of this standard; annexes A, B, C, E, G, H, I, J,
the bibliography, and the index are for information only. In accordance with Part 3 of the
ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples arealso for information only.

Forewordxiii

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

WG14/N1256

Introduction
1

With the introduction of new devices and extended character sets, new features may be
added to this International Standard. Subclauses in the language and library clauses warn
implementors and programmers of usages which, though valid in themselves, may
conflict with future additions.

2

Certain features are obsolescent, which means that they may be considered forwithdrawal in future revisions of this International Standard. They are retained becauseof their widespread use, but their use in new implementations (for implementation
features) or new programs (for language [6.11] or library features [7.26]) is discouraged.

3This International Standard is divided into four major subdivisions:— preliminary elements (clauses 1−4);— the characteristics of environments that translate and execute C programs (clause 5);— the language syntax, constraints, and semantics (clause 6);— the library facilities (clause 7).

4

Examples are provided to illustrate possible forms of the constructions described.
Footnotes are provided to emphasize consequences of the rules described in that
subclause or elsewhere in this International Standard. References are used to refer toother related subclauses. Recommendations are provided to give advice or guidance toimplementors. Annexes provide additional information and summarize the information
contained in this International Standard. A bibliography lists documents that werereferred to during the preparation of the standard.

5

The language clause (clause 6) is derived from ‘‘The C Reference Manual’’.

6

The library clause (clause 7) is based on the 1984 /usr/group Standard.

xiv

Introduction

INTERNATIONAL STANDARD©ISO/IEC

ISO/IEC 9899:TC3

Programming languages — C

1. Scope
1

This International Standard specifies the form and establishes the interpretation ofprograms written in the C programming language.1) It specifies— the representation of C programs;— the syntax and constraints of the C language;— the semantic rules for interpreting C programs;— the representation of input data to be processed by C programs;— the representation of output data produced by C programs;— the restrictions and limits imposed by a conforming implementation of C.

2This International Standard does not specify— the mechanism by which C programs are transformed for use by a data-processing
system;— the mechanism by which C programs are invoked for use by a data-processing
system;— the mechanism by which input data are transformed for use by a C program;— the mechanism by which output data are transformed after being produced by a C
program;— the size or complexity of a program and its data that will exceed the capacity of any
specific data-processing system or the capacity of a particular processor;

1)§1This International Standard is designed to promote the portability of C programs among a variety ofdata-processing systems. It is intended for use by implementors and programmers.

General1ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

WG14/N1256— all minimal requirements of a data-processing system that is capable of supporting a
conforming implementation.

2. Normative references
1

The following normative documents contain provisions which, through reference in thistext, constitute provisions of this International Standard. For dated references,subsequent amendments to, or revisions of, any of these publications do not apply.
However, parties to agreements based on this International Standard are encouraged toinvestigate the possibility of applying the most recent editions of the normative
documents indicated below. For undated references, the latest edition of the normative
document referred to applies. Members of ISO and IEC maintain registers of currently
valid International Standards.

2

ISO 31−11:1992, Quantities and units — Part 11: Mathematical signs and symbols foruse in the physical sciences and technology.

3

ISO/IEC 646, Information technology — ISO 7-bit coded character set for informationinterchange.

4

ISO/IEC 2382−1:1993, Information technology — Vocabulary — Part 1: Fundamental
terms.

5

ISO 4217, Codes for the representation of currencies and funds.

6

ISO 8601, Data elements and interchange formats — Information interchange —Representation of dates and times.

7

ISO/IEC 10646 (all parts), Information technology — Universal Multiple-Octet Coded
Character Set (UCS).

8

IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
designated IEC 559:1989).

2

General§2

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

3. Terms, definitions, and symbols
1

For the purposes of this International Standard, the following definitions apply. Other
terms are defined where they appear in italic type or on the left side of a syntax rule.
Terms explicitly defined in this International Standard are not to be presumed to refer
implicitly to similar terms defined elsewhere. Terms not defined in this International
Standard are to be interpreted according to ISO/IEC 2382−1. Mathematical symbols notdefined in this International Standard are to be interpreted according to ISO 31−11.

3.1
1access〈execution-time action〉 to read or modify the value of an object

2

NOTE 1

Where only one of these two actions is meant, ‘‘read’’ or ‘‘modify’’ is used.

3
4

NOTE 2"Modify’’ includes the case where the new value being stored is the same as the previous value.

NOTE 3

Expressions that are not evaluated do not access objects.

3.2
1alignment
requirement that objects of a particular type be located on storage boundaries withaddresses that are particular multiples of a byte address

3.3
1

argument
actual argument
actual parameter (deprecated)
expression in the comma-separated list bounded by the parentheses in a function call
expression, or a sequence of preprocessing tokens in the comma-separated list boundedby the parentheses in a function-like macro invocation

3.4
1

behavior
external appearance or action

3.4.1
1

implementation-defined behavior
unspecified behavior where each implementation documents how the choice is made2

EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
when a signed integer is shifted right.

3.4.2
1

locale-specific behavior
behavior that depends on local conventions of nationality, culture, and language that each
implementation documents§3.4.2

General3ISO/IEC 9899:TC3

2

Committee Draft — Septermber 7, 2007

WG14/N1256

EXAMPLE An example of locale-specific behavior is whether the islower function returns true forcharacters other than the 26 lowercase Latin letters.

3.4.3
1

undefined behavior
behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
for which this International Standard imposes no requirements

2

NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
results, to behaving during translation or program execution in a documented manner characteristic of theenvironment (with or without the issuance of a diagnostic message), to terminating a translation or
execution (with the issuance of a diagnostic message).

3

EXAMPLEAn example of undefined behavior is the behavior on integer overflow.

3.4.4
1

unspecified behavior
use of an unspecified value, or other behavior where this International Standard provides
two or more possibilities and imposes no further requirements on which is chosen in any
instance2

EXAMPLEevaluated.

An example of unspecified behavior is the order in which the arguments to a function are

3.5
1

bit
unit of data storage in the execution environment large enough to hold an object that may
have one of two values

2

NOTE

It need not be possible to express the address of each individual bit of an object.

3.6
1

byte
addressable unit of data storage large enough to hold any member of the basic characterset of the execution environment

2
3

NOTE 1

It is possible to express the address of each individual byte of an object uniquely.

NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementationdefined. The least significant bit is called the low-order bit; the most significant bit is called the high-order
bit.

3.7
1

character〈abstract〉 member of a set of elements used for the organization, control, or
representation of data

3.7.1
1

charactersingle-byte character〈C〉 bit representation that fits in a byte
4

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3.7.2
1

multibyte character
sequence of one or more bytes representing a member of the extended character set ofeither the source or the execution environment

2

NOTE

The extended character set is a superset of the basic character set.

3.7.3
1

wide character
bit representation that fits in an object of type wchar_t, capable of representing any
character in the current locale

3.8
1

constraint
restriction, either syntactic or semantic, by which the exposition of language elements is
to be interpreted

3.9
1

correctly rounded result
representation in the result format that is nearest in value, subject to the current rounding
mode, to what the result would be given unlimited range and precision

3.10
1

diagnostic message
message belonging to an implementation-defined subset of the implementation’s message
output3.11
1

forward reference
reference to a later subclause of this International Standard that contains additional
information relevant to this subclause

3.12
1

implementation
particular set of software, running in a particular translation environment under particular
control options, that performs translation of programs for, and supports execution offunctions in, a particular execution environment

3.13
1

implementation limit
restriction imposed upon programs by the implementation

3.14
1

objectregion of data storage in the execution environment, the contents of which can represent
values§3.14

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2

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When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.

3.15
1

parameter
formal parameter
formal argument (deprecated)
object declared as part of a function declaration or definition that acquires a value on
entry to the function, or an identifier from the comma-separated list bounded by theparentheses immediately following the macro name in a function-like macro definition

3.16
1

recommended practicespecification that is strongly recommended as being in keeping with the intent of thestandard, but that may be impractical for some implementations

3.17
1

value
precise meaning of the contents of an object when interpreted as having a specific type3.17.1
1

implementation-defined value
unspecified value where each implementation documents how the choice is made3.17.2
1

indeterminate value
either an unspecified value or a trap representation

3.17.31

unspecified value
valid value of the relevant type where this International Standard imposes norequirements on which value is chosen in any instance

2

NOTE

An unspecified value cannot be a trap representation.

3.18
1

 x
ceiling of x: the least integer greater than or equal to x

2

EXAMPLE2. 4 is 3, −2. 4 is −2.

3.19
1

 x
floor of x: the greatest integer less than or equal to x

2

EXAMPLE6

2. 4 is 2, −2. 4 is −3.

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4. Conformance1

In this International Standard, ‘‘shall’’ is to be interpreted as a requirement on an
implementation or on a program; conversely, ‘‘shall not’’ is to be interpreted as aprohibition.

2

If a ‘‘shall’’ or ‘‘shall not’’ requirement that appears outside of a constraint is violated, thebehavior is undefined. Undefined behavior is otherwise indicated in this International
Standard by the words ‘‘undefined behavior’’ or by the omission of any explicit definitionof behavior. There is no difference in emphasis among these three; they all describe‘‘behavior that is undefined’’.

3

A program that is correct in all other aspects, operating on correct data, containing
unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.

4

The implementation shall not successfully translate a preprocessing translation unit
containing a #error preprocessing directive unless it is part of a group skipped byconditional inclusion.

5

A strictly conforming program shall use only those features of the language and libraryspecified in this International Standard.2) It shall not produce output dependent on any
unspecified, undefined, or implementation-defined behavior, and shall not exceed any
minimum implementation limit.

6

The two forms of conforming implementation are hosted and freestanding. A conforming
hosted implementation shall accept any strictly conforming program. A conforming
freestanding implementation shall accept any strictly conforming program that does notuse complex types and in which the use of the features specified in the library clause(clause 7) is confined to the contents of the standard headers <float.h>,<iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>, <stddef.h>, and<stdint.h>. A conforming implementation may have extensions (including additional
library functions), provided they do not alter the behavior of any strictly conforming
program.3)

2)

A strictly conforming program can use conditional features (such as those in annex F) provided theuse is guarded by a #ifdef directive with the appropriate macro. For example:#ifdef _ _STDC_IEC_559_ _ /* FE_UPWARD defined *//* ... */fesetround(FE_UPWARD);/* ... */#endif3)§4This implies that a conforming implementation reserves no identifiers other than those explicitly
reserved in this International Standard.

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7

A conforming program is one that is acceptable to a conforming implementation.4)

8

An implementation shall be accompanied by a document that defines all implementationdefined and locale-specific characteristics and all extensions.
Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>(7.9), sizes of integer types <limits.h> (7.10), variable arguments <stdarg.h>(7.15), boolean type and values <stdbool.h> (7.16), common definitions<stddef.h> (7.17), integer types <stdint.h> (7.18).

4)8Strictly conforming programs are intended to be maximally portable among conforming
implementations. Conforming programs may depend upon nonportable features of a conforming
implementation.

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5. Environment1

An implementation translates C source files and executes C programs in two dataprocessing-system environments, which will be called the translation environment andthe execution environment in this International Standard. Their characteristics define andconstrain the results of executing conforming C programs constructed according to thesyntactic and semantic rules for conforming implementations.
Forward references: In this clause, only a few of many possible forward references
have been noted.

5.1 Conceptual models
5.1.1 Translation environment
5.1.1.1 Program structure
1

A C program need not all be translated at the same time. The text of the program is kept
in units called source files, (or preprocessing files) in this International Standard. A
source file together with all the headers and source files included via the preprocessing
directive #include is known as a preprocessing translation unit. After preprocessing, apreprocessing translation unit is called a translation unit. Previously translated translation
units may be preserved individually or in libraries. The separate translation units of aprogram communicate by (for example) calls to functions whose identifiers have external
linkage, manipulation of objects whose identifiers have external linkage, or manipulationof data files. Translation units may be separately translated and then later linked to
produce an executable program.
Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
preprocessing directives (6.10).

5.1.1.2 Translation phases
1

The precedence among the syntax rules of translation is specified by the following
phases.5)
1.

5)

Physical source file multibyte characters are mapped, in an implementationdefined manner, to the source character set (introducing new-line characters for
end-of-line indicators) if necessary. Trigraph sequences are replaced bycorresponding single-character internal representations.

Implementations shall behave as if these separate phases occur, even though many are typically folded
together in practice. Source files, translation units, and translated translation units need notnecessarily be stored as files, nor need there be any one-to-one correspondence between these entities
and any external representation. The description is conceptual only, and does not specify any
particular implementation.

§5.1.1.2

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2.

Each instance of a backslash character (\) immediately followed by a new-line
character is deleted, splicing physical source lines to form logical source lines.
Only the last backslash on any physical source line shall be eligible for being partof such a splice. A source file that is not empty shall end in a new-line character,which shall not be immediately preceded by a backslash character before any suchsplicing takes place.

3.

The source file is decomposed into preprocessing tokens6) and sequences ofwhite-space characters (including comments). A source file shall not end in apartial preprocessing token or in a partial comment. Each comment is replaced by
one space character. New-line characters are retained. Whether each nonempty
sequence of white-space characters other than new-line is retained or replaced by
one space character is implementation-defined.

4.

Preprocessing directives are executed, macro invocations are expanded, and_Pragma unary operator expressions are executed. If a character sequence thatmatches the syntax of a universal character name is produced by token
concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
directive causes the named header or source file to be processed from phase 1
through phase 4, recursively. All preprocessing directives are then deleted.

5.

Each source character set member and escape sequence in character constants andstring literals is converted to the corresponding member of the execution character
set; if there is no corresponding member, it is converted to an implementationdefined member other than the null (wide) character.7)

6.

Adjacent string literal tokens are concatenated.

7.

White-space characters separating tokens are no longer significant. Each
preprocessing token is converted into a token. The resulting tokens aresyntactically and semantically analyzed and translated as a translation unit.

8.

All external object and function references are resolved. Library components arelinked to satisfy external references to functions and objects not defined in thecurrent translation. All such translator output is collected into a program image
which contains information needed for execution in its execution environment.

Forward references: universal character names (6.4.3), lexical elements (6.4),
preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).

6)

As described in 6.4, the process of dividing a source file’s characters into preprocessing tokens iscontext-dependent. For example, see the handling of < within a #include preprocessing directive.

7)

An implementation need not convert all non-corresponding source characters to the same execution
character.

10Environment§5.1.1.2

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5.1.1.3 Diagnostics
1

A conforming implementation shall produce at least one diagnostic message (identified in
an implementation-defined manner) if a preprocessing translation unit or translation unit
contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
specified as undefined or implementation-defined. Diagnostic messages need not be
produced in other circumstances.8)2

EXAMPLEAn implementation shall issue a diagnostic for the translation unit:

char i;
int i;
because in those cases where wording in this International Standard describes the behavior for a construct
as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.

5.1.2 Execution environments
1

Two execution environments are defined: freestanding and hosted. In both cases,
program startup occurs when a designated C function is called by the execution
environment. All objects with static storage duration shall be initialized (set to theirinitial values) before program startup. The manner and timing of such initialization areotherwise unspecified. Program termination returns control to the execution
environment.
Forward references: storage durations of objects (6.2.4), initialization (6.7.8).

5.1.2.1 Freestanding environment
1

In a freestanding environment (in which C program execution may take place without any
benefit of an operating system), the name and type of the function called at program
startup are implementation-defined. Any library facilities available to a freestanding
program, other than the minimal set required by clause 4, are implementation-defined.

2

The effect of program termination in a freestanding environment is implementationdefined.

5.1.2.2 Hosted environment
1

A hosted environment need not be provided, but shall conform to the following
specifications if present.

8)

The intent is that an implementation should identify the nature of, and where possible localize, eachviolation. Of course, an implementation is free to produce any number of diagnostics as long as avalid program is still correctly translated. It may also successfully translate an invalid program.

§5.1.2.2

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5.1.2.2.1 Program startup
1

The function called at program startup is named main. The implementation declares no
prototype for this function. It shall be defined with a return type of int and with noparameters:
int main(void) { /* ... */ }or with two parameters (referred to here as argc and argv, though any names may be
used, as they are local to the function in which they are declared):
int main(int argc, char *argv[]) { /* ... */ }or equivalent;9) or in some other implementation-defined manner.

2

If they are declared, the parameters to the main function shall obey the following
constraints:— The value of argc shall be nonnegative.
— argv[argc] shall be a null pointer.
— If the value of argc is greater than zero, the array members argv[0] throughargv[argc-1] inclusive shall contain pointers to strings, which are given
implementation-defined values by the host environment prior to program startup. The
intent is to supply to the program information determined prior to program startup
from elsewhere in the hosted environment. If the host environment is not capable ofsupplying strings with letters in both uppercase and lowercase, the implementation
shall ensure that the strings are received in lowercase.
— If the value of argc is greater than zero, the string pointed to by argv[0]represents the program name; argv[0][0] shall be the null character if the
program name is not available from the host environment. If the value of argc is
greater than one, the strings pointed to by argv[1] through argv[argc-1]
represent the program parameters.
— The parameters argc and argv and the strings pointed to by the argv array shallbe modifiable by the program, and retain their last-stored values between program
startup and program termination.

5.1.2.2.2 Program execution
1

In a hosted environment, a program may use all the functions, macros, type definitions,and objects described in the library clause (clause 7).

9)12Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
char ** argv, and so on.

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5.1.2.2.3 Program termination
1

If the return type of the main function is a type compatible with int, a return from theinitial call to the main function is equivalent to calling the exit function with the value
returned by the main function as its argument;10) reaching the } that terminates themain function returns a value of 0. If the return type is not compatible with int, thetermination status returned to the host environment is unspecified.
Forward references: definition of terms (7.1.1), the exit function (7.20.4.3).

5.1.2.3 Program execution
1

The semantic descriptions in this International Standard describe the behavior of an
abstract machine in which issues of optimization are irrelevant.

2

Accessing a volatile object, modifying an object, modifying a file, or calling a functionthat does any of those operations are all side effects,11) which are changes in the state of
the execution environment. Evaluation of an expression may produce side effects. At
certain specified points in the execution sequence called sequence points, all side effects
of previous evaluations shall be complete and no side effects of subsequent evaluations
shall have taken place. (A summary of the sequence points is given in annex C.)

3

In the abstract machine, all expressions are evaluated as specified by the semantics. An
actual implementation need not evaluate part of an expression if it can deduce that its
value is not used and that no needed side effects are produced (including any caused bycalling a function or accessing a volatile object).

4

When the processing of the abstract machine is interrupted by receipt of a signal, only thevalues of objects as of the previous sequence point may be relied on. Objects that may be
modified between the previous sequence point and the next sequence point need not havereceived their correct values yet.

5

The least requirements on a conforming implementation are:
— At sequence points, volatile objects are stable in the sense that previous accesses arecomplete and subsequent accesses have not yet occurred.

10) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
will have ended in the former case, even where they would not have in the latter.
11) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
values of floating-point operations. Implementations that support such floating-point state are
required to regard changes to it as side effects — see annex F for details. The floating-point
environment library <fenv.h> provides a programming facility for indicating when these side
effects matter, freeing the implementations in other cases.

§5.1.2.3

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WG14/N1256— At program termination, all data written into files shall be identical to the result that
execution of the program according to the abstract semantics would have produced.
— The input and output dynamics of interactive devices shall take place as specified in
7.19.3. The intent of these requirements is that unbuffered or line-buffered output
appear as soon as possible, to ensure that prompting messages actually appear prior toa program waiting for input.
6

What constitutes an interactive device is implementation-defined.

7

More stringent correspondences between abstract and actual semantics may be defined byeach implementation.

8

EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
semantics: at every sequence point, the values of the actual objects would agree with those specified by theabstract semantics. The keyword volatile would then be redundant.

9

Alternatively, an implementation might perform various optimizations within each translation unit, suchthat the actual semantics would agree with the abstract semantics only when making function calls acrosstranslation unit boundaries. In such an implementation, at the time of each function entry and function
return where the calling function and the called function are in different translation units, the values of all
externally linked objects and of all objects accessible via pointers therein would agree with the abstract
semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
function and of all objects accessible via pointers therein would agree with the abstract semantics. In thistype of implementation, objects referred to by interrupt service routines activated by the signal function
would require explicit specification of volatile storage, as well as other implementation-defined
restrictions.

10

EXAMPLE 2

In executing the fragment

char c1, c2;/* ... */c1 = c1 + c2;
the ‘‘integer promotions’’ require that the abstract machine promote the value of each variable to int size
and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
produce the same result, possibly omitting the promotions.

11

EXAMPLE 3

Similarly, in the fragment

float f1, f2;
double d;/* ... */f1 = f2 * d;the multiplication may be executed using single-precision arithmetic if the implementation can ascertainthat the result would be the same as if it were executed using double-precision arithmetic (for example, if dwere replaced by the constant 2.0, which has type double).

14

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EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
semantics. Values are independent of whether they are represented in a register or in memory. For
example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
is required to round to the precision of the storage type. In particular, casts and assignments are required toperform their specified conversion. For the fragment
double d1, d2;
float f;d1 = f = expression;
d2 = (float) expression;

the values assigned to d1 and d2 are required to have been converted to float.

13

EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations inprecision as well as range. The implementation cannot generally apply the mathematical associative rules
for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence ofoverflow and underflow. Likewise, implementations cannot generally replace decimal constants in order torearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
numbers are often not valid (see F.8).
double x, y, z;/* ... */x = (x * y) * z; // not equivalent to x *= y * z;z = (x - y) + y ; // not equivalent to z = x;z = x + x * y;// not equivalent to z = x * (1.0 + y);y = x / 5.0;// not equivalent to y = x * 0.2;

14EXAMPLE 6

To illustrate the grouping behavior of expressions, in the following fragment

int a, b;/* ... */a = a + 32760 + b + 5;
the expression statement behaves exactly the same asa = (((a + 32760) + b) + 5);
due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine inwhich overflows produce an explicit trap and in which the range of values representable by an int is[−32768, +32767], the implementation cannot rewrite this expression asa = ((a + b) + 32765);
since if the values for a and b were, respectively, −32754 and −15, the sum a + b would produce a trap
while the original expression would not; nor can the expression be rewritten either as
a = ((a + 32765) + b);ora = (a + (b + 32765));
since the values for a and b might have been, respectively, 4 and −8 or −17 and 12. However, on a machine
in which overflow silently generates some value and where positive and negative overflows cancel, theabove expression statement can be rewritten by the implementation in any of the above ways because thesame result will occur.

§5.1.2.3

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EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In thefollowing fragment#include <stdio.h>
int sum;char *p;/* ... */sum = sum * 10 - '0' + (*p++ = getchar());
the expression statement is grouped as if it were written as
sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
but the actual increment of p can occur at any time between the previous sequence point and the next
sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned
value.

Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), thesignal function (7.14), files (7.19.3).

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5.2 Environmental considerations
5.2.1 Character sets
1

Two sets of characters and their associated collating sequences shall be defined: the set inwhich source files are written (the source character set), and the set interpreted in theexecution environment (the execution character set). Each set is further divided into abasic character set, whose contents are given by this subclause, and a set of zero or more
locale-specific members (which are not members of the basic character set) called
extended characters. The combined set is also called the extended character set. The
values of the members of the execution character set are implementation-defined.

2

In a character constant or string literal, members of the execution character set shall be
represented by corresponding members of the source character set or by escapesequences consisting of the backslash \ followed by one or more characters. A byte withall bits set to 0, called the null character, shall exist in the basic execution character set; it
is used to terminate a character string.

3

Both the basic source and basic execution character sets shall have the following
members: the 26 uppercase letters of the Latin alphabet
A
N

B
O

C
P

D
Q

E
R

F
S

G
T

H
U

I
V

J
W

K
X

L
Y

M
Z

k
x

l
y

m
z

,
{

|

.
}

the 26 lowercase letters of the Latin alphabet
a
n

b
o

c
p

d
q

e
r

f
s

g
t

h
u

i
v

j
w

3

4

5

6

7

8

9

)
]

*
^

+
_

the 10 decimal digits
0

1

2

the following 29 graphic characters
!
;

"
<

#
=

%
>

&
?

'
[

(
\

/
~

:

the space character, and control characters representing horizontal tab, vertical tab, andform feed. The representation of each member of the source and execution basic
character sets shall fit in a byte. In both the source and execution basic character sets, thevalue of each character after 0 in the above list of decimal digits shall be one greater thanthe value of the previous. In source files, there shall be some way of indicating the end ofeach line of text; this International Standard treats such an end-of-line indicator as if itwere a single new-line character. In the basic execution character set, there shall becontrol characters representing alert, backspace, carriage return, and new line. If any
other characters are encountered in a source file (except in an identifier, a character
constant, a string literal, a header name, a comment, or a preprocessing token that is never§5.2.1

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converted to a token), the behavior is undefined.
4

A letter is an uppercase letter or a lowercase letter as defined above; in this International
Standard the term does not include other characters that are letters in other alphabets.

5

The universal character name construct provides a way to name other characters.
Forward references: universal character names (6.4.3), character constants (6.4.4.4),
preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).

5.2.1.1 Trigraph sequences
1

Before any other processing takes place, each occurrence of one of the following
sequences of three characters (called trigraph sequences12)) is replaced with thecorresponding single character.

??=
??(
??/

#
[
\

??)
??'
??<

]
^
{

??!
??>
??-

|
}
~

No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
above is not changed.

2

EXAMPLE 1??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)

becomes#define arraycheck(a, b) a[b] || b[a]3EXAMPLE 2

The following source line

printf("Eh???/n");becomes (after replacement of the trigraph sequence ??/)
printf("Eh?\n");5.2.1.2 Multibyte characters
1

The source character set may contain multibyte characters, used to represent members of
the extended character set. The execution character set may also contain multibyte
characters, which need not have the same encoding as for the source character set. For
both character sets, the following shall hold:— The basic character set shall be present and each character shall be encoded as asingle byte.
— The presence, meaning, and representation of any additional members is localespecific.
12) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.

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ISO/IEC 9899:TC3— A multibyte character set may have a state-dependent encoding, wherein eachsequence of multibyte characters begins in an initial shift state and enters otherlocale-specific shift states when specific multibyte characters are encountered in thesequence. While in the initial shift state, all single-byte characters retain their usualinterpretation and do not alter the shift state. The interpretation for subsequent bytes
in the sequence is a function of the current shift state.
— A byte with all bits zero shall be interpreted as a null character independent of shiftstate. Such a byte shall not occur as part of any other multibyte character.

2

For source files, the following shall hold:— An identifier, comment, string literal, character constant, or header name shall begin
and end in the initial shift state.
— An identifier, comment, string literal, character constant, or header name shall consistof a sequence of valid multibyte characters.

5.2.2 Character display semantics
1

The active position is that location on a display device where the next character output by
the fputc function would appear. The intent of writing a printing character (as definedby the isprint function) to a display device is to display a graphic representation ofthat character at the active position and then advance the active position to the next
position on the current line. The direction of writing is locale-specific. If the active
position is at the final position of a line (if there is one), the behavior of the display device
is unspecified.

2

Alphabetic escape sequences representing nongraphic characters in the execution
character set are intended to produce actions on display devices as follows:\a (alert) Produces an audible or visible alert without changing the active position.
\b (backspace) Moves the active position to the previous position on the current line. If
the active position is at the initial position of a line, the behavior of the display
device is unspecified.
\f ( form feed) Moves the active position to the initial position at the start of the next
logical page.
\n (new line) Moves the active position to the initial position of the next line.
\r (carriage return) Moves the active position to the initial position of the current line.
\t (horizontal tab) Moves the active position to the next horizontal tabulation positionon the current line. If the active position is at or past the last defined horizontal
tabulation position, the behavior of the display device is unspecified.
\v (vertical tab) Moves the active position to the initial position of the next verticaltabulation position. If the active position is at or past the last defined vertical§5.2.2
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tabulation position, the behavior of the display device is unspecified.
3

Each of these escape sequences shall produce a unique implementation-defined value
which can be stored in a single char object. The external representations in a text fileneed not be identical to the internal representations, and are outside the scope of thisInternational Standard.
Forward references: the isprint function (7.4.1.8), the fputc function (7.19.7.3).

5.2.3 Signals and interrupts
1

Functions shall be implemented such that they may be interrupted at any time by a signal,
or may be called by a signal handler, or both, with no alteration to earlier, but still active,
invocations’ control flow (after the interruption), function return values, or objects with
automatic storage duration. All such objects shall be maintained outside the function
image (the instructions that compose the executable representation of a function) on a
per-invocation basis.

5.2.4 Environmental limits
1

Both the translation and execution environments constrain the implementation of
language translators and libraries. The following summarizes the language-related
environmental limits on a conforming implementation; the library-related limits are
discussed in clause 7.

5.2.4.1 Translation limits
1

The implementation shall be able to translate and execute at least one program that
contains at least one instance of every one of the following limits:13)— 127 nesting levels of blocks— 63 nesting levels of conditional inclusion— 12 pointer, array, and function declarators (in any combinations) modifying anarithmetic, structure, union, or incomplete type in a declaration— 63 nesting levels of parenthesized declarators within a full declarator— 63 nesting levels of parenthesized expressions within a full expression— 63 significant initial characters in an internal identifier or a macro name (eachuniversal character name or extended source character is considered a single
character)— 31 significant initial characters in an external identifier (each universal character namespecifying a short identifier of 0000FFFF or less is considered 6 characters, each13) Implementations should avoid imposing fixed translation limits whenever possible.

20

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universal character name specifying a short identifier of 00010000 or more isconsidered 10 characters, and each extended source character is considered the same
number of characters as the corresponding universal character name, if any)14)— 4095 external identifiers in one translation unit
— 511 identifiers with block scope declared in one block— 4095 macro identifiers simultaneously defined in one preprocessing translation unit
— 127 parameters in one function definition— 127 arguments in one function call
— 127 parameters in one macro definition— 127 arguments in one macro invocation— 4095 characters in a logical source line
— 4095 characters in a character string literal or wide string literal (after concatenation)— 65535 bytes in an object (in a hosted environment only)— 15 nesting levels for #included files— 1023 case labels for a switch statement (excluding those for any nested switch
statements)— 1023 members in a single structure or union— 1023 enumeration constants in a single enumeration— 63 levels of nested structure or union definitions in a single struct-declaration-list

5.2.4.2 Numerical limits
1

An implementation is required to document all the limits specified in this subclause,
which are specified in the headers <limits.h> and <float.h>. Additional limits are
specified in <stdint.h>.
Forward references: integer types <stdint.h> (7.18).

5.2.4.2.1 Sizes of integer types <limits.h>
1

The values given below shall be replaced by constant expressions suitable for use in #if
preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, thefollowing shall be replaced by expressions that have the same type as would anexpression that is an object of the corresponding type converted according to the integer
promotions. Their implementation-defined values shall be equal or greater in magnitude

14) See ‘‘future language directions’’ (6.11.3).

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— number of bits for smallest object that is not a bit-field (byte)
CHAR_BIT
8— minimum value for an object of type signed char
SCHAR_MIN-127 // −(27 − 1)
— maximum value for an object of type signed char
SCHAR_MAX+127 // 27 − 1— maximum value for an object of type unsigned char
UCHAR_MAX
255 // 28 − 1— minimum value for an object of type char
CHAR_MIN
see below— maximum value for an object of type char
CHAR_MAXsee below— maximum number of bytes in a multibyte character, for any supported locale
MB_LEN_MAX
1— minimum value for an object of type short int
SHRT_MIN-32767 // −(215 − 1)
— maximum value for an object of type short int
SHRT_MAX+32767 // 215 − 1— maximum value for an object of type unsigned short int
USHRT_MAX
65535 // 216 − 1— minimum value for an object of type int
INT_MIN-32767 // −(215 − 1)
— maximum value for an object of type int
INT_MAX+32767 // 215 − 1— maximum value for an object of type unsigned int
UINT_MAX
65535 // 216 − 1— minimum value for an object of type long int
LONG_MIN-2147483647 // −(231 − 1)
— maximum value for an object of type long int
LONG_MAX+2147483647 // 231 − 1— maximum value for an object of type unsigned long int
ULONG_MAX
4294967295 // 232 − 1

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ISO/IEC 9899:TC3— minimum value for an object of type long long int
LLONG_MIN-9223372036854775807 // −(263 − 1)
— maximum value for an object of type long long int
LLONG_MAX+9223372036854775807 // 263 − 1— maximum value for an object of type unsigned long long int
ULLONG_MAX
18446744073709551615 // 264 − 1
2

If the value of an object of type char is treated as a signed integer when used in an
expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and thevalue of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
UCHAR_MAX.15) The value UCHAR_MAX shall equal 2CHAR_BIT − 1.
Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).

5.2.4.2.2 Characteristics of floating types <float.h>1

The characteristics of floating types are defined in terms of a model that describes a
representation of floating-point numbers and values that provide information about animplementation’s floating-point arithmetic.16) The following parameters are used todefine the model for each floating-point type:
s
b
e
p
fk

2

sign (±1)
base or radix of exponent representation (an integer > 1)
exponent (an integer between a minimum emin and a maximum emax )precision (the number of base-b digits in the significand)nonnegative integers less than b (the significand digits)

A floating-point number (x) is defined by the following model:px = sb e Σ f k b−k ,emin ≤ e ≤ emax

k=1

3

In addition to normalized floating-point numbers ( f 1 > 0 if x ≠ 0), floating types may beable to contain other kinds of floating-point numbers, such as subnormal floating-point
numbers (x ≠ 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x ≠ 0,e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
through almost every arithmetic operation without raising a floating-point exception; asignaling NaN generally raises a floating-point exception when occurring as an15) See 6.2.5.
16) The floating-point model is intended to clarify the description of each floating-point characteristic anddoes not require the floating-point arithmetic of the implementation to be identical.

§5.2.4.2.2

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arithmetic operand.17)
4

An implementation may give zero and non-numeric values (such as infinities and NaNs) asign or may leave them unsigned. Wherever such values are unsigned, any requirementin this International Standard to retrieve the sign shall produce an unspecified sign, andany requirement to set the sign shall be ignored.

5

The accuracy of the floating-point operations (+, -, *, /) and of the library functions in<math.h> and <complex.h> that return floating-point results is implementationdefined, as is the accuracy of the conversion between floating-point internal
representations and string representations performed by the library functions in<stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that theaccuracy is unknown.

6

All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant
expressions suitable for use in #if preprocessing directives; all floating values shall be
constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX,
and FLT_ROUNDS have separate names for all three floating-point types. The floatingpoint model representation is provided for all values except FLT_EVAL_METHOD and
FLT_ROUNDS.

7

The rounding mode for floating-point addition is characterized by the implementationdefined value of FLT_ROUNDS:18)
-1
0
1
2
3

indeterminable
toward zeroto nearest
toward positive infinity
toward negative infinity

All other values for FLT_ROUNDS characterize implementation-defined rounding
behavior.
8

Except for assignment and cast (which remove all extra range and precision), the valuesof operations with floating operands and values subject to the usual arithmetic
conversions and of floating constants are evaluated to a format whose range and precision
may be greater than required by the type. The use of evaluation formats is characterized
by the implementation-defined value of FLT_EVAL_METHOD:19)

17) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings withsimilar behavior.
18) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode throughthe function fesetround in <fenv.h>.

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indeterminable;

0evaluate all operations and constants just to the range and precision of the
type;

1

evaluate operations and constants of type float and double to therange and precision of the double type, evaluate long double
operations and constants to the range and precision of the long double
type;

2

evaluate all operations and constants to the range and precision of thelong double type.

All other negative values for FLT_EVAL_METHOD characterize implementation-defined
behavior.
9

The values given in the following list shall be replaced by constant expressions with
implementation-defined values that are greater or equal in magnitude (absolute value) tothose shown, with the same sign:— radix of exponent representation, b
FLT_RADIX

2— number of base-FLT_RADIX digits in the floating-point significand, p
FLT_MANT_DIG
DBL_MANT_DIG
LDBL_MANT_DIG— number of decimal digits, n, such that any floating-point number in the widest
supported floating type with pmax radix b digits can be rounded to a floating-point
number with n decimal digits and back again without change to the value, pmax log10 b
if b is a power of 10 1 + pmax log10 b otherwise
DECIMAL_DIG

10— number of decimal digits, q, such that any floating-point number with q decimal digits
can be rounded into a floating-point number with p radix b digits and back again
without change to the q decimal digits,19) The evaluation method determines evaluation formats of expressions involving all floating types, notjust real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float_Complex operands is represented in the double _Complex format, and its parts are evaluated to
double.

§5.2.4.2.2

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 p log10 b
if b is a power of 10 ( p − 1) log10 b otherwise
FLT_DIG6
DBL_DIG10
LDBL_DIG
10— minimum negative integer such that FLT_RADIX raised to one less than that power isa normalized floating-point number, emin
FLT_MIN_EXP
DBL_MIN_EXP
LDBL_MIN_EXP— minimum negative integer such that 10 raised to that power is in the range of
normalized floating-point numbers, log10 b emin −1 
FLT_MIN_10_EXP-37
DBL_MIN_10_EXP-37
LDBL_MIN_10_EXP-37— maximum integer such that FLT_RADIX raised to one less than that power is a
representable finite floating-point number, emax
FLT_MAX_EXP
DBL_MAX_EXP
LDBL_MAX_EXP— maximum integer such that 10 raised to that power is in the range of representable
finite floating-point numbers, log10 ((1 − b− p )b emax )
FLT_MAX_10_EXP
DBL_MAX_10_EXP
LDBL_MAX_10_EXP
10

+37
+37
+37

The values given in the following list shall be replaced by constant expressions with
implementation-defined values that are greater than or equal to those shown:— maximum representable finite floating-point number, (1 − b− p )b emax
FLT_MAX
DBL_MAXLDBL_MAX

11

1E+37
1E+37
1E+37

The values given in the following list shall be replaced by constant expressions with
implementation-defined (positive) values that are less than or equal to those shown:— the difference between 1 and the least value greater than 1 that is representable in thegiven floating point type, b1− p
26
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FLT_EPSILON
DBL_EPSILON
LDBL_EPSILON

ISO/IEC 9899:TC3

1E-5
1E-9
1E-9

— minimum normalized positive floating-point number, b emin −1
FLT_MIN
DBL_MIN
LDBL_MIN

1E-37
1E-37
1E-37

Recommended practice12

Conversion from (at least) double to decimal with DECIMAL_DIG digits and backshould be the identity function.

13

EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
requirements of this International Standard, and the appropriate values in a <float.h> header for typefloat:
6

x = s16e Σ f k 16−k , −31 ≤ e ≤ +32
k=1

FLT_RADIX
FLT_MANT_DIG
FLT_EPSILON
FLT_DIG
FLT_MIN_EXP
FLT_MIN
FLT_MIN_10_EXP
FLT_MAX_EXP
FLT_MAXFLT_MAX_10_EXP

14

16
6
9.53674316E-07F
6-31
2.93873588E-39F-38+32
3.40282347E+38F+38

EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
single-precision and double-precision normalized numbers in IEC 60559,20) and the appropriate values in a
<float.h> header for types float and double:
24

x f = s2e Σ f k 2−k , −125 ≤ e ≤ +128k=1
53

x d = s2e Σ f k 2−k , −1021 ≤ e ≤ +1024
k=1

FLT_RADIX
DECIMAL_DIG
FLT_MANT_DIG
FLT_EPSILON
FLT_EPSILON

2
17
24
1.19209290E-07F // decimal constant
0X1P-23F // hex constant20) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
limits are one less than shown here.

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FLT_DIG
6
FLT_MIN_EXP-125
FLT_MIN
1.17549435E-38F // decimal constant
FLT_MIN
0X1P-126F // hex constant
FLT_MIN_10_EXP-37
FLT_MAX_EXP+128
FLT_MAX
3.40282347E+38F // decimal constant
FLT_MAX
0X1.fffffeP127F // hex constant
FLT_MAX_10_EXP+38
DBL_MANT_DIG
53
DBL_EPSILON 2.2204460492503131E-16 // decimal constant
DBL_EPSILON
0X1P-52 // hex constant
DBL_DIG15
DBL_MIN_EXP-1021
DBL_MIN
2.2250738585072014E-308 // decimal constant
DBL_MIN
0X1P-1022 // hex constant
DBL_MIN_10_EXP-307
DBL_MAX_EXP+1024
DBL_MAX
1.7976931348623157E+308 // decimal constant
DBL_MAX
0X1.fffffffffffffP1023 // hex constant
DBL_MAX_10_EXP+308
If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits ofprecision), then DECIMAL_DIG would be 21.

Forward references:conditional inclusion (6.10.1), complex arithmetic<complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>(7.24), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>(7.20), input/output <stdio.h> (7.19), mathematics <math.h> (7.12).

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6. Language
6.1 Notation
1

In the syntax notation used in this clause, syntactic categories (nonterminals) areindicated by italic type, and literal words and character set members (terminals) by bold
type. A colon (:) following a nonterminal introduces its definition. Alternative
definitions are listed on separate lines, except when prefaced by the words ‘‘one of’’. An
optional symbol is indicated by the subscript ‘‘opt’’, so that{ expressionopt }indicates an optional expression enclosed in braces.

2

When syntactic categories are referred to in the main text, they are not italicized andwords are separated by spaces instead of hyphens.

3

A summary of the language syntax is given in annex A.

6.2 Concepts
6.2.1 Scopes of identifiers
1

An identifier can denote an object; a function; a tag or a member of a structure, union, or
enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
same identifier can denote different entities at different points in the program. A memberof an enumeration is called an enumeration constant. Macro names and macroparameters are not considered further here, because prior to the semantic phase of
program translation any occurrences of macro names in the source file are replaced by the
preprocessing token sequences that constitute their macro definitions.

2

For each different entity that an identifier designates, the identifier is visible (i.e., can beused) only within a region of program text called its scope. Different entities designatedby the same identifier either have different scopes, or are in different name spaces. There
are four kinds of scopes: function, file, block, and function prototype. (A function
prototype is a declaration of a function that declares the types of its parameters.)

3

A label name is the only kind of identifier that has function scope. It can be used (in agoto statement) anywhere in the function in which it appears, and is declared implicitly
by its syntactic appearance (followed by a : and a statement).

4

Every other identifier has scope determined by the placement of its declaration (in adeclarator or type specifier). If the declarator or type specifier that declares the identifierappears outside of any block or list of parameters, the identifier has file scope, which
terminates at the end of the translation unit. If the declarator or type specifier thatdeclares the identifier appears inside a block or within the list of parameter declarations ina function definition, the identifier has block scope, which terminates at the end of theassociated block. If the declarator or type specifier that declares the identifier appears§6.2.1

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within the list of parameter declarations in a function prototype (not part of a function
definition), the identifier has function prototype scope, which terminates at the end of thefunction declarator. If an identifier designates two different entities in the same namespace, the scopes might overlap. If so, the scope of one entity (the inner scope) will be astrict subset of the scope of the other entity (the outer scope). Within the inner scope, theidentifier designates the entity declared in the inner scope; the entity declared in the outer
scope is hidden (and not visible) within the inner scope.
5

Unless explicitly stated otherwise, where this International Standard uses the term‘‘identifier’’ to refer to some entity (as opposed to the syntactic construct), it refers to theentity in the relevant name space whose declaration is visible at the point the identifier
occurs.

6

Two identifiers have the same scope if and only if their scopes terminate at the same
point.

7

Structure, union, and enumeration tags have scope that begins just after the appearance ofthe tag in a type specifier that declares the tag. Each enumeration constant has scope thatbegins just after the appearance of its defining enumerator in an enumerator list. Anyother identifier has scope that begins just after the completion of its declarator.
Forward references: declarations (6.7), function calls (6.5.2.2), function definitions(6.9.1), identifiers (6.4.2), name spaces of identifiers (6.2.3), macro replacement (6.10.3),
source file inclusion (6.10.2), statements (6.8).

6.2.2 Linkages of identifiers
1

An identifier declared in different scopes or in the same scope more than once can bemade to refer to the same object or function by a process called linkage.21) There arethree kinds of linkage: external, internal, and none.

2

In the set of translation units and libraries that constitutes an entire program, eachdeclaration of a particular identifier with external linkage denotes the same object orfunction. Within one translation unit, each declaration of an identifier with internal
linkage denotes the same object or function. Each declaration of an identifier with nolinkage denotes a unique entity.

3

If the declaration of a file scope identifier for an object or a function contains the storageclass specifier static, the identifier has internal linkage.22)

4

For an identifier declared with the storage-class specifier extern in a scope in which a21) There is no linkage between different identifiers.
22) A function declaration can contain the storage-class specifier static only if it is at file scope; see
6.7.1.

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prior declaration of that identifier is visible,23) if the prior declaration specifies internal orexternal linkage, the linkage of the identifier at the later declaration is the same as thelinkage specified at the prior declaration. If no prior declaration is visible, or if the priordeclaration specifies no linkage, then the identifier has external linkage.
5

If the declaration of an identifier for a function has no storage-class specifier, its linkage
is determined exactly as if it were declared with the storage-class specifier extern. If
the declaration of an identifier for an object has file scope and no storage-class specifier,its linkage is external.

6

The following identifiers have no linkage: an identifier declared to be anything other thanan object or a function; an identifier declared to be a function parameter; a block scope
identifier for an object declared without the storage-class specifier extern.

7

If, within a translation unit, the same identifier appears with both internal and external
linkage, the behavior is undefined.
Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
statements (6.8).

6.2.3 Name spaces of identifiers
1

If more than one declaration of a particular identifier is visible at any point in atranslation unit, the syntactic context disambiguates uses that refer to different entities.
Thus, there are separate name spaces for various categories of identifiers, as follows:— label names (disambiguated by the syntax of the label declaration and use);— the tags of structures, unions, and enumerations (disambiguated by following any24)of the keywords struct, union, or enum);— the members of structures or unions; each structure or union has a separate namespace for its members (disambiguated by the type of the expression used to access themember via the . or -> operator);— all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
enumeration constants).
Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
(6.7.2.3), the goto statement (6.8.6.1).

23) As specified in 6.2.1, the later declaration might hide the prior declaration.
24) There is only one name space for tags even though three are possible.

§6.2.3

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6.2.4 Storage durations of objects
1

An object has a storage duration that determines its lifetime. There are three storage
durations: static, automatic, and allocated. Allocated storage is described in 7.20.3.

2

The lifetime of an object is the portion of program execution during which storage isguaranteed to be reserved for it. An object exists, has a constant address,25) and retains
its last-stored value throughout its lifetime.26) If an object is referred to outside of its
lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
the object it points to reaches the end of its lifetime.

3

An object whose identifier is declared with external or internal linkage, or with thestorage-class specifier static has static storage duration. Its lifetime is the entire
execution of the program and its stored value is initialized only once, prior to program
startup.

4

An object whose identifier is declared with no linkage and without the storage-classspecifier static has automatic storage duration.

5

For such an object that does not have a variable length array type, its lifetime extends
from entry into the block with which it is associated until execution of that block ends inany way. (Entering an enclosed block or calling a function suspends, but does not end,
execution of the current block.) If the block is entered recursively, a new instance of theobject is created each time. The initial value of the object is indeterminate. If an
initialization is specified for the object, it is performed each time the declaration isreached in the execution of the block; otherwise, the value becomes indeterminate eachtime the declaration is reached.

6

For such an object that does have a variable length array type, its lifetime extends fromthe declaration of the object until execution of the program leaves the scope of thedeclaration.27) If the scope is entered recursively, a new instance of the object is createdeach time. The initial value of the object is indeterminate.
Forward references: statements (6.8), function calls (6.5.2.2), declarators (6.7.5), arraydeclarators (6.7.5.2), initialization (6.7.8).

25) The term ‘‘constant address’’ means that two pointers to the object constructed at possibly different
times will compare equal. The address may be different during two different executions of the same
program.
26) In the case of a volatile object, the last store need not be explicit in the program.
27) Leaving the innermost block containing the declaration, or jumping to a point in that block or anembedded block prior to the declaration, leaves the scope of the declaration.

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6.2.5 Types
1

The meaning of a value stored in an object or returned by a function is determined by thetype of the expression used to access it. (An identifier declared to be an object is thesimplest such expression; the type is specified in the declaration of the identifier.) Types
are partitioned into object types (types that fully describe objects), function types (types
that describe functions), and incomplete types (types that describe objects but lackinformation needed to determine their sizes).

2

An object declared as type _Bool is large enough to store the values 0 and 1.

3

An object declared as type char is large enough to store any member of the basic
execution character set. If a member of the basic execution character set is stored in achar object, its value is guaranteed to be nonnegative. If any other character is stored ina char object, the resulting value is implementation-defined but shall be within the rangeof values that can be represented in that type.

4

There are five standard signed integer types, designated as signed char, shortint, int, long int, and long long int. (These and other types may bedesignated in several additional ways, as described in 6.7.2.) There may also be
implementation-defined extended signed integer types.28) The standard and extended
signed integer types are collectively called signed integer types.29)

5

An object declared as type signed char occupies the same amount of storage as a‘‘plain’’ char object. A ‘‘plain’’ int object has the natural size suggested by thearchitecture of the execution environment (large enough to contain any value in the range
INT_MIN to INT_MAX as defined in the header <limits.h>).

6

For each of the signed integer types, there is a corresponding (but different) unsigned
integer type (designated with the keyword unsigned) that uses the same amount ofstorage (including sign information) and has the same alignment requirements. The type
_Bool and the unsigned integer types that correspond to the standard signed integer
types are the standard unsigned integer types. The unsigned integer types that
correspond to the extended signed integer types are the extended unsigned integer types.
The standard and extended unsigned integer types are collectively called unsigned integer
types.30)

28) Implementation-defined keywords shall have the form of an identifier reserved for any use as
described in 7.1.3.
29) Therefore, any statement in this Standard about signed integer types also applies to the extended
signed integer types.
30) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
unsigned integer types.

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7

The standard signed integer types and standard unsigned integer types are collectively
called the standard integer types, the extended signed integer types and extended
unsigned integer types are collectively called the extended integer types.

8

For any two integer types with the same signedness and different integer conversion rank(see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
subrange of the values of the other type.

9

The range of nonnegative values of a signed integer type is a subrange of thecorresponding unsigned integer type, and the representation of the same value in eachtype is the same.31) A computation involving unsigned operands can never overflow,
because a result that cannot be represented by the resulting unsigned integer type isreduced modulo the number that is one greater than the largest value that can be
represented by the resulting type.

10

There are three real floating types, designated as float, double, and long
double.32) The set of values of the type float is a subset of the set of values of thetype double; the set of values of the type double is a subset of the set of values of thetype long double.

11

There are three complex types, designated as float _Complex, double_Complex, and long double _Complex.33) The real floating and complex types
are collectively called the floating types.

12

For each floating type there is a corresponding real type, which is always a real floating
type. For real floating types, it is the same type. For complex types, it is the type given
by deleting the keyword _Complex from the type name.

13

Each complex type has the same representation and alignment requirements as an array
type containing exactly two elements of the corresponding real type; the first element isequal to the real part, and the second element to the imaginary part, of the complex
number.

14

The type char, the signed and unsigned integer types, and the floating types arecollectively called the basic types. Even if the implementation defines two or more basic
types to have the same representation, they are nevertheless different types.34)
31) The same representation and alignment requirements are meant to imply interchangeability asarguments to functions, return values from functions, and members of unions.
32) See ‘‘future language directions’’ (6.11.1).
33) A specification for imaginary types is in informative annex G.
34) An implementation may define new keywords that provide alternative ways to designate a basic (orany other) type; this does not violate the requirement that all basic types be different.
Implementation-defined keywords shall have the form of an identifier reserved for any use as
described in 7.1.3.

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15

The three types char, signed char, and unsigned char are collectively called
the character types. The implementation shall define char to have the same range,
representation, and behavior as either signed char or unsigned char.35)

16

An enumeration comprises a set of named integer constant values. Each distinct
enumeration constitutes a different enumerated type.

17

The type char, the signed and unsigned integer types, and the enumerated types arecollectively called integer types. The integer and real floating types are collectively called
real types.

18

Integer and floating types are collectively called arithmetic types. Each arithmetic type
belongs to one type domain: the real type domain comprises the real types, the complex
type domain comprises the complex types.

19

The void type comprises an empty set of values; it is an incomplete type that cannot becompleted.

20

Any number of derived types can be constructed from the object, function, andincomplete types, as follows:— An array type describes a contiguously allocated nonempty set of objects with aparticular member object type, called the element type.36) Array types arecharacterized by their element type and by the number of elements in the array. An
array type is said to be derived from its element type, and if its element type is T , thearray type is sometimes called ‘‘array of T ’’. The construction of an array type froman element type is called ‘‘array type derivation’’.
— A structure type describes a sequentially allocated nonempty set of member objects(and, in certain circumstances, an incomplete array), each of which has an optionallyspecified name and possibly distinct type.
— A union type describes an overlapping nonempty set of member objects, each ofwhich has an optionally specified name and possibly distinct type.
— A function type describes a function with specified return type. A function type ischaracterized by its return type and the number and types of its parameters. A
function type is said to be derived from its return type, and if its return type is T , thefunction type is sometimes called ‘‘function returning T ’’. The construction of afunction type from a return type is called ‘‘function type derivation’’.

35) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can beused to distinguish the two options. Irrespective of the choice made, char is a separate type from theother two and is not compatible with either.
36) Since object types do not include incomplete types, an array of incomplete type cannot be constructed.

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WG14/N1256— A pointer type may be derived from a function type, an object type, or an incomplete
type, called the referenced type. A pointer type describes an object whose value
provides a reference to an entity of the referenced type. A pointer type derived fromthe referenced type T is sometimes called ‘‘pointer to T ’’. The construction of apointer type from a referenced type is called ‘‘pointer type derivation’’.
These methods of constructing derived types can be applied recursively.
21

Arithmetic types and pointer types are collectively called scalar types. Array andstructure types are collectively called aggregate types.37)

22

An array type of unknown size is an incomplete type. It is completed, for an identifier ofthat type, by specifying the size in a later declaration (with internal or external linkage).
A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete
type. It is completed, for all declarations of that type, by declaring the same structure orunion tag with its defining content later in the same scope.

23

A type has known constant size if the type is not incomplete and is not a variable length
array type.

24

Array, function, and pointer types are collectively called derived declarator types. A
declarator type derivation from a type T is the construction of a derived declarator typefrom T by the application of an array-type, a function-type, or a pointer-type derivation toT.

25

A type is characterized by its type category, which is either the outermost derivation of a
derived type (as noted above in the construction of derived types), or the type itself if thetype consists of no derived types.

26

Any type so far mentioned is an unqualified type. Each unqualified type has several
qualified versions of its type,38) corresponding to the combinations of one, two, or all
three of the const, volatile, and restrict qualifiers. The qualified or unqualified
versions of a type are distinct types that belong to the same type category and have thesame representation and alignment requirements.39) A derived type is not qualified by thequalifiers (if any) of the type from which it is derived.

27

A pointer to void shall have the same representation and alignment requirements as apointer to a character type.39) Similarly, pointers to qualified or unqualified versions ofcompatible types shall have the same representation and alignment requirements. All

37) Note that aggregate type does not include union type because an object with union type can only
contain one member at a time.
38) See 6.7.3 regarding qualified array and function types.
39) The same representation and alignment requirements are meant to imply interchangeability asarguments to functions, return values from functions, and members of unions.

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pointers to structure types shall have the same representation and alignment requirements
as each other. All pointers to union types shall have the same representation andalignment requirements as each other. Pointers to other types need not have the same
representation or alignment requirements.
28

EXAMPLE 1 The type designated as ‘‘float *’’ has type ‘‘pointer to float’’. Its type category is
pointer, not a floating type. The const-qualified version of this type is designated as ‘‘float * const’’
whereas the type designated as ‘‘const float *’’ is not a qualified type — its type is ‘‘pointer to constqualified float’’ and is a pointer to a qualified type.

29

EXAMPLE 2 The type designated as ‘‘struct tag (*[5])(float)’’ has type ‘‘array of pointer tofunction returning struct tag’’. The array has length five and the function has a single parameter of typefloat. Its type category is array.

Forward references: compatible type and composite type (6.2.7), declarations (6.7).

6.2.6 Representations of types
6.2.6.1 General1

The representations of all types are unspecified except as stated in this subclause.

2

Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
the number, order, and encoding of which are either explicitly specified or
implementation-defined.

3

Values stored in unsigned bit-fields and objects of type unsigned char shall be
represented using a pure binary notation.40)

4

Values stored in non-bit-field objects of any other object type consist of n × CHAR_BIT
bits, where n is the size of an object of that type, in bytes. The value may be copied into
an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes iscalled the object representation of the value. Values stored in bit-fields consist of m bits,
where m is the size specified for the bit-field. The object representation is the set of m
bits the bit-field comprises in the addressable storage unit holding it. Two values (otherthan NaNs) with the same object representation compare equal, but values that compare
equal may have different object representations.

5

Certain object representations need not represent a value of the object type. If the stored
value of an object has such a representation and is read by an lvalue expression that does
not have character type, the behavior is undefined. If such a representation is produced
by a side effect that modifies all or any part of the object by an lvalue expression that
does not have character type, the behavior is undefined.41) Such a representation is called40) A positional representation for integers that uses the binary digits 0 and 1, in which the values
represented by successive bits are additive, begin with 1, and are multiplied by successive integral
powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
CHAR_BIT
type unsigned char range from 0 to 2
− 1.

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a trap representation.
6

When a value is stored in an object of structure or union type, including in a member
object, the bytes of the object representation that correspond to any padding bytes takeunspecified values.42) The value of a structure or union object is never a trap
representation, even though the value of a member of the structure or union object may be
a trap representation.

7

When a value is stored in a member of an object of union type, the bytes of the object
representation that do not correspond to that member but do correspond to other members
take unspecified values.

8

Where an operator is applied to a value that has more than one object representation,
which object representation is used shall not affect the value of the result.43) Where avalue is stored in an object using a type that has more than one object representation forthat value, it is unspecified which representation is used, but a trap representation shallnot be generated.
Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
designators (6.3.2.1).

6.2.6.2 Integer types
1

For unsigned integer types other than unsigned char, the bits of the object
representation shall be divided into two groups: value bits and padding bits (there neednot be any of the latter). If there are N value bits, each bit shall represent a different
power of 2 between 1 and 2 N −1 , so that objects of that type shall be capable ofrepresenting values from 0 to 2 N − 1 using a pure binary representation; this shall beknown as the value representation. The values of any padding bits are unspecified.44)2

For signed integer types, the bits of the object representation shall be divided into threegroups: value bits, padding bits, and the sign bit. There need not be any padding bits;
41) Thus, an automatic variable can be initialized to a trap representation without causing undefined
behavior, but the value of the variable cannot be used until a proper value is stored in it.
42) Thus, for example, structure assignment need not copy any padding bits.

43) It is possible for objects x and y with the same effective type T to have the same value when they areaccessed as objects of type T, but to have different values in other contexts. In particular, if == isdefined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
on values of type T may distinguish between them.
44) Some combinations of padding bits might generate trap representations, for example, if one padding
bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
representation other than as part of an exceptional condition such as an overflow, and this cannot occur
with unsigned types. All other combinations of padding bits are alternative object representations of
the value specified by the value bits.

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there shall be exactly one sign bit. Each bit that is a value bit shall have the same value as
the same bit in the object representation of the corresponding unsigned type (if there are
M value bits in the signed type and N in the unsigned type, then M ≤ N ). If the sign bit
is zero, it shall not affect the resulting value. If the sign bit is one, the value shall be
modified in one of the following ways:— the corresponding value with sign bit 0 is negated (sign and magnitude);— the sign bit has the value −(2 N ) (two’s complement);— the sign bit has the value −(2 N − 1) (ones’ complement ).

Which of these applies is implementation-defined, as is whether the value with sign bit 1
and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones’
complement), is a trap representation or a normal value. In the case of sign andmagnitude and ones’ complement, if this representation is a normal value it is called anegative zero.

3

If the implementation supports negative zeros, they shall be generated only by:— the &, |, ^, ~, <<, and >> operators with arguments that produce such a value;— the +, -, *, /, and % operators where one argument is a negative zero and the result is
zero;— compound assignment operators based on the above cases.
It is unspecified whether these cases actually generate a negative zero or a normal zero,and whether a negative zero becomes a normal zero when stored in an object.

4

If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,and >> operators with arguments that would produce such a value is undefined.

5

The values of any padding bits are unspecified.45) A valid (non-trap) object representationof a signed integer type where the sign bit is zero is a valid object representation of thecorresponding unsigned type, and shall represent the same value. For any integer type,the object representation where all the bits are zero shall be a representation of the value
zero in that type.

6

The precision of an integer type is the number of bits it uses to represent values,
excluding any sign and padding bits. The width of an integer type is the same but
including any sign bit; thus for unsigned integer types the two values are the same, while

45) Some combinations of padding bits might generate trap representations, for example, if one padding
bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
representation other than as part of an exceptional condition such as an overflow. All othercombinations of padding bits are alternative object representations of the value specified by the value
bits.

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for signed integer types the width is one greater than the precision.

6.2.7 Compatible type and composite type1

Two types have compatible type if their types are the same. Additional rules fordetermining whether two types are compatible are described in 6.7.2 for type specifiers,in 6.7.3 for type qualifiers, and in 6.7.5 for declarators.46) Moreover, two structure,
union, or enumerated types declared in separate translation units are compatible if theirtags and members satisfy the following requirements: If one is declared with a tag, theother shall be declared with the same tag. If both are complete types, then the following
additional requirements apply: there shall be a one-to-one correspondence between theirmembers such that each pair of corresponding members are declared with compatible
types, and such that if one member of a corresponding pair is declared with a name, theother member is declared with the same name. For two structures, corresponding
members shall be declared in the same order. For two structures or unions, corresponding
bit-fields shall have the same widths. For two enumerations, corresponding members
shall have the same values.

2

All declarations that refer to the same object or function shall have compatible type;otherwise, the behavior is undefined.

3

A composite type can be constructed from two types that are compatible; it is a type thatis compatible with both of the two types and satisfies the following conditions:— If one type is an array of known constant size, the composite type is an array of thatsize; otherwise, if one type is a variable length array, the composite type is that type.
— If only one type is a function type with a parameter type list (a function prototype),
the composite type is a function prototype with the parameter type list.
— If both types are function types with parameter type lists, the type of each parameterin the composite parameter type list is the composite type of the corresponding
parameters.
These rules apply recursively to the types from which the two types are derived.

4

For an identifier with internal or external linkage declared in a scope in which a priordeclaration of that identifier is visible,47) if the prior declaration specifies internal orexternal linkage, the type of the identifier at the later declaration becomes the composite
type.

46) Two types need not be identical to be compatible.
47) As specified in 6.2.1, the later declaration might hide the prior declaration.

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Given the following two file scope declarations:int f(int (*)(), double (*)[3]);int f(int (*)(char *), double (*)[]);The resulting composite type for the function is:
int f(int (*)(char *), double (*)[3]);§6.2.7

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6.3 Conversions
1

Several operators convert operand values from one type to another automatically. This
subclause specifies the result required from such an implicit conversion, as well as thosethat result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
the conversions performed by most ordinary operators; it is supplemented as required by
the discussion of each operator in 6.5.

2

Conversion of an operand value to a compatible type causes no change to the value or the
representation.
Forward references: cast operators (6.5.4).

6.3.1 Arithmetic operands
6.3.1.1 Boolean, characters, and integers
1Every integer type has an integer conversion rank defined as follows:— No two signed integer types shall have the same rank, even if they have the same
representation.
— The rank of a signed integer type shall be greater than the rank of any signed integer
type with less precision.
— The rank of long long int shall be greater than the rank of long int, whichshall be greater than the rank of int, which shall be greater than the rank of shortint, which shall be greater than the rank of signed char.
— The rank of any unsigned integer type shall equal the rank of the corresponding
signed integer type, if any.
— The rank of any standard integer type shall be greater than the rank of any extended
integer type with the same width.
— The rank of char shall equal the rank of signed char and unsigned char.
— The rank of _Bool shall be less than the rank of all other standard integer types.
— The rank of any enumerated type shall equal the rank of the compatible integer type(see 6.7.2.2).
— The rank of any extended signed integer type relative to another extended signed
integer type with the same precision is implementation-defined, but still subject to theother rules for determining the integer conversion rank.
— For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 hasgreater rank than T3, then T1 has greater rank than T3.

2

The following may be used in an expression wherever an int or unsigned int may
be used:42

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ISO/IEC 9899:TC3— An object or expression with an integer type whose integer conversion rank is lessthan or equal to the rank of int and unsigned int.

— A bit-field of type _Bool, int, signed int, or unsigned int.
If an int can represent all values of the original type, the value is converted to an int;
otherwise, it is converted to an unsigned int. These are called the integer
promotions.48) All other types are unchanged by the integer promotions.
3

The integer promotions preserve value including sign. As discussed earlier, whether a‘‘plain’’ char is treated as signed is implementation-defined.
Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers(6.7.2.1).

6.3.1.2 Boolean type1

When any scalar value is converted to _Bool, the result is 0 if the value compares equal
to 0; otherwise, the result is 1.

6.3.1.3 Signed and unsigned integers
1

When a value with integer type is converted to another integer type other than _Bool, if
the value can be represented by the new type, it is unchanged.

2

Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
subtracting one more than the maximum value that can be represented in the new typeuntil the value is in the range of the new type.49)

3

Otherwise, the new type is signed and the value cannot be represented in it; either the
result is implementation-defined or an implementation-defined signal is raised.

6.3.1.4 Real floating and integer
1

When a finite value of real floating type is converted to an integer type other than _Bool,the fractional part is discarded (i.e., the value is truncated toward zero). If the value ofthe integral part cannot be represented by the integer type, the behavior is undefined.50)

2

When a value of integer type is converted to a real floating type, if the value being
converted can be represented exactly in the new type, it is unchanged. If the value being
converted is in the range of values that can be represented but cannot be represented48) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of theshift operators, as specified by their respective subclauses.
49) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.
50) The remaindering operation performed when a value of integer type is converted to unsigned typeneed not be performed when a value of real floating type is converted to unsigned type. Thus, therange of portable real floating values is (−1, Utype_MAX+1).

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exactly, the result is either the nearest higher or nearest lower representable value, chosen
in an implementation-defined manner. If the value being converted is outside the range ofvalues that can be represented, the behavior is undefined.

6.3.1.5 Real floating types
1

When a float is promoted to double or long double, or a double is promoted
to long double, its value is unchanged (if the source value is represented in the
precision and range of its type).

2

When a double is demoted to float, a long double is demoted to double or
float, or a value being represented in greater precision and range than required by its
semantic type (see 6.3.1.8) is explicitly converted (including to its own type), if the value
being converted can be represented exactly in the new type, it is unchanged. If the value
being converted is in the range of values that can be represented but cannot be
represented exactly, the result is either the nearest higher or nearest lower representablevalue, chosen in an implementation-defined manner. If the value being converted isoutside the range of values that can be represented, the behavior is undefined.

6.3.1.6 Complex types
1

When a value of complex type is converted to another complex type, both the real andimaginary parts follow the conversion rules for the corresponding real types.

6.3.1.7 Real and complex
1

When a value of real type is converted to a complex type, the real part of the complex
result value is determined by the rules of conversion to the corresponding real type andthe imaginary part of the complex result value is a positive zero or an unsigned zero.

2

When a value of complex type is converted to a real type, the imaginary part of thecomplex value is discarded and the value of the real part is converted according to theconversion rules for the corresponding real type.

6.3.1.8 Usual arithmetic conversions
1

Many operators that expect operands of arithmetic type cause conversions and yield resulttypes in a similar way. The purpose is to determine a common real type for the operands
and result. For the specified operands, each operand is converted, without change of typedomain, to a type whose corresponding real type is the common real type. Unlessexplicitly stated otherwise, the common real type is also the corresponding real type ofthe result, whose type domain is the type domain of the operands if they are the same,and complex otherwise. This pattern is called the usual arithmetic conversions:First, if the corresponding real type of either operand is long double, the otheroperand is converted, without change of type domain, to a type whose
corresponding real type is long double.
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Otherwise, if the corresponding real type of either operand is double, the otheroperand is converted, without change of type domain, to a type whose
corresponding real type is double.
Otherwise, if the corresponding real type of either operand is float, the otheroperand is converted, without change of type domain, to a type whose
corresponding real type is float.51)
Otherwise, the integer promotions are performed on both operands. Then thefollowing rules are applied to the promoted operands:
If both operands have the same type, then no further conversion is needed.
Otherwise, if both operands have signed integer types or both have unsigned
integer types, the operand with the type of lesser integer conversion rank isconverted to the type of the operand with greater rank.
Otherwise, if the operand that has unsigned integer type has rank greater or
equal to the rank of the type of the other operand, then the operand withsigned integer type is converted to the type of the operand with unsigned
integer type.
Otherwise, if the type of the operand with signed integer type can represent
all of the values of the type of the operand with unsigned integer type, thenthe operand with unsigned integer type is converted to the type of theoperand with signed integer type.
Otherwise, both operands are converted to the unsigned integer typecorresponding to the type of the operand with signed integer type.
2

The values of floating operands and of the results of floating expressions may be
represented in greater precision and range than that required by the type; the types are notchanged thereby.52)

51) For example, addition of a double _Complex and a float entails just the conversion of thefloat operand to double (and yields a double _Complex result).
52) The cast and assignment operators are still required to perform their specified conversions as
described in 6.3.1.4 and 6.3.1.5.

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6.3.2 Other operands
6.3.2.1 Lvalues, arrays, and function designators
1

An lvalue is an expression with an object type or an incomplete type other than void;53)
if an lvalue does not designate an object when it is evaluated, the behavior is undefined.
When an object is said to have a particular type, the type is specified by the lvalue used todesignate the object. A modifiable lvalue is an lvalue that does not have array type, does
not have an incomplete type, does not have a const-qualified type, and if it is a structureor union, does not have any member (including, recursively, any member or element of
all contained aggregates or unions) with a const-qualified type.

2

Except when it is the operand of the sizeof operator, the unary & operator, the ++operator, the -- operator, or the left operand of the . operator or an assignment operator,
an lvalue that does not have array type is converted to the value stored in the designatedobject (and is no longer an lvalue). If the lvalue has qualified type, the value has theunqualified version of the type of the lvalue; otherwise, the value has the type of thelvalue. If the lvalue has an incomplete type and does not have array type, the behavior isundefined.

3

Except when it is the operand of the sizeof operator or the unary & operator, or is astring literal used to initialize an array, an expression that has type ‘‘array of type’’ isconverted to an expression with type ‘‘pointer to type’’ that points to the initial element of
the array object and is not an lvalue. If the array object has register storage class, thebehavior is undefined.

4

A function designator is an expression that has function type. Except when it is theoperand of the sizeof operator54) or the unary & operator, a function designator with
type ‘‘function returning type’’ is converted to an expression that has type ‘‘pointer tofunction returning type’’.
Forward references: address and indirection operators (6.5.3.2), assignment operators(6.5.16), common definitions <stddef.h> (7.17), initialization (6.7.8), postfix
increment and decrement operators (6.5.2.4), prefix increment and decrement operators(6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3).

53) The name ‘‘lvalue’’ comes originally from the assignment expression E1 = E2, in which the left
operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an
object ‘‘locator value’’. What is sometimes called ‘‘rvalue’’ is in this International Standard describedas the ‘‘value of an expression’’.
An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary
expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
54) Because this conversion does not occur, the operand of the sizeof operator remains a function
designator and violates the constraint in 6.5.3.4.

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6.3.2.2 void1

The (nonexistent) value of a void expression (an expression that has type void) shall not
be used in any way, and implicit or explicit conversions (except to void) shall not beapplied to such an expression. If an expression of any other type is evaluated as a void
expression, its value or designator is discarded. (A void expression is evaluated for its
side effects.)

6.3.2.3 Pointers
1

A pointer to void may be converted to or from a pointer to any incomplete or object
type. A pointer to any incomplete or object type may be converted to a pointer to voidand back again; the result shall compare equal to the original pointer.

2

For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer tothe q-qualified version of the type; the values stored in the original and converted pointersshall compare equal.

3

An integer constant expression with the value 0, or such an expression cast to typevoid *, is called a null pointer constant.55) If a null pointer constant is converted to apointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
to a pointer to any object or function.

4

Conversion of a null pointer to another pointer type yields a null pointer of that type.
Any two null pointers shall compare equal.

5

An integer may be converted to any pointer type. Except as previously specified, theresult is implementation-defined, might not be correctly aligned, might not point to anentity of the referenced type, and might be a trap representation.56)

6

Any pointer type may be converted to an integer type. Except as previously specified, theresult is implementation-defined. If the result cannot be represented in the integer type,the behavior is undefined. The result need not be in the range of values of any integer
type.

7

A pointer to an object or incomplete type may be converted to a pointer to a different
object or incomplete type. If the resulting pointer is not correctly aligned57) for the
pointed-to type, the behavior is undefined. Otherwise, when converted back again, theresult shall compare equal to the original pointer. When a pointer to an object is55) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.17.
56) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended tobe consistent with the addressing structure of the execution environment.
57) In general, the concept ‘‘correctly aligned’’ is transitive: if a pointer to type A is correctly aligned for apointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A iscorrectly aligned for a pointer to type C.

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converted to a pointer to a character type, the result points to the lowest addressed byte of
the object. Successive increments of the result, up to the size of the object, yield pointersto the remaining bytes of the object.
8

A pointer to a function of one type may be converted to a pointer to a function of anothertype and back again; the result shall compare equal to the original pointer. If a converted
pointer is used to call a function whose type is not compatible with the pointed-to type,the behavior is undefined.
Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
capable of holding object pointers (7.18.1.4), simple assignment (6.5.16.1).

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6.4 Lexical elements
Syntax1

token:
keywordidentifier
constant
string-literalpunctuator
preprocessing-token:
header-nameidentifier
pp-numbercharacter-constantstring-literalpunctuator
each non-white-space character that cannot be one of the above
Constraints

2

Each preprocessing token that is converted to a token shall have the lexical form of a
keyword, an identifier, a constant, a string literal, or a punctuator.
Semantics

3

A token is the minimal lexical element of the language in translation phases 7 and 8. The
categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
A preprocessing token is the minimal lexical element of the language in translation
phases 3 through 6. The categories of preprocessing tokens are: header names,
identifiers, preprocessing numbers, character constants, string literals, punctuators, andsingle non-white-space characters that do not lexically match the other preprocessing
token categories.58) If a ' or a " character matches the last category, the behavior isundefined. Preprocessing tokens can be separated by white space; this consists ofcomments (described later), or white-space characters (space, horizontal tab, new-line,
vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
during translation phase 4, white space (or the absence thereof) serves as more than
preprocessing token separation. White space may appear within a preprocessing token
only as part of a header name or between the quotation characters in a character constantor string literal.

58) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
occur in source files.

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4

If the input stream has been parsed into preprocessing tokens up to a given character, thenext preprocessing token is the longest sequence of characters that could constitute a
preprocessing token. There is one exception to this rule: header name preprocessing
tokens are recognized only within #include preprocessing directives and in
implementation-defined locations within #pragma directives. In such contexts, asequence of characters that could be either a header name or a string literal is recognized
as the former.

5

EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not avalid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the programfragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
not E is a macro name.

6

EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
increment operators, even though the parse x ++ + ++ y might yield a correct expression.

Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
increment and decrement operators (6.5.2.4), prefix increment and decrement operators(6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals(6.4.5).

6.4.1 Keywords
Syntax1

keyword: one of
auto
break
case
char
const
continuedefaultdodoubleelse

enum
extern
float
for
goto
if
inlineint
longregister

restrictreturnshort
signedsizeofstaticstructswitchtypedefunion

unsigned
void
volatile
while
_Bool
_Complex_Imaginary

Semantics
2

The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
keywords, and shall not be used otherwise. The keyword _Imaginary is reserved forspecifying imaginary types.59)59) One possible specification for imaginary types appears in annex G.

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6.4.2 Identifiers
6.4.2.1 General
Syntax1

identifier:identifier-nondigit
identifier identifier-nondigit
identifier digit
identifier-nondigit:
nondigit
universal-character-nameother implementation-defined charactersnondigit: one of
_ a b
n o
A B
N O

c
p
C
P

d
q
D
Q

e
r
E
R

f
s
F
S

g
t
G
T

h
u
H
U

i
v
I
V

digit: one of
0 1

3

4

5

6

7

8

9

2

j
w
J
W

k
x
K
X

l
y
L
Y

m
z
M
Z

Semantics
2

An identifier is a sequence of nondigit characters (including the underscore _, thelowercase and uppercase Latin letters, and other characters) and digits, which designates
one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
There is no specific limit on the maximum length of an identifier.

3

Each universal character name in an identifier shall designate a character whose encodingin ISO/IEC 10646 falls into one of the ranges specified in annex D.60) The initialcharacter shall not be a universal character name designating a digit. An implementation
may allow multibyte characters that are not part of the basic source character set toappear in identifiers; which characters and their correspondence to universal characternames is implementation-defined.

4

When preprocessing tokens are converted to tokens during translation phase 7, if apreprocessing token could be converted to either a keyword or an identifier, it is converted
to a keyword.

60) On systems in which linkers cannot accept extended characters, an encoding of the universal charactername may be used in forming valid external identifiers. For example, some otherwise unusedcharacter or sequence of characters may be used to encode the \u in a universal character name.
Extended characters may produce a long external identifier.

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Implementation limits
5

As discussed in 5.2.4.1, an implementation may limit the number of significant initialcharacters in an identifier; the limit for an external name (an identifier that has external
linkage) may be more restrictive than that for an internal name (a macro name or an
identifier that does not have external linkage). The number of significant characters in an
identifier is implementation-defined.

6

Any identifiers that differ in a significant character are different identifiers. If two
identifiers differ only in nonsignificant characters, the behavior is undefined.
Forward references: universal character names (6.4.3), macro replacement (6.10.3).

6.4.2.2 Predefined identifiers
Semantics
1

The identifier _ _func_ _ shall be implicitly declared by the translator as if,
immediately following the opening brace of each function definition, the declaration
static const char _ _func_ _[] = "function-name";
appeared, where function-name is the name of the lexically-enclosing function.61)

2This name is encoded as if the implicit declaration had been written in the source
character set and then translated into the execution character set as indicated in translation
phase 5.

3

EXAMPLE

Consider the code fragment:#include <stdio.h>void myfunc(void){
printf("%s\n", _ _func_ _);/* ... */}Each time the function is called, it will print to the standard output stream:
myfuncForward references: function definitions (6.9.1).

61) Since the name _ _func_ _ is reserved for any use by the implementation (7.1.3), if any otheridentifier is explicitly declared using the name _ _func_ _, the behavior is undefined.

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6.4.3 Universal character names
Syntax1

universal-character-name:\u hex-quad\U hex-quad hex-quad
hex-quad:
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit
Constraints

2

A universal character name shall not specify a character whose short identifier is less than
00A0 other than 0024 ($), 0040 (@), or 0060 (‘), nor one in the range D800 through
DFFF inclusive.62)
Description

3

Universal character names may be used in identifiers, character constants, and string
literals to designate characters that are not in the basic character set.
Semantics

4

The universal character name \Unnnnnnnn designates the character whose eight-digit
short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.63) Similarly, the universal
character name \unnnn designates the character whose four-digit short identifier is nnnn
(and whose eight-digit short identifier is 0000nnnn).

62) The disallowed characters are the characters in the basic character set and the code positions reserved
by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
UTF−16).
63) Short identifiers for characters were first specified in ISO/IEC 10646−1/AMD9:1997.

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6.4.4 Constants
Syntax1

constant:
integer-constantfloating-constantenumeration-constantcharacter-constant
Constraints

2

Each constant shall have a type and the value of a constant shall be in the range ofrepresentable values for its type.

Semantics
3

Each constant has a type, determined by its form and value, as detailed later.

6.4.4.1 Integer constants
Syntax1

integer-constant:decimal-constant integer-suffixopt
octal-constant integer-suffixopt
hexadecimal-constant integer-suffixopt
decimal-constant:nonzero-digit
decimal-constant digit
octal-constant:0octal-constant octal-digit
hexadecimal-constant:hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit
hexadecimal-prefix: one of
0x 0X

54

nonzero-digit: one of
1 2 3 4

5

6

7

8

octal-digit: one of
0 1 2 3

4

5

6

7

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hexadecimal-digit: one of
0 1 2 3 4a b c d e
A B C D E

5
f
F

6

7

8

ISO/IEC 9899:TC3

9integer-suffix:
unsigned-suffix long-suffixopt
unsigned-suffix long-long-suffix
long-suffix unsigned-suffixopt
long-long-suffix unsigned-suffixopt
unsigned-suffix: one ofu U
long-suffix: one ofl L
long-long-suffix: one ofll LL
Description
2

An integer constant begins with a digit, but has no period or exponent part. It may have aprefix that specifies its base and a suffix that specifies its type.

3

A decimal constant begins with a nonzero digit and consists of a sequence of decimal
digits. An octal constant consists of the prefix 0 optionally followed by a sequence of thedigits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
10 through 15 respectively.
Semantics

4

The value of a decimal constant is computed base 10; that of an octal constant, base 8;
that of a hexadecimal constant, base 16. The lexically first digit is the most significant.

5

The type of an integer constant is the first of the corresponding list in which its value canbe represented.

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Octal or Hexadecimal
Constantnone

intlong int
long long int

int
unsigned int
long int
unsigned long int
long long int
unsigned long long int

u or U

unsigned int
unsigned long int
unsigned long long int

unsigned int
unsigned long int
unsigned long long int

l or L

long int
long long int

long int
unsigned long int
long long int
unsigned long long int

Both u or U
and l or L

unsigned long int
unsigned long long int

unsigned long int
unsigned long long int

ll or LL

long long int

long long int
unsigned long long int

Both u or U
and ll or LL

unsigned long long int

unsigned long long int

If an integer constant cannot be represented by any type in its list, it may have an
extended integer type, if the extended integer type can represent its value. If all of thetypes in the list for the constant are signed, the extended integer type shall be signed. If
all of the types in the list for the constant are unsigned, the extended integer type shall be
unsigned. If the list contains both signed and unsigned types, the extended integer typemay be signed or unsigned. If an integer constant cannot be represented by any type in
its list and has no extended integer type, then the integer constant has no type.

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6.4.4.2 Floating constants
Syntax1

floating-constant:decimal-floating-constanthexadecimal-floating-constantdecimal-floating-constant:fractional-constant exponent-partopt floating-suffixopt
digit-sequence exponent-part floating-suffixopt
hexadecimal-floating-constant:hexadecimal-prefix hexadecimal-fractional-constantbinary-exponent-part floating-suffixopt
hexadecimal-prefix hexadecimal-digit-sequencebinary-exponent-part floating-suffixopt
fractional-constant:digit-sequenceopt . digit-sequence
digit-sequence .
exponent-part:e signopt digit-sequence
E signopt digit-sequence
sign: one of+ digit-sequence:
digit
digit-sequence digit
hexadecimal-fractional-constant:hexadecimal-digit-sequenceopt .
hexadecimal-digit-sequence
hexadecimal-digit-sequence .
binary-exponent-part:p signopt digit-sequence
P signopt digit-sequence
hexadecimal-digit-sequence:
hexadecimal-digit
hexadecimal-digit-sequence hexadecimal-digit
floating-suffix: one off l F L§6.4.4.2

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Description
2

A floating constant has a significand part that may be followed by an exponent part and a
suffix that specifies its type. The components of the significand part may include a digit
sequence representing the whole-number part, followed by a period (.), followed by adigit sequence representing the fraction part. The components of the exponent part are ane, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
Either the whole-number part or the fraction part has to be present; for decimal floating
constants, either the period or the exponent part has to be present.
Semantics

3

The significand part is interpreted as a (decimal or hexadecimal) rational number; thedigit sequence in the exponent part is interpreted as a decimal integer. For decimal
floating constants, the exponent indicates the power of 10 by which the significand part isto be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
by which the significand part is to be scaled. For decimal floating constants, and also forhexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
the nearest representable value, or the larger or smaller representable value immediately
adjacent to the nearest representable value, chosen in an implementation-defined manner.
For hexadecimal floating constants when FLT_RADIX is a power of 2, the result iscorrectly rounded.

4

An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
type float. If suffixed by the letter l or L, it has type long double.

5

Floating constants are converted to internal format as if at translation-time. The
conversion of a floating constant shall not raise an exceptional condition or a floatingpoint exception at execution time.
Recommended practice6

The implementation should produce a diagnostic message if a hexadecimal constantcannot be represented exactly in its evaluation format; the implementation should thenproceed with the translation of the program.

7

The translation-time conversion of floating constants should match the execution-time
conversion of character strings by library functions, such as strtod, given matching
inputs suitable for both conversions, the same result format, and default execution-timerounding.64)

64) The specification for the library functions recommends more accurate conversion than required for
floating constants (see 7.20.1.3).

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6.4.4.3 Enumeration constants
Syntax1

enumeration-constant:identifier
Semantics

2

An identifier declared as an enumeration constant has type int.
Forward references: enumeration specifiers (6.7.2.2).

6.4.4.4 Character constants
Syntax1

character-constant:' c-char-sequence 'L' c-char-sequence 'c-char-sequence:c-charc-char-sequence c-charc-char:any member of the source character set except
the single-quote ', backslash \, or new-line character
escape-sequence
escape-sequence:
simple-escape-sequenceoctal-escape-sequence
hexadecimal-escape-sequence
universal-character-namesimple-escape-sequence: one of\' \" \? \\\a \b \f \n \r\t\v

octal-escape-sequence:\ octal-digit\ octal-digit octal-digit\ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence:\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit§6.4.4.4

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Description
2

An integer character constant is a sequence of one or more multibyte characters enclosed
in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by theletter L. With a few exceptions detailed later, the elements of the sequence are any
members of the source character set; they are mapped in an implementation-definedmanner to members of the execution character set.

3

The single-quote ', the double-quote ", the question-mark ?, the backslash \, andarbitrary integer values are representable according to the following table of escapesequences:
single quote 'double quote "question mark ?
backslash \octal character
hexadecimal character

\'
\"
\?
\\
\octal digits\x hexadecimal digits

4

The double-quote " and question-mark ? are representable either by themselves or by theescape sequences \" and \?, respectively, but the single-quote ' and the backslash \shall be represented, respectively, by the escape sequences \' and \\.

5

The octal digits that follow the backslash in an octal escape sequence are taken to be partof the construction of a single character for an integer character constant or of a single
wide character for a wide character constant. The numerical value of the octal integer soformed specifies the value of the desired character or wide character.

6

The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escapesequence are taken to be part of the construction of a single character for an integer
character constant or of a single wide character for a wide character constant. The
numerical value of the hexadecimal integer so formed specifies the value of the desired
character or wide character.

7

Each octal or hexadecimal escape sequence is the longest sequence of characters that canconstitute the escape sequence.

8

In addition, characters not in the basic character set are representable by universal
character names and certain nongraphic characters are representable by escape sequences
consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
and \v.65)

65) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
the result is not a token and a diagnostic is required. See ‘‘future language directions’’ (6.11.4).

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Constraints
9

The value of an octal or hexadecimal escape sequence shall be in the range ofrepresentable values for the type unsigned char for an integer character constant, orthe unsigned type corresponding to wchar_t for a wide character constant.
Semantics

10

An integer character constant has type int. The value of an integer character constantcontaining a single character that maps to a single-byte execution character is thenumerical value of the representation of the mapped character interpreted as an integer.
The value of an integer character constant containing more than one character (e.g.,'ab'), or containing a character or escape sequence that does not map to a single-byte
execution character, is implementation-defined. If an integer character constant contains
a single character or escape sequence, its value is the one that results when an object with
type char whose value is that of the single character or escape sequence is converted totype int.

11

A wide character constant has type wchar_t, an integer type defined in the<stddef.h> header. The value of a wide character constant containing a single
multibyte character that maps to a member of the extended execution character set is thewide character corresponding to that multibyte character, as defined by the mbtowc
function, with an implementation-defined current locale. The value of a wide character
constant containing more than one multibyte character, or containing a multibyte
character or escape sequence not represented in the extended execution character set, isimplementation-defined.

12
13

EXAMPLE 1

The construction '\0' is commonly used to represent the null character.

EXAMPLE 2 Consider implementations that use two’s-complement representation for integers and eightbits for objects that have type char. In an implementation in which type char has the same range ofvalues as signed char, the integer character constant '\xFF' has the value −1; if type char has thesame range of values as unsigned char, the character constant '\xFF' has the value +255.

14

EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
specifies an integer character constant containing only one character, since a hexadecimal escape sequenceis terminated only by a non-hexadecimal character. To specify an integer character constant containing thetwo characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
escape sequence is terminated after three octal digits. (The value of this two-character integer character
constant is implementation-defined.)

15

EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
L'\1234' specifies the implementation-defined value that results from the combination of the values
0123 and '4'.

Forward references: common definitions <stddef.h> (7.17), the mbtowc function(7.20.7.2).

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6.4.5 String literals
Syntax1

string-literal:" s-char-sequenceopt "L" s-char-sequenceopt "s-char-sequence:s-chars-char-sequence s-chars-char:any member of the source character set except
the double-quote ", backslash \, or new-line character
escape-sequence
Description

2

A character string literal is a sequence of zero or more multibyte characters enclosed indouble-quotes, as in "xyz". A wide string literal is the same, except prefixed by theletter L.

3

The same considerations apply to each element of the sequence in a character string
literal or a wide string literal as if it were in an integer character constant or a wide
character constant, except that the single-quote ' is representable either by itself or by theescape sequence \', but the double-quote " shall be represented by the escape sequence\".
Semantics

4

In translation phase 6, the multibyte character sequences specified by any sequence ofadjacent character and wide string literal tokens are concatenated into a single multibyte
character sequence. If any of the tokens are wide string literal tokens, the resulting
multibyte character sequence is treated as a wide string literal; otherwise, it is treated as acharacter string literal.

5

In translation phase 7, a byte or code of value zero is appended to each multibyte
character sequence that results from a string literal or literals.66) The multibyte character
sequence is then used to initialize an array of static storage duration and length justsufficient to contain the sequence. For character string literals, the array elements havetype char, and are initialized with the individual bytes of the multibyte character
sequence; for wide string literals, the array elements have type wchar_t, and are
initialized with the sequence of wide characters corresponding to the multibyte character66) A character string literal need not be a string (see 7.1.1), because a null character may be embedded in
it by a \0 escape sequence.

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sequence, as defined by the mbstowcs function with an implementation-defined current
locale. The value of a string literal containing a multibyte character or escape sequence
not represented in the execution character set is implementation-defined.
6

It is unspecified whether these arrays are distinct provided their elements have theappropriate values. If the program attempts to modify such an array, the behavior isundefined.

7

EXAMPLEThis pair of adjacent character string literals"\x12" "3"
produces a single character string literal containing the two characters whose values are '\x12' and '3',
because escape sequences are converted into single members of the execution character set just prior to
adjacent string literal concatenation.

Forward references: common definitions <stddef.h> (7.17), the mbstowcs
function (7.20.8.1).

6.4.6 Punctuators
Syntax1punctuator: one of[ ] ( ) { } . ->++ -- & * + - ~ !
/ % << >> < > <= >=? : ; ...
= *= /= %= += -= <<=, # ##<: :> <% %> %: %:%:

==

!=

>>=

&=

^

|

&&

^=

|=

||

Semantics
2

A punctuator is a symbol that has independent syntactic and semantic significance.
Depending on context, it may specify an operation to be performed (which in turn may
yield a value or a function designator, produce a side effect, or some combination thereof)
in which case it is known as an operator (other forms of operator also exist in somecontexts). An operand is an entity on which an operator acts.

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In all aspects of the language, the six tokens67)
<:

:>

<%

%>

%:

%:%:

behave, respectively, the same as the six tokens
[

]

{

}

#

##

except for their spelling.68)
Forward references: expressions (6.5), declarations (6.7), preprocessing directives(6.10), statements (6.8).

6.4.7 Header names
Syntax1

header-name:< h-char-sequence >" q-char-sequence "h-char-sequence:h-charh-char-sequence h-charh-char:any member of the source character set except
the new-line character and >q-char-sequence:q-charq-char-sequence q-charq-char:any member of the source character set except
the new-line character and "Semantics

2

The sequences in both forms of header names are mapped in an implementation-definedmanner to headers or external source file names as specified in 6.10.2.

3

If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the67) These tokens are sometimes called ‘‘digraphs’’.
68) Thus [ and <: behave differently when ‘‘stringized’’ (see 6.10.3.2), but can otherwise be freely
interchanged.

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sequence between the " delimiters, the behavior is undefined.69) Header namepreprocessing tokens are recognized only within #include preprocessing directives andin implementation-defined locations within #pragma directives.70)

4

EXAMPLEThe following sequence of characters:

0x3<1/a.h>1e2#include <1/a.h>#define const.member@$forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
by a { on the left and a } on the right).
{0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}{#}{include} {<1/a.h>}{#}{define} {const}{.}{member}{@}{$}

Forward references: source file inclusion (6.10.2).

6.4.8 Preprocessing numbers
Syntax1

pp-number:digit. digitpp-number digit
pp-number identifier-nondigit
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
Description

2

A preprocessing number begins with a digit optionally preceded by a period (.) and may
be followed by valid identifier characters and the character sequences e+, e-, E+, E-,p+, p-, P+, or P-.

3

Preprocessing number tokens lexically include all floating and integer constant tokens.
Semantics

4

A preprocessing number does not have type or a value; it acquires both after a successful
conversion (as part of translation phase 7) to a floating constant token or an integer
constant token.
69) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
70) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.

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6.4.9 Comments
1

Except within a character constant, a string literal, or a comment, the characters /*introduce a comment. The contents of such a comment are examined only to identify
multibyte characters and to find the characters */ that terminate it.71)

2

Except within a character constant, a string literal, or a comment, the characters //introduce a comment that includes all multibyte characters up to, but not including, thenext new-line character. The contents of such a comment are examined only to identify
multibyte characters and to find the terminating new-line character.

3

EXAMPLE"a//b"#include "//e"// */f = g/**//h;
//\
i();
/\
/ j();#define glue(x,y) x##yglue(/,/) k();/*//*/ l();m = n//**/o+ p;// four-character string literal// undefined behavior// comment, not syntax error// equivalent to f = g / h;// part of a two-line comment// part of a two-line comment// syntax error, not comment// equivalent to l();// equivalent to m = n + p;71) Thus, /* ... */ comments do not nest.

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6.5 Expressions
1

An expression is a sequence of operators and operands that specifies computation of avalue, or that designates an object or a function, or that generates side effects, or that
performs a combination thereof.

2

Between the previous and next sequence point an object shall have its stored value
modified at most once by the evaluation of an expression.72) Furthermore, the prior value
shall be read only to determine the value to be stored.73)

3

The grouping of operators and operands is indicated by the syntax.74) Except as specified
later (for the function-call (), &&, ||, ?:, and comma operators), the order of evaluationof subexpressions and the order in which side effects take place are both unspecified.

4

Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,collectively described as bitwise operators) are required to have operands that haveinteger type. These operators yield values that depend on the internal representations ofintegers, and have implementation-defined and undefined aspects for signed types.

5

If an exceptional condition occurs during the evaluation of an expression (that is, if theresult is not mathematically defined or not in the range of representable values for itstype), the behavior is undefined.

6

The effective type of an object for an access to its stored value is the declared type of theobject, if any.75) If a value is stored into an object having no declared type through anlvalue having a type that is not a character type, then the type of the lvalue becomes the72) A floating-point status flag is not an object and can be set more than once within an expression.
73) This paragraph renders undefined statement expressions such asi = ++i + 1;a[i++] = i;while allowing
i = i + 1;
a[i] = i;74) The syntax specifies the precedence of operators in the evaluation of an expression, which is the sameas the order of the major subclauses of this subclause, highest precedence first. Thus, for example, theexpressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators(6.5.3), and an operand contained between any of the following pairs of operators: grouping
parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), andthe conditional operator ?: (6.5.15).
Within each major subclause, the operators have the same precedence. Left- or right-associativity is
indicated in each subclause by the syntax for the expressions discussed therein.
75) Allocated objects have no declared type.

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effective type of the object for that access and for subsequent accesses that do not modify
the stored value. If a value is copied into an object having no declared type using
memcpy or memmove, or is copied as an array of character type, then the effective typeof the modified object for that access and for subsequent accesses that do not modify thevalue is the effective type of the object from which the value is copied, if it has one. For
all other accesses to an object having no declared type, the effective type of the object issimply the type of the lvalue used for the access.
7

An object shall have its stored value accessed only by an lvalue expression that has one of
the following types:76)— a type compatible with the effective type of the object,— a qualified version of a type compatible with the effective type of the object,— a type that is the signed or unsigned type corresponding to the effective type of theobject,— a type that is the signed or unsigned type corresponding to a qualified version of theeffective type of the object,— an aggregate or union type that includes one of the aforementioned types among its
members (including, recursively, a member of a subaggregate or contained union), or— a character type.

8

A floating expression may be contracted, that is, evaluated as though it were an atomic
operation, thereby omitting rounding errors implied by the source code and theexpression evaluation method.77) The FP_CONTRACT pragma in <math.h> provides away to disallow contracted expressions. Otherwise, whether and how expressions arecontracted is implementation-defined.78)
Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.21.2).

76) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
77) A contracted expression might also omit the raising of floating-point exceptions.
78) This license is specifically intended to allow implementations to exploit fast machine instructions thatcombine multiple C operators. As contractions potentially undermine predictability, and can evendecrease accuracy for containing expressions, their use needs to be well-defined and clearly
documented.

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6.5.1 Primary expressions
Syntax1

primary-expression:
identifier
constant
string-literal( expression )Semantics

2

An identifier is a primary expression, provided it has been declared as designating an
object (in which case it is an lvalue) or a function (in which case it is a function
designator).79)

3

A constant is a primary expression. Its type depends on its form and value, as detailed in
6.4.4.

4

A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.

5

A parenthesized expression is a primary expression. Its type and value are identical tothose of the unparenthesized expression. It is an lvalue, a function designator, or a void
expression if the unparenthesized expression is, respectively, an lvalue, a function
designator, or a void expression.
Forward references: declarations (6.7).

6.5.2 Postfix operators
Syntax1

postfix-expression:
primary-expression
postfix-expression [ expression ]postfix-expression ( argument-expression-listopt )postfix-expression . identifier
postfix-expression -> identifier
postfix-expression ++postfix-expression -( type-name ) { initializer-list }( type-name ) { initializer-list , }79) Thus, an undeclared identifier is a violation of the syntax.

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argument-expression-list:
assignment-expression
argument-expression-list , assignment-expression

6.5.2.1 Array subscripting
Constraints
1

One of the expressions shall have type ‘‘pointer to object type’’, the other expression shallhave integer type, and the result has type ‘‘type’’.
Semantics

2

A postfix expression followed by an expression in square brackets [] is a subscripted
designation of an element of an array object. The definition of the subscript operator []is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
apply to the binary + operator, if E1 is an array object (equivalently, a pointer to theinitial element of an array object) and E2 is an integer, E1[E2] designates the E2-thelement of E1 (counting from zero).

3

Successive subscript operators designate an element of a multidimensional array object.
If E is an n-dimensional array (n ≥ 2) with dimensions i × j × . . . × k, then E (used asother than an lvalue) is converted to a pointer to an (n − 1)-dimensional array withdimensions j × . . . × k. If the unary * operator is applied to this pointer explicitly, or
implicitly as a result of subscripting, the result is the pointed-to (n − 1)-dimensional array,
which itself is converted into a pointer if used as other than an lvalue. It follows from thisthat arrays are stored in row-major order (last subscript varies fastest).

4

EXAMPLE

Consider the array object defined by the declaration

int x[3][5];Here x is a 3 × 5 array of ints; more precisely, x is an array of three element objects, each of which is anarray of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted toa pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptuallyentails multiplying i by the size of the object to which the pointer points, namely an array of five int
objects. The results are added and indirection is applied to yield an array of five ints. When used in theexpression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]yields an int.

Forward references: additive operators (6.5.6), address and indirection operators(6.5.3.2), array declarators (6.7.5.2).

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6.5.2.2 Function calls
Constraints
1

The expression that denotes the called function80) shall have type pointer to function
returning void or returning an object type other than an array type.

2

If the expression that denotes the called function has a type that includes a prototype, thenumber of arguments shall agree with the number of parameters. Each argument shallhave a type such that its value may be assigned to an object with the unqualified versionof the type of its corresponding parameter.
Semantics

3

A postfix expression followed by parentheses () containing a possibly empty, commaseparated list of expressions is a function call. The postfix expression denotes the called
function. The list of expressions specifies the arguments to the function.

4

An argument may be an expression of any object type. In preparing for the call to afunction, the arguments are evaluated, and each parameter is assigned the value of thecorresponding argument.81)

5

If the expression that denotes the called function has type pointer to function returning an
object type, the function call expression has the same type as that object type, and has thevalue determined as specified in 6.8.6.4. Otherwise, the function call has type void. If
an attempt is made to modify the result of a function call or to access it after the next
sequence point, the behavior is undefined.

6

If the expression that denotes the called function has a type that does not include a
prototype, the integer promotions are performed on each argument, and arguments thathave type float are promoted to double. These are called the default argument
promotions. If the number of arguments does not equal the number of parameters, thebehavior is undefined. If the function is defined with a type that includes a prototype, andeither the prototype ends with an ellipsis (, ...) or the types of the arguments after
promotion are not compatible with the types of the parameters, the behavior is undefined.
If the function is defined with a type that does not include a prototype, and the types of
the arguments after promotion are not compatible with those of the parameters after
promotion, the behavior is undefined, except for the following cases:80) Most often, this is the result of converting an identifier that is a function designator.
81) A function may change the values of its parameters, but these changes cannot affect the values of thearguments. On the other hand, it is possible to pass a pointer to an object, and the function may
change the value of the object pointed to. A parameter declared to have array or function type isadjusted to have a pointer type as described in 6.9.1.

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WG14/N1256— one promoted type is a signed integer type, the other promoted type is thecorresponding unsigned integer type, and the value is representable in both types;— both types are pointers to qualified or unqualified versions of a character type orvoid.
7

If the expression that denotes the called function has a type that does include a prototype,the arguments are implicitly converted, as if by assignment, to the types of thecorresponding parameters, taking the type of each parameter to be the unqualified versionof its declared type. The ellipsis notation in a function prototype declarator causes
argument type conversion to stop after the last declared parameter. The default argument
promotions are performed on trailing arguments.

8

No other conversions are performed implicitly; in particular, the number and types ofarguments are not compared with those of the parameters in a function definition that
does not include a function prototype declarator.

9

If the function is defined with a type that is not compatible with the type (of theexpression) pointed to by the expression that denotes the called function, the behavior isundefined.

10

The order of evaluation of the function designator, the actual arguments, andsubexpressions within the actual arguments is unspecified, but there is a sequence point
before the actual call.

11

Recursive function calls shall be permitted, both directly and indirectly through any chainof other functions.

12

EXAMPLEIn the function call(*pf[f1()]) (f2(), f3() + f4())
the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
the function pointed to by pf[f1()] is called.

Forward references: function declarators (including prototypes) (6.7.5.3), function
definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).

6.5.2.3 Structure and union members
Constraints
1

The first operand of the . operator shall have a qualified or unqualified structure or union
type, and the second operand shall name a member of that type.

2

The first operand of the -> operator shall have type ‘‘pointer to qualified or unqualified
structure’’ or ‘‘pointer to qualified or unqualified union’’, and the second operand shallname a member of the type pointed to.

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Semantics
3

A postfix expression followed by the . operator and an identifier designates a member ofa structure or union object. The value is that of the named member,82) and is an lvalue if
the first expression is an lvalue. If the first expression has qualified type, the result has
the so-qualified version of the type of the designated member.

4

A postfix expression followed by the -> operator and an identifier designates a memberof a structure or union object. The value is that of the named member of the object towhich the first expression points, and is an lvalue.83) If the first expression is a pointer toa qualified type, the result has the so-qualified version of the type of the designatedmember.

5

One special guarantee is made in order to simplify the use of unions: if a union contains
several structures that share a common initial sequence (see below), and if the union
object currently contains one of these structures, it is permitted to inspect the common
initial part of any of them anywhere that a declaration of the complete type of the union isvisible. Two structures share a common initial sequence if corresponding members havecompatible types (and, for bit-fields, the same widths) for a sequence of one or more
initial members.

6

EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure orunion, f().x is a valid postfix expression but is not an lvalue.

7

EXAMPLE 2

In:

struct s { int i; const int ci; };struct s s;const struct s cs;
volatile struct s vs;the various members have the types:
s.i
s.ci
cs.i
cs.ci
vs.i
vs.ci

int
const int
const int
const int
volatile int
volatile const int82) If the member used to access the contents of a union object is not the same as the member last used tostore a value in the object, the appropriate part of the object representation of the value is reinterpreted
as an object representation in the new type as described in 6.2.6 (a process sometimes called "typepunning"). This might be a trap representation.
83) If &E is a valid pointer expression (where & is the ‘‘address-of ’’ operator, which generates a pointer to
its operand), the expression (&E)->MOS is the same as E.MOS.

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EXAMPLE 3

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The following is a valid fragment:

union {
struct {int
alltypes;} n;struct {
int
type;
int
intnode;} ni;
struct {int
type;
double doublenode;
} nf;
} u;
u.nf.type = 1;
u.nf.doublenode = 3.14;/* ... */if (u.n.alltypes == 1)
if (sin(u.nf.doublenode) == 0.0)/* ... */The following is not a valid fragment (because the union type is not visible within function f):
struct t1 { int m; };struct t2 { int m; };int f(struct t1 *p1, struct t2 *p2){
if (p1->m < 0)
p2->m = -p2->m;return p1->m;}
int g(){
union {
struct t1 s1;
struct t2 s2;} u;/* ... */return f(&u.s1, &u.s2);}

Forward references: address and indirection operators (6.5.3.2), structure and union
specifiers (6.7.2.1).

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6.5.2.4 Postfix increment and decrement operators
Constraints
1

The operand of the postfix increment or decrement operator shall have qualified or
unqualified real or pointer type and shall be a modifiable lvalue.
Semantics

2

The result of the postfix ++ operator is the value of the operand. After the result isobtained, the value of the operand is incremented. (That is, the value 1 of the appropriate
type is added to it.) See the discussions of additive operators and compound assignment
for information on constraints, types, and conversions and the effects of operations on
pointers. The side effect of updating the stored value of the operand shall occur between
the previous and the next sequence point.

3

The postfix -- operator is analogous to the postfix ++ operator, except that the value ofthe operand is decremented (that is, the value 1 of the appropriate type is subtracted fromit).
Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).

6.5.2.5 Compound literals
Constraints
1

The type name shall specify an object type or an array of unknown size, but not a variable
length array type.

2

No initializer shall attempt to provide a value for an object not contained within the entire
unnamed object specified by the compound literal.

3

If the compound literal occurs outside the body of a function, the initializer list shallconsist of constant expressions.
Semantics

4

A postfix expression that consists of a parenthesized type name followed by a braceenclosed list of initializers is a compound literal. It provides an unnamed object whose
value is given by the initializer list.84)

5

If the type name specifies an array of unknown size, the size is determined by the
initializer list as specified in 6.7.8, and the type of the compound literal is that of thecompleted array type. Otherwise (when the type name specifies an object type), the typeof the compound literal is that specified by the type name. In either case, the result is anlvalue.

84) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
or void only, and the result of a cast expression is not an lvalue.

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6

The value of the compound literal is that of an unnamed object initialized by the
initializer list. If the compound literal occurs outside the body of a function, the object
has static storage duration; otherwise, it has automatic storage duration associated withthe enclosing block.

7

All the semantic rules and constraints for initializer lists in 6.7.8 are applicable tocompound literals.85)

8String literals, and compound literals with const-qualified types, need not designatedistinct objects.86)

9EXAMPLE 1

The file scope definition

int *p = (int []){2, 4};initializes p to point to the first element of an array of two ints, the first having the value two and thesecond, four. The expressions in this compound literal are required to be constant. The unnamed object
has static storage duration.

10

EXAMPLE 2

In contrast, invoid f(void){
int *p;/*...*/
p = (int [2]){*p};/*...*/}
p is assigned the address of the first element of an array of two ints, the first having the value previously
pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
unnamed object has automatic storage duration.

11

EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
created using compound literals can be passed to functions without depending on member order:
drawline((struct point){.x=1, .y=1},(struct point){.x=3, .y=4});
Or, if drawline instead expected pointers to struct point:
drawline(&(struct point){.x=1, .y=1},&(struct point){.x=3, .y=4});

12

EXAMPLE 4

A read-only compound literal can be specified through constructions like:(const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}85) For example, subobjects without explicit initializers are initialized to zero.
86) This allows implementations to share storage for string literals and constant compound literals withthe same or overlapping representations.

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13

EXAMPLE 5

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The following three expressions have different meanings:"/tmp/fileXXXXXX"(char []){"/tmp/fileXXXXXX"}(const char []){"/tmp/fileXXXXXX"}
The first always has static storage duration and has type array of char, but need not be modifiable; the last
two have automatic storage duration when they occur within the body of a function, and the first of these
two is modifiable.

14

EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memoryand can even be shared. For example,(const char []){"abc"} == "abc"might yield 1 if the literals’ storage is shared.

15

EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
linked object. For example, there is no way to write a self-referential compound literal that could be usedas the function argument in place of the named object endless_zeros below:
struct int_list { int car; struct int_list *cdr; };struct int_list endless_zeros = {0, &endless_zeros};eval(endless_zeros);

16

EXAMPLE 8

Each compound literal creates only a single object in a given scope:struct s { int i; };int f (void){
struct s *p = 0, *q;
int j = 0;
again:
q = p, p = &((struct s){ j++ });if (j < 2) goto again;
return p == q && q->i == 1;}
The function f() always returns the value 1.

17

Note that if an iteration statement were used instead of an explicit goto and a labeled statement, thelifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
have an indeterminate value, which would result in undefined behavior.

Forward references: type names (6.7.6), initialization (6.7.8).

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6.5.3 Unary operators
Syntax1

unary-expression:
postfix-expression++ unary-expression-- unary-expression
unary-operator cast-expression
sizeof unary-expression
sizeof ( type-name )unary-operator: one of& * + - ~!

6.5.3.1 Prefix increment and decrement operators
Constraints
1

The operand of the prefix increment or decrement operator shall have qualified or
unqualified real or pointer type and shall be a modifiable lvalue.
Semantics2

The value of the operand of the prefix ++ operator is incremented. The result is the newvalue of the operand after incrementation. The expression ++E is equivalent to (E+=1).
See the discussions of additive operators and compound assignment for information on
constraints, types, side effects, and conversions and the effects of operations on pointers.

3

The prefix -- operator is analogous to the prefix ++ operator, except that the value of theoperand is decremented.
Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).

6.5.3.2 Address and indirection operators
Constraints
1

The operand of the unary & operator shall be either a function designator, the result of a[] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
not declared with the register storage-class specifier.

2

The operand of the unary * operator shall have pointer type.
Semantics

3

The unary & operator yields the address of its operand. If the operand has type ‘‘type’’,the result has type ‘‘pointer to type’’. If the operand is the result of a unary * operator,
neither that operator nor the & operator is evaluated and the result is as if both wereomitted, except that the constraints on the operators still apply and the result is not anlvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor

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the unary * that is implied by the [] is evaluated and the result is as if the & operator
were removed and the [] operator were changed to a + operator. Otherwise, the result isa pointer to the object or function designated by its operand.
4

The unary * operator denotes indirection. If the operand points to a function, the result isa function designator; if it points to an object, the result is an lvalue designating theobject. If the operand has type ‘‘pointer to type’’, the result has type ‘‘type’’. If aninvalid value has been assigned to the pointer, the behavior of the unary * operator isundefined.87)
Forward references: storage-class specifiers (6.7.1), structure and union specifiers(6.7.2.1).

6.5.3.3 Unary arithmetic operators
Constraints
1

The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
integer type; of the ! operator, scalar type.
Semantics

2

The result of the unary + operator is the value of its (promoted) operand. The integer
promotions are performed on the operand, and the result has the promoted type.

3

The result of the unary - operator is the negative of its (promoted) operand. The integer
promotions are performed on the operand, and the result has the promoted type.

4

The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,each bit in the result is set if and only if the corresponding bit in the converted operand is
not set). The integer promotions are performed on the operand, and the result has thepromoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
to the maximum value representable in that type minus E.

5

The result of the logical negation operator ! is 0 if the value of its operand comparesunequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
The expression !E is equivalent to (0==E).

87) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It isalways true that if E is a function designator or an lvalue that is a valid operand of the unary &operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name ofan object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, anaddress inappropriately aligned for the type of object pointed to, and the address of an object after theend of its lifetime.

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6.5.3.4 The sizeof operator
Constraints
1

The sizeof operator shall not be applied to an expression that has function type or an
incomplete type, to the parenthesized name of such a type, or to an expression thatdesignates a bit-field member.
Semantics

2

The sizeof operator yields the size (in bytes) of its operand, which may be an
expression or the parenthesized name of a type. The size is determined from the type ofthe operand. The result is an integer. If the type of the operand is a variable length array
type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
integer constant.

3

When applied to an operand that has type char, unsigned char, or signed char,(or a qualified version thereof) the result is 1. When applied to an operand that has array
type, the result is the total number of bytes in the array.88) When applied to an operand
that has structure or union type, the result is the total number of bytes in such an object,including internal and trailing padding.

4

The value of the result is implementation-defined, and its type (an unsigned integer type)is size_t, defined in <stddef.h> (and other headers).

5

EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object toallocate and return a pointer to void. For example:
extern void *alloc(size_t);
double *dp = alloc(sizeof *dp);
The implementation of the alloc function should ensure that its return value is aligned suitably forconversion to a pointer to double.

6

EXAMPLE 2

Another use of the sizeof operator is to compute the number of elements in an array:sizeof array / sizeof array[0]7EXAMPLE 3
function:In this example, the size of a variable length array is computed and returned from a#include <stddef.h>size_t fsize3(int n){char b[n+3];
return sizeof b;}// variable length array// execution time sizeof88) When applied to a parameter declared to have array or function type, the sizeof operator yields thesize of the adjusted (pointer) type (see 6.9.1).

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int main(){size_t size;
size = fsize3(10); // fsize3 returns 13
return 0;}

Forward references: common definitions <stddef.h> (7.17), declarations (6.7),
structure and union specifiers (6.7.2.1), type names (6.7.6), array declarators (6.7.5.2).

6.5.4 Cast operators
Syntax1

cast-expression:
unary-expression( type-name ) cast-expression
Constraints

2

Unless the type name specifies a void type, the type name shall specify qualified or
unqualified scalar type and the operand shall have scalar type.

3

Conversions that involve pointers, other than where permitted by the constraints of
6.5.16.1, shall be specified by means of an explicit cast.
Semantics

4

Preceding an expression by a parenthesized type name converts the value of theexpression to the named type. This construction is called a cast.89) A cast that specifies
no conversion has no effect on the type or value of an expression.

5

If the value of the expression is represented with greater precision or range than requiredby the type named by the cast (6.3.1.8), then the cast specifies a conversion even if thetype of the expression is the same as the named type.

Forward references: equality operators (6.5.9), function declarators (including
prototypes) (6.7.5.3), simple assignment (6.5.16.1), type names (6.7.6).

89) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to theunqualified version of the type.

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6.5.5 Multiplicative operators
Syntax1

multiplicative-expression:
cast-expression
multiplicative-expression * cast-expression
multiplicative-expression / cast-expression
multiplicative-expression % cast-expression
Constraints

2

Each of the operands shall have arithmetic type. The operands of the % operator shallhave integer type.
Semantics

3

The usual arithmetic conversions are performed on the operands.

4

The result of the binary * operator is the product of the operands.

5

The result of the / operator is the quotient from the division of the first operand by thesecond; the result of the % operator is the remainder. In both operations, if the value ofthe second operand is zero, the behavior is undefined.

6

When integers are divided, the result of the / operator is the algebraic quotient with any
fractional part discarded.90) If the quotient a/b is representable, the expression(a/b)*b + a%b shall equal a.

6.5.6 Additive operators
Syntax1

additive-expression:
multiplicative-expression
additive-expression + multiplicative-expression
additive-expression - multiplicative-expression
Constraints

2

For addition, either both operands shall have arithmetic type, or one operand shall be apointer to an object type and the other shall have integer type. (Incrementing isequivalent to adding 1.)

3

For subtraction, one of the following shall hold:— both operands have arithmetic type;90) This is often called ‘‘truncation toward zero’’.

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types; or— the left operand is a pointer to an object type and the right operand has integer type.
(Decrementing is equivalent to subtracting 1.)
Semantics
4

If both operands have arithmetic type, the usual arithmetic conversions are performed on
them.

5

The result of the binary + operator is the sum of the operands.

6

The result of the binary - operator is the difference resulting from the subtraction of thesecond operand from the first.

7

For the purposes of these operators, a pointer to an object that is not an element of anarray behaves the same as a pointer to the first element of an array of length one with thetype of the object as its element type.

8

When an expression that has integer type is added to or subtracted from a pointer, theresult has the type of the pointer operand. If the pointer operand points to an element ofan array object, and the array is large enough, the result points to an element offset fromthe original element such that the difference of the subscripts of the resulting and originalarray elements equals the integer expression. In other words, if the expression P points tothe i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and(P)-N (where N has the value n) point to, respectively, the i+n-th and i−n-th elements of
the array object, provided they exist. Moreover, if the expression P points to the lastelement of an array object, the expression (P)+1 points one past the last element of thearray object, and if the expression Q points one past the last element of an array object,
the expression (Q)-1 points to the last element of the array object. If both the pointeroperand and the result point to elements of the same array object, or one past the lastelement of the array object, the evaluation shall not produce an overflow; otherwise, thebehavior is undefined. If the result points one past the last element of the array object, it
shall not be used as the operand of a unary * operator that is evaluated.

9

When two pointers are subtracted, both shall point to elements of the same array object,
or one past the last element of the array object; the result is the difference of thesubscripts of the two array elements. The size of the result is implementation-defined,
and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header.
If the result is not representable in an object of that type, the behavior is undefined. In
other words, if the expressions P and Q point to, respectively, the i-th and j-th elements ofan array object, the expression (P)-(Q) has the value i−j provided the value fits in an
object of type ptrdiff_t. Moreover, if the expression P points either to an element ofan array object or one past the last element of an array object, and the expression Q points
to the last element of the same array object, the expression ((Q)+1)-(P) has the same
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value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if theexpression P points one past the last element of the array object, even though theexpression (Q)+1 does not point to an element of the array object.91)
10

EXAMPLE

Pointer arithmetic is well defined with pointers to variable length array types.

{
int n = 4, m = 3;
int a[n][m];int (*p)[m] = a; // p == &a[0]p += 1;// p == &a[1](*p)[2] = 99;// a[1][2] == 99
n = p - a;// n == 1}

11

If array a in the above example were declared to be an array of known constant size, and pointer p were
declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
the same.

Forward references: array declarators (6.7.5.2), common definitions <stddef.h>(7.17).

6.5.7 Bitwise shift operators
Syntax1

shift-expression:
additive-expression
shift-expression << additive-expression
shift-expression >> additive-expression
Constraints

2

Each of the operands shall have integer type.
Semantics

3

The integer promotions are performed on each of the operands. The type of the result isthat of the promoted left operand. If the value of the right operand is negative or isgreater than or equal to the width of the promoted left operand, the behavior is undefined.

91) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
this scheme the integer expression added to or subtracted from the converted pointer is first multipliedby the size of the object originally pointed to, and the resulting pointer is converted back to theoriginal type. For pointer subtraction, the result of the difference between the character pointers issimilarly divided by the size of the object originally pointed to.
When viewed in this way, an implementation need only provide one extra byte (which may overlap
another object in the program) just after the end of the object in order to satisfy the ‘‘one past the lastelement’’ requirements.

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4

The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled withzeros. If E1 has an unsigned type, the value of the result is E1 × 2E2 , reduced modulo
one more than the maximum value representable in the result type. If E1 has a signed
type and nonnegative value, and E1 × 2E2 is representable in the result type, then that is
the resulting value; otherwise, the behavior is undefined.

5

The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned typeor if E1 has a signed type and a nonnegative value, the value of the result is the integral
part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, theresulting value is implementation-defined.

6.5.8 Relational operators
Syntax1

relational-expression:
shift-expression
relational-expression < shift-expression
relational-expression > shift-expression
relational-expression <= shift-expression
relational-expression >= shift-expression
Constraints

2

One of the following shall hold:— both operands have real type;— both operands are pointers to qualified or unqualified versions of compatible object
types; or— both operands are pointers to qualified or unqualified versions of compatible
incomplete types.
Semantics

3

If both of the operands have arithmetic type, the usual arithmetic conversions are
performed.

4

For the purposes of these operators, a pointer to an object that is not an element of anarray behaves the same as a pointer to the first element of an array of length one with thetype of the object as its element type.

5

When two pointers are compared, the result depends on the relative locations in theaddress space of the objects pointed to. If two pointers to object or incomplete types both
point to the same object, or both point one past the last element of the same array object,they compare equal. If the objects pointed to are members of the same aggregate object,
pointers to structure members declared later compare greater than pointers to members
declared earlier in the structure, and pointers to array elements with larger subscript§6.5.8

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values compare greater than pointers to elements of the same array with lower subscript
values. All pointers to members of the same union object compare equal. If theexpression P points to an element of an array object and the expression Q points to thelast element of the same array object, the pointer expression Q+1 compares greater than
P. In all other cases, the behavior is undefined.
6

Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=(greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.92)
The result has type int.

6.5.9 Equality operators
Syntax1equality-expression:
relational-expression
equality-expression == relational-expression
equality-expression != relational-expression
Constraints

2

One of the following shall hold:— both operands have arithmetic type;— both operands are pointers to qualified or unqualified versions of compatible types;— one operand is a pointer to an object or incomplete type and the other is a pointer to aqualified or unqualified version of void; or— one operand is a pointer and the other is a null pointer constant.
Semantics

3

The == (equal to) and != (not equal to) operators are analogous to the relational
operators except for their lower precedence.93) Each of the operators yields 1 if thespecified relation is true and 0 if it is false. The result has type int. For any pair ofoperands, exactly one of the relations is true.

4

If both of the operands have arithmetic type, the usual arithmetic conversions are
performed. Values of complex types are equal if and only if both their real parts are equaland also their imaginary parts are equal. Any two values of arithmetic types fromdifferent type domains are equal if and only if the results of their conversions to the(complex) result type determined by the usual arithmetic conversions are equal.

92) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, itmeans (a<b)<c; in other words, ‘‘if a is less than b, compare 1 to c; otherwise, compare 0 to c’’.
93) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.

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5

Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is anull pointer constant, the null pointer constant is converted to the type of the pointer. If
one operand is a pointer to an object or incomplete type and the other is a pointer to aqualified or unqualified version of void, the former is converted to the type of the latter.

6

Two pointers compare equal if and only if both are null pointers, both are pointers to thesame object (including a pointer to an object and a subobject at its beginning) or function,
both are pointers to one past the last element of the same array object, or one is a pointerto one past the end of one array object and the other is a pointer to the start of a different
array object that happens to immediately follow the first array object in the address
space.94)

7

For the purposes of these operators, a pointer to an object that is not an element of anarray behaves the same as a pointer to the first element of an array of length one with thetype of the object as its element type.

6.5.10 Bitwise AND operator
Syntax1AND-expression:equality-expression
AND-expression & equality-expression
Constraints

2

Each of the operands shall have integer type.
Semantics

3

The usual arithmetic conversions are performed on the operands.

4

The result of the binary & operator is the bitwise AND of the operands (that is, each bit in
the result is set if and only if each of the corresponding bits in the converted operands isset).

94) Two objects may be adjacent in memory because they are adjacent elements of a larger array or
adjacent members of a structure with no padding between them, or because the implementation choseto place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses
outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined
behavior.

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6.5.11 Bitwise exclusive OR operator
Syntax1

exclusive-OR-expression:AND-expression
exclusive-OR-expression ^ AND-expression
Constraints

2

Each of the operands shall have integer type.
Semantics

3

The usual arithmetic conversions are performed on the operands.

4

The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit
in the result is set if and only if exactly one of the corresponding bits in the converted
operands is set).

6.5.12 Bitwise inclusive OR operator
Syntax1

inclusive-OR-expression:
exclusive-OR-expression
inclusive-OR-expression | exclusive-OR-expression
Constraints

2

Each of the operands shall have integer type.
Semantics

3

The usual arithmetic conversions are performed on the operands.

4

The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in
the result is set if and only if at least one of the corresponding bits in the converted
operands is set).

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6.5.13 Logical AND operator
Syntax1

logical-AND-expression:
inclusive-OR-expression
logical-AND-expression && inclusive-OR-expression
Constraints

2

Each of the operands shall have scalar type.
Semantics

3

The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, ityields 0. The result has type int.

4

Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation;
there is a sequence point after the evaluation of the first operand. If the first operandcompares equal to 0, the second operand is not evaluated.

6.5.14 Logical OR operator
Syntax1

logical-OR-expression:
logical-AND-expression
logical-OR-expression || logical-AND-expression
Constraints

2

Each of the operands shall have scalar type.
Semantics

3

The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, ityields 0. The result has type int.

4

Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; there isa sequence point after the evaluation of the first operand. If the first operand comparesunequal to 0, the second operand is not evaluated.

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6.5.15 Conditional operator
Syntax1

conditional-expression:
logical-OR-expression
logical-OR-expression ? expression : conditional-expression
Constraints

2

The first operand shall have scalar type.

3

One of the following shall hold for the second and third operands:— both operands have arithmetic type;— both operands have the same structure or union type;— both operands have void type;— both operands are pointers to qualified or unqualified versions of compatible types;— one operand is a pointer and the other is a null pointer constant; or— one operand is a pointer to an object or incomplete type and the other is a pointer to aqualified or unqualified version of void.
Semantics

4

The first operand is evaluated; there is a sequence point after its evaluation. The second
operand is evaluated only if the first compares unequal to 0; the third operand is evaluatedonly if the first compares equal to 0; the result is the value of the second or third operand(whichever is evaluated), converted to the type described below.95) If an attempt is madeto modify the result of a conditional operator or to access it after the next sequence point,
the behavior is undefined.

5

If both the second and third operands have arithmetic type, the result type that would bedetermined by the usual arithmetic conversions, were they applied to those two operands,is the type of the result. If both the operands have structure or union type, the result hasthat type. If both operands have void type, the result has void type.

6

If both the second and third operands are pointers or one is a null pointer constant and theother is a pointer, the result type is a pointer to a type qualified with all the type qualifiersof the types pointed-to by both operands. Furthermore, if both operands are pointers tocompatible types or to differently qualified versions of compatible types, the result type isa pointer to an appropriately qualified version of the composite type; if one operand is anull pointer constant, the result has the type of the other operand; otherwise, one operandis a pointer to void or a qualified version of void, in which case the result type is a95) A conditional expression does not yield an lvalue.

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pointer to an appropriately qualified version of void.
7

EXAMPLE The common type that results when the second and third operands are pointers is determinedin two independent stages. The appropriate qualifiers, for example, do not depend on whether the twopointers have compatible types.

8

Given the declarations
const void *c_vp;
void *vp;
const int *c_ip;
volatile int *v_ip;
int *ip;
const char *c_cp;
the third column in the following table is the common type that is the result of a conditional expression inwhich the first two columns are the second and third operands (in either order):
c_vp
v_ip
c_ip
vp
ip
vp

c_ip
0
v_ip
c_cp
c_ip
ip

const void *volatile int *const volatile int *const void *const int *void *

6.5.16 Assignment operators
Syntax1

assignment-expression:
conditional-expression
unary-expression assignment-operator assignment-expression
assignment-operator: one of= *= /= %= +=

-=

<<=

>>=

&=

^=

|=

Constraints
2

An assignment operator shall have a modifiable lvalue as its left operand.
Semantics

3

An assignment operator stores a value in the object designated by the left operand. An
assignment expression has the value of the left operand after the assignment, but is not anlvalue. The type of an assignment expression is the type of the left operand unless theleft operand has qualified type, in which case it is the unqualified version of the type ofthe left operand. The side effect of updating the stored value of the left operand shalloccur between the previous and the next sequence point.

4

The order of evaluation of the operands is unspecified. If an attempt is made to modify
the result of an assignment operator or to access it after the next sequence point, thebehavior is undefined.

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6.5.16.1 Simple assignment
Constraints
1

One of the following shall hold:96)— the left operand has qualified or unqualified arithmetic type and the right hasarithmetic type;— the left operand has a qualified or unqualified version of a structure or union typecompatible with the type of the right;— both operands are pointers to qualified or unqualified versions of compatible types,
and the type pointed to by the left has all the qualifiers of the type pointed to by theright;— one operand is a pointer to an object or incomplete type and the other is a pointer to aqualified or unqualified version of void, and the type pointed to by the left has all
the qualifiers of the type pointed to by the right;— the left operand is a pointer and the right is a null pointer constant; or— the left operand has type _Bool and the right is a pointer.
Semantics

2

In simple assignment (=), the value of the right operand is converted to the type of theassignment expression and replaces the value stored in the object designated by the left
operand.

3

If the value being stored in an object is read from another object that overlaps in any way
the storage of the first object, then the overlap shall be exact and the two objects shallhave qualified or unqualified versions of a compatible type; otherwise, the behavior isundefined.

4

EXAMPLE 1

In the program fragment

int f(void);char c;/* ... */if ((c = f()) == -1)/* ... */the int value returned by the function may be truncated when stored in the char, and then converted backto int width prior to the comparison. In an implementation in which ‘‘plain’’ char has the same range ofvalues as unsigned char (and char is narrower than int), the result of the conversion cannot be96) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion(specified in 6.3.2.1) that changes lvalues to ‘‘the value of the expression’’ and thus removes any type
qualifiers that were applied to the type category of the expression (for example, it removes const but
not volatile from the type int volatile * const).

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negative, so the operands of the comparison can never compare equal. Therefore, for full portability, thevariable c should be declared as int.

5

EXAMPLE 2

In the fragment:char c;int i;
long l;l = (c = i);the value of i is converted to the type of the assignment expression c = i, that is, char type. The valueof the expression enclosed in parentheses is then converted to the type of the outer assignment expression,that is, long int type.

6

EXAMPLE 3

Consider the fragment:

const char **cpp;
char *p;const char c = 'A';
cpp = &p;
*cpp = &c;*p = 0;// constraint violation// valid// valid

The first assignment is unsafe because it would allow the following valid code to attempt to change thevalue of the const object c.

6.5.16.2 Compound assignment
Constraints
1

For the operators += and -= only, either the left operand shall be a pointer to an object
type and the right shall have integer type, or the left operand shall have qualified or
unqualified arithmetic type and the right shall have arithmetic type.

2

For the other operators, each operand shall have arithmetic type consistent with thoseallowed by the corresponding binary operator.
Semantics

3

A compound assignment of the form E1 op = E2 differs from the simple assignment
expression E1 = E1 op (E2) only in that the lvalue E1 is evaluated only once.

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6.5.17 Comma operator
Syntax1

expression:
assignment-expression
expression , assignment-expression
Semantics

2

The left operand of a comma operator is evaluated as a void expression; there is asequence point after its evaluation. Then the right operand is evaluated; the result has its
type and value.97) If an attempt is made to modify the result of a comma operator or toaccess it after the next sequence point, the behavior is undefined.

3

EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
of initializers). On the other hand, it can be used within a parenthesized expression or within the second
expression of a conditional operator in such contexts. In the function callf(a, (t=3, t+2), c)
the function has three arguments, the second of which has the value 5.

Forward references: initialization (6.7.8).

97) A comma operator does not yield an lvalue.

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6.6 Constant expressions
Syntax1

constant-expression:
conditional-expression
Description

2

A constant expression can be evaluated during translation rather than runtime, andaccordingly may be used in any place that a constant may be.
Constraints

3

Constant expressions shall not contain assignment, increment, decrement, function-call,or comma operators, except when they are contained within a subexpression that is notevaluated.98)

4Each constant expression shall evaluate to a constant that is in the range of representablevalues for its type.
Semantics

5

An expression that evaluates to a constant is required in several contexts. If a floating
expression is evaluated in the translation environment, the arithmetic precision and range
shall be at least as great as if the expression were being evaluated in the execution
environment.

6

An integer constant expression99) shall have integer type and shall only have operands
that are integer constants, enumeration constants, character constants, sizeof
expressions whose results are integer constants, and floating constants that are theimmediate operands of casts. Cast operators in an integer constant expression shall only
convert arithmetic types to integer types, except as part of an operand to the sizeof
operator.

7

More latitude is permitted for constant expressions in initializers. Such a constant
expression shall be, or evaluate to, one of the following:— an arithmetic constant expression,— a null pointer constant,98) The operand of a sizeof operator is usually not evaluated (6.5.3.4).
99) An integer constant expression is used to specify the size of a bit-field member of a structure, thevalue of an enumeration constant, the size of an array, or the value of a case constant. Further
constraints that apply to the integer constant expressions used in conditional-inclusion preprocessing
directives are discussed in 6.10.1.

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WG14/N1256— an address constant, or— an address constant for an object type plus or minus an integer constant expression.
8

An arithmetic constant expression shall have arithmetic type and shall only haveoperands that are integer constants, floating constants, enumeration constants, character
constants, and sizeof expressions. Cast operators in an arithmetic constant expression
shall only convert arithmetic types to arithmetic types, except as part of an operand to asizeof operator whose result is an integer constant.

9

An address constant is a null pointer, a pointer to an lvalue designating an object of static
storage duration, or a pointer to a function designator; it shall be created explicitly using
the unary & operator or an integer constant cast to pointer type, or implicitly by the use ofan expression of array or function type. The array-subscript [] and member-access .
and -> operators, the address & and indirection * unary operators, and pointer casts may
be used in the creation of an address constant, but the value of an object shall not be
accessed by use of these operators.

10

An implementation may accept other forms of constant expressions.

11

The semantic rules for the evaluation of a constant expression are the same as fornonconstant expressions.100)
Forward references: array declarators (6.7.5.2), initialization (6.7.8).

100) Thus, in the following initialization,
static int i = 2 || 1 / 0;
the expression is a valid integer constant expression with value one.

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6.7 Declarations
Syntax1

declaration:
declaration-specifiers init-declarator-listopt ;declaration-specifiers:
storage-class-specifier declaration-specifiersopt
type-specifier declaration-specifiersopt
type-qualifier declaration-specifiersopt
function-specifier declaration-specifiersopt
init-declarator-list:
init-declarator
init-declarator-list , init-declarator
init-declarator:
declarator
declarator = initializer
Constraints

2

A declaration shall declare at least a declarator (other than the parameters of a function or
the members of a structure or union), a tag, or the members of an enumeration.

3

If an identifier has no linkage, there shall be no more than one declaration of the identifier(in a declarator or type specifier) with the same scope and in the same name space, except
for tags as specified in 6.7.2.3.

4

All declarations in the same scope that refer to the same object or function shall specify
compatible types.
Semantics

5

A declaration specifies the interpretation and attributes of a set of identifiers. A definitionof an identifier is a declaration for that identifier that:— for an object, causes storage to be reserved for that object;— for a function, includes the function body;101)— for an enumeration constant or typedef name, is the (only) declaration of theidentifier.

6

The declaration specifiers consist of a sequence of specifiers that indicate the linkage,storage duration, and part of the type of the entities that the declarators denote. The initdeclarator-list is a comma-separated sequence of declarators, each of which may have101) Function definitions have a different syntax, described in 6.9.1.

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additional type information, or an initializer, or both. The declarators contain theidentifiers (if any) being declared.
7

If an identifier for an object is declared with no linkage, the type for the object shall becomplete by the end of its declarator, or by the end of its init-declarator if it has an
initializer; in the case of function parameters (including in prototypes), it is the adjusted
type (see 6.7.5.3) that is required to be complete.

Forward references: declarators (6.7.5), enumeration specifiers (6.7.2.2), initialization(6.7.8).

6.7.1 Storage-class specifiers
Syntax1

storage-class-specifier:typedef
externstaticauto
registerConstraints

2

At most, one storage-class specifier may be given in the declaration specifiers in a
declaration.102)
Semantics

3

The typedef specifier is called a ‘‘storage-class specifier’’ for syntactic convenience
only; it is discussed in 6.7.7. The meanings of the various linkages and storage durations
were discussed in 6.2.2 and 6.2.4.

4

A declaration of an identifier for an object with storage-class specifier registersuggests that access to the object be as fast as possible. The extent to which suchsuggestions are effective is implementation-defined.103)

5The declaration of an identifier for a function that has block scope shall have no explicit
storage-class specifier other than extern.

102) See ‘‘future language directions’’ (6.11.5).
103) The implementation may treat any register declaration simply as an auto declaration. However,whether or not addressable storage is actually used, the address of any part of an object declared withstorage-class specifier register cannot be computed, either explicitly (by use of the unary &operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier
register is sizeof.

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6

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If an aggregate or union object is declared with a storage-class specifier other than
typedef, the properties resulting from the storage-class specifier, except with respect tolinkage, also apply to the members of the object, and so on recursively for any aggregate
or union member objects.
Forward references: type definitions (6.7.7).

6.7.2 Type specifiers
Syntax1

type-specifier:
void
char
short
int
long
float
doublesignedunsigned_Bool_Complex
struct-or-union-specifierenum-specifier
typedef-name∗Constraints
2

At least one type specifier shall be given in the declaration specifiers in each declaration,and in the specifier-qualifier list in each struct declaration and type name. Each list of
type specifiers shall be one of the following sets (delimited by commas, when there ismore than one set on a line); the type specifiers may occur in any order, possiblyintermixed with the other declaration specifiers.
— void— char— signed char
— unsigned char— short, signed short, short int, or signed short int— unsigned short, or unsigned short int— int, signed, or signed int§6.7.2

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WG14/N1256— unsigned, or unsigned int— long, signed long, long int, or signed long int— unsigned long, or unsigned long int— long long, signed long long, long long int, or
signed long long int— unsigned long long, or unsigned long long int— float— double— long double— _Bool— float _Complex— double _Complex— long double _Complex∗— struct or union specifier— enum specifier— typedef name3

The type specifier _Complex shall not be used if the implementation does not provide
complex types.104)

Semantics
4

Specifiers for structures, unions, and enumerations are discussed in 6.7.2.1 through6.7.2.3. Declarations of typedef names are discussed in 6.7.7. The characteristics of theother types are discussed in 6.2.5.

5Each of the comma-separated sets designates the same type, except that for bit-fields, it is
implementation-defined whether the specifier int designates the same type as signed
int or the same type as unsigned int.
Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers(6.7.2.1), tags (6.7.2.3), type definitions (6.7.7).

∗

104) Freestanding implementations are not required to provide complex types.

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6.7.2.1 Structure and union specifiers
Syntax1

struct-or-union-specifier:struct-or-union identifieropt { struct-declaration-list }struct-or-union identifier
struct-or-union:
structunion
struct-declaration-list:
struct-declaration
struct-declaration-list struct-declaration
struct-declaration:
specifier-qualifier-list struct-declarator-list ;specifier-qualifier-list:
type-specifier specifier-qualifier-listopt
type-qualifier specifier-qualifier-listopt
struct-declarator-list:
struct-declarator
struct-declarator-list , struct-declarator
struct-declarator:
declarator
declaratoropt : constant-expression
Constraints

2

A structure or union shall not contain a member with incomplete or function type (hence,a structure shall not contain an instance of itself, but may contain a pointer to an instanceof itself), except that the last member of a structure with more than one named member
may have incomplete array type; such a structure (and any union containing, possibly
recursively, a member that is such a structure) shall not be a member of a structure or anelement of an array.

3

The expression that specifies the width of a bit-field shall be an integer constant
expression with a nonnegative value that does not exceed the width of an object of thetype that would be specified were the colon and expression omitted. If the value is zero,the declaration shall have no declarator.

4

A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
int, unsigned int, or some other implementation-defined type.

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Semantics
5

As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
storage is allocated in an ordered sequence, and a union is a type consisting of a sequenceof members whose storage overlap.

6Structure and union specifiers have the same form. The keywords struct and union
indicate that the type being specified is, respectively, a structure type or a union type.

7

The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,within a translation unit. The struct-declaration-list is a sequence of declarations for themembers of the structure or union. If the struct-declaration-list contains no named
members, the behavior is undefined. The type is incomplete until after the } thatterminates the list.

8

A member of a structure or union may have any object type other than a variably
modified type.105) In addition, a member may be declared to consist of a specified
number of bits (including a sign bit, if any). Such a member is called a bit-field;106) its
width is preceded by a colon.

9

A bit-field is interpreted as a signed or unsigned integer type consisting of the specified
number of bits.107) If the value 0 or 1 is stored into a nonzero-width bit-field of type
_Bool, the value of the bit-field shall compare equal to the value stored.

10

An implementation may allocate any addressable storage unit large enough to hold a bitfield. If enough space remains, a bit-field that immediately follows another bit-field in a
structure shall be packed into adjacent bits of the same unit. If insufficient space remains,whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
implementation-defined. The order of allocation of bit-fields within a unit (high-order tolow-order or low-order to high-order) is implementation-defined. The alignment of theaddressable storage unit is unspecified.

11

A bit-field declaration with no declarator, but only a colon and a width, indicates anunnamed bit-field.108) As a special case, a bit-field structure member with a width of 0
indicates that no further bit-field is to be packed into the unit in which the previous bitfield, if any, was placed.
105) A structure or union can not contain a member with a variably modified type because member names
are not ordinary identifiers as defined in 6.2.3.
106) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers toor arrays of bit-field objects.
107) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
then it is implementation-defined whether the bit-field is signed or unsigned.
108) An unnamed bit-field structure member is useful for padding to conform to externally imposedlayouts.

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12Each non-bit-field member of a structure or union object is aligned in an implementationdefined manner appropriate to its type.

13

Within a structure object, the non-bit-field members and the units in which bit-fields
reside have addresses that increase in the order in which they are declared. A pointer to a
structure object, suitably converted, points to its initial member (or if that member is a
bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
padding within a structure object, but not at its beginning.

14

The size of a union is sufficient to contain the largest of its members. The value of at
most one of the members can be stored in a union object at any time. A pointer to aunion object, suitably converted, points to each of its members (or if a member is a bitfield, then to the unit in which it resides), and vice versa.

15

There may be unnamed padding at the end of a structure or union.

16

As a special case, the last element of a structure with more than one named member may
have an incomplete array type; this is called a flexible array member. In most situations,the flexible array member is ignored. In particular, the size of the structure is as if theflexible array member were omitted except that it may have more trailing padding thanthe omission would imply. However, when a . (or ->) operator has a left operand that is(a pointer to) a structure with a flexible array member and the right operand names thatmember, it behaves as if that member were replaced with the longest array (with the sameelement type) that would not make the structure larger than the object being accessed; theoffset of the array shall remain that of the flexible array member, even if this would differ
from that of the replacement array. If this array would have no elements, it behaves as if
it had one element but the behavior is undefined if any attempt is made to access thatelement or to generate a pointer one past it.

17

EXAMPLE

After the declaration:

struct s { int n; double d[]; };the structure struct s has a flexible array member d. A typical way to use this is:

int m = /* some value */;struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
p had been declared as:

struct { int n; double d[m]; } *p;(there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
not be the same).

18

Following the above declaration:§6.7.2.1

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struct s t1 = { 0 };struct s t2 = { 1, { 4.2 }};t1.n = 4;
t1.d[0] = 4.2;

WG14/N1256// valid// invalid// valid// might be undefined behavior

The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did notcontain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible thatsizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
code.

19

After the further declaration:

struct ss { int n; };the expressions:sizeof (struct s) >= sizeof (struct ss)
sizeof (struct s) >= offsetof(struct s, d)

are always equal to 1.

20

If sizeof (double) is 8, then after the following code is executed:
struct s *s1;
struct s *s2;
s1 = malloc(sizeof (struct s) + 64);s2 = malloc(sizeof (struct s) + 46);
and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
purposes, as if the identifiers had been declared as:

struct { int n; double d[8]; } *s1;
struct { int n; double d[5]; } *s2;

21

Following the further successful assignments:
s1 = malloc(sizeof (struct s) + 10);s2 = malloc(sizeof (struct s) + 6);
they then behave as if the declarations were:struct { int n; double d[1]; } *s1, *s2;
and:double *dp;
dp = &(s1->d[0]); // valid*dp = 42;// valid
dp = &(s2->d[0]); // valid*dp = 42;// undefined behavior

22

The assignment:*s1 = *s2;
only copies the member n; if any of the array elements are within the first sizeof (struct s) bytesof the structure, they might be copied or simply overwritten with indeterminate values.

Forward references: tags (6.7.2.3).
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6.7.2.2 Enumeration specifiers
Syntax1

enum-specifier:enum identifieropt { enumerator-list }enum identifieropt { enumerator-list , }enum identifier
enumerator-list:
enumerator
enumerator-list , enumerator
enumerator:
enumeration-constantenumeration-constant = constant-expression
Constraints

2

The expression that defines the value of an enumeration constant shall be an integer
constant expression that has a value representable as an int.
Semantics

3

The identifiers in an enumerator list are declared as constants that have type int andmay appear wherever such are permitted.109) An enumerator with = defines its
enumeration constant as the value of the constant expression. If the first enumerator has
no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =defines its enumeration constant as the value of the constant expression obtained byadding 1 to the value of the previous enumeration constant. (The use of enumerators with= may produce enumeration constants with values that duplicate other values in the same
enumeration.) The enumerators of an enumeration are also known as its members.

4

Each enumerated type shall be compatible with char, a signed integer type, or an
unsigned integer type. The choice of type is implementation-defined,110) but shall becapable of representing the values of all the members of the enumeration. The
enumerated type is incomplete until after the } that terminates the list of enumerator
declarations.

109) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct fromeach other and from other identifiers declared in ordinary declarators.
110) An implementation may delay the choice of which integer type until all enumeration constants havebeen seen.

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The following fragment:

enum hue { chartreuse, burgundy, claret=20, winedark };enum hue col, *cp;
col = claret;
cp = &col;if (*cp != burgundy)/* ... */makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as apointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.

Forward references: tags (6.7.2.3).

6.7.2.3 Tags
Constraints
1

A specific type shall have its content defined at most once.

2

Where two declarations that use the same tag declare the same type, they shall both use
the same choice of struct, union, or enum.

3

A type specifier of the form
enum identifier
without an enumerator list shall only appear after the type it specifies is complete.
Semantics

4

All declarations of structure, union, or enumerated types that have the same scope anduse the same tag declare the same type. The type is incomplete111) until the closing braceof the list defining the content, and complete thereafter.

5

Two declarations of structure, union, or enumerated types which are in different scopes oruse different tags declare distinct types. Each declaration of a structure, union, or
enumerated type which does not include a tag declares a distinct type.

6

A type specifier of the form
struct-or-union identifieropt { struct-declaration-list }orenum identifier { enumerator-list }orenum identifier { enumerator-list , }declares a structure, union, or enumerated type. The list defines the structure content,
111) An incomplete type may only by used when the size of an object of that type is not needed. It is notneeded, for example, when a typedef name is declared to be a specifier for a structure or union, or
when a pointer to or a function returning a structure or union is being declared. (See incomplete types
in 6.2.5.) The specification has to be complete before such a function is called or defined.

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union content, or enumeration content. If an identifier is provided,112) the type specifier
also declares the identifier to be the tag of that type.
7

A declaration of the form
struct-or-union identifier ;specifies a structure or union type and declares the identifier as a tag of that type.113)

8

If a type specifier of the form
struct-or-union identifier
occurs other than as part of one of the above forms, and no other declaration of theidentifier as a tag is visible, then it declares an incomplete structure or union type, anddeclares the identifier as the tag of that type.113)

9

If a type specifier of the form
struct-or-union identifierorenum identifier
occurs other than as part of one of the above forms, and a declaration of the identifier as atag is visible, then it specifies the same type as that other declaration, and does notredeclare the tag.

10

EXAMPLE 1

This mechanism allows declaration of a self-referential structure.

struct tnode {int count;struct tnode *left, *right;};
specifies a structure that contains an integer and two pointers to objects of the same type. Once thisdeclaration has been given, the declaration
struct tnode s, *sp;declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
these declarations, the expression sp->left refers to the left struct tnode pointer of the object towhich sp points; the expression s.right->count designates the count member of the right structtnode pointed to from s.

11

The following alternative formulation uses the typedef mechanism:112) If there is no identifier, the type can, within the translation unit, only be referred to by the declarationof which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
can make use of that typedef name to declare objects having the specified structure, union, or
enumerated type.
113) A similar construction with enum does not exist.

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typedef struct tnode TNODE;
struct tnode {int count;
TNODE *left, *right;};
TNODE s, *sp;

12

EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
structures, the declarations
struct s1 { struct s2 *s2p; /* ... */ }; // D1
struct s2 { struct s1 *s1p; /* ... */ }; // D2
specify a pair of structures that contain pointers to each other. Note, however, that if s2 were alreadydeclared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
D2. To eliminate this context sensitivity, the declaration
struct s2;
may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 thencompletes the specification of the new type.

Forward references: declarators (6.7.5), array declarators (6.7.5.2), type definitions(6.7.7).

6.7.3 Type qualifiers
Syntax1

type-qualifier:
const
restrict
volatile
Constraints

2

Types other than pointer types derived from object or incomplete types shall not be
restrict-qualified.
Semantics

3

The properties associated with qualified types are meaningful only for expressions thatare lvalues.114)

4

If the same qualifier appears more than once in the same specifier-qualifier-list, either
directly or via one or more typedefs, the behavior is the same as if it appeared only
once.

114) The implementation may place a const object that is not volatile in a read-only region ofstorage. Moreover, the implementation need not allocate storage for such an object if its address isnever used.

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5

If an attempt is made to modify an object defined with a const-qualified type through useof an lvalue with non-const-qualified type, the behavior is undefined. If an attempt ismade to refer to an object defined with a volatile-qualified type through use of an lvalue
with non-volatile-qualified type, the behavior is undefined.115)

6

An object that has volatile-qualified type may be modified in ways unknown to theimplementation or have other unknown side effects. Therefore any expression referring
to such an object shall be evaluated strictly according to the rules of the abstract machine,
as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in theobject shall agree with that prescribed by the abstract machine, except as modified by the
unknown factors mentioned previously.116) What constitutes an access to an object thathas volatile-qualified type is implementation-defined.

7

An object that is accessed through a restrict-qualified pointer has a special association
with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses tothat object use, directly or indirectly, the value of that particular pointer.117) The intended
use of the restrict qualifier (like the register storage class) is to promote
optimization, and deleting all instances of the qualifier from all preprocessing translation
units composing a conforming program does not change its meaning (i.e., observablebehavior).

8

If the specification of an array type includes any type qualifiers, the element type is soqualified, not the array type. If the specification of a function type includes any type
qualifiers, the behavior is undefined.118)

9

For two qualified types to be compatible, both shall have the identically qualified version
of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
does not affect the specified type.

10

EXAMPLE 1

An object declared

extern const volatile int real_time_clock;may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.

115) This applies to those objects that behave as if they were defined with qualified types, even if they arenever actually defined as objects in the program (such as an object at a memory-mapped input/output
address).
116) A volatile declaration may be used to describe an object corresponding to a memory-mapped
input/output port or an object accessed by an asynchronously interrupting function. Actions on
objects so declared shall not be ‘‘optimized out’’ by an implementation or reordered except aspermitted by the rules for evaluating expressions.
117) For example, a statement that assigns a value returned by malloc to a single pointer establishes thisassociation between the allocated object and the pointer.
118) Both of these can occur through the use of typedefs.

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EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
modify an aggregate type:
const struct s { int mem; } cs = { 1 };struct s ncs; // the object ncs is modifiable
typedef int A[2][3];const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
int *pi;const int *pci;ncs = cs;// validcs = ncs;// violates modifiable lvalue constraint for =pi = &ncs.mem; // valid
pi = &cs.mem; // violates type constraints for =pci = &cs.mem; // valid
pi = a[0];// invalid: a[0] has type ‘‘const int *’’6.7.3.1 Formal definition of restrict
1

Let D be a declaration of an ordinary identifier that provides a means of designating an
object P as a restrict-qualified pointer to type T.

2

If D appears inside a block and does not have storage class extern, let B denote theblock. If D appears in the list of parameter declarations of a function definition, let B
denote the associated block. Otherwise, let B denote the block of main (or the block ofwhatever function is called at program startup in a freestanding environment).

3

In what follows, a pointer expression E is said to be based on object P if (at somesequence point in the execution of B prior to the evaluation of E) modifying P to point toa copy of the array object into which it formerly pointed would change the value of E.119)
Note that ‘‘based’’ is defined only for expressions with pointer types.

4

During each execution of B, let L be any lvalue that has &L based on P. If L is used toaccess the value of the object X that it designates, and X is also modified (by any means),
then the following requirements apply: T shall not be const-qualified. Every other lvalue
used to access the value of X shall also have its address based on P. Every access thatmodifies X shall be considered also to modify P, for the purposes of this subclause. If P
is assigned the value of a pointer expression E that is based on another restricted pointerobject P2, associated with block B2, then either the execution of B2 shall begin before
the execution of B, or the execution of B2 shall end prior to the assignment. If theserequirements are not met, then the behavior is undefined.

5

Here an execution of B means that portion of the execution of the program that would
correspond to the lifetime of an object with scalar type and automatic storage duration
119) In other words, E depends on the value of P itself rather than on the value of an object referenced
indirectly through P. For example, if identifier p has type (int **restrict), then the pointerexpressions p and p+1 are based on the restricted pointer object designated by p, but the pointerexpressions *p and p[1] are not.

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associated with B.
6

A translator is free to ignore any or all aliasing implications of uses of restrict.

7

EXAMPLE 1

The file scope declarations

int * restrict a;
int * restrict b;
extern int c[];assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
program, then it is never accessed using either of the other two.

8

EXAMPLE 2 The function parameter declarations in the following example
void f(int n, int * restrict p, int * restrict q){
while (n-- > 0)*p++ = *q++;}assert that, during each execution of the function, if an object is accessed through one of the pointerparameters, then it is not also accessed through the other.

9

The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
analysis of function f without examining any of the calls of f in the program. The cost is that the
programmer has to examine all of those calls to ensure that none give undefined behavior. For example, thesecond call of f in g has undefined behavior because each of d[1] through d[49] is accessed throughboth p and q.
void g(void){extern int d[100];f(50, d + 50, d); // validf(50, d + 1, d); // undefined behavior}

10

EXAMPLE 3

The function parameter declarations

void h(int n, int * restrict p, int * restrict q, int * restrict r){
int i;for (i = 0; i < n; i++)p[i] = q[i] + r[i];}illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
modified within function h.

11

EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between afunction call and an equivalent nested block. With one exception, only ‘‘outer-to-inner’’ assignments
between restricted pointers declared in nested blocks have defined behavior.

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int * restrict p1;
int * restrict q1;
p1 = q1; // undefined behavior{
int * restrict p2 = p1; // valid
int * restrict q2 = q1; // valid
p1 = q2;// undefined behavior
p2 = q2;// undefined behavior}}

12

The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
example, this permits new_vector to return a vector.
typedef struct { int n; float * restrict v; } vector;
vector new_vector(int n){vector t;
t.n = n;t.v = malloc(n * sizeof (float));return t;}

6.7.4 Function specifiers
Syntax1function-specifier:inlineConstraints

2

Function specifiers shall be used only in the declaration of an identifier for a function.

3

An inline definition of a function with external linkage shall not contain a definition of amodifiable object with static storage duration, and shall not contain a reference to an
identifier with internal linkage.

4

In a hosted environment, the inline function specifier shall not appear in a declarationof main.
Semantics

5

A function declared with an inline function specifier is an inline function. The
function specifier may appear more than once; the behavior is the same as if it appeared
only once. Making a function an inline function suggests that calls to the function be as
fast as possible.120) The extent to which such suggestions are effective is
implementation-defined.121)

6

Any function with internal linkage can be an inline function. For a function with external
linkage, the following restrictions apply: If a function is declared with an inline
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function specifier, then it shall also be defined in the same translation unit. If all of thefile scope declarations for a function in a translation unit include the inline function
specifier without extern, then the definition in that translation unit is an inline
definition. An inline definition does not provide an external definition for the function,and does not forbid an external definition in another translation unit. An inline definition
provides an alternative to an external definition, which a translator may use to implement
any call to the function in the same translation unit. It is unspecified whether a call to thefunction uses the inline definition or the external definition.122)
7

EXAMPLE The declaration of an inline function with external linkage can result in either an external
definition, or a definition available for use only within the translation unit. A file scope declaration withextern creates an external definition. The following example shows an entire translation unit.
inline double fahr(double t){return (9.0 * t) / 5.0 + 32.0;}
inline double cels(double t){return (5.0 * (t - 32.0)) / 9.0;}
extern double fahr(double);// creates an external definition

double convert(int is_fahr, double temp){/* A translator may perform inline substitutions */return is_fahr ? cels(temp) : fahr(temp);}

8Note that the definition of fahr is an external definition because fahr is also declared with extern, but
the definition of cels is an inline definition. Because cels has external linkage and is referenced, anexternal definition has to appear in another translation unit (see 6.9); the inline definition and the external
definition are distinct and either may be used for the call.

Forward references: function definitions (6.9.1).

120) By using, for example, an alternative to the usual function call mechanism, such as ‘‘inline
substitution’’. Inline substitution is not textual substitution, nor does it create a new function.
Therefore, for example, the expansion of a macro used within the body of the function uses thedefinition it had at the point the function body appears, and not where the function is called; andidentifiers refer to the declarations in scope where the body occurs. Likewise, the function has asingle address, regardless of the number of inline definitions that occur in addition to the external
definition.
121) For example, an implementation might never perform inline substitution, or might only perform inline
substitutions to calls in the scope of an inline declaration.
122) Since an inline definition is distinct from the corresponding external definition and from any othercorresponding inline definitions in other translation units, all corresponding objects with static storage
duration are also distinct in each of the definitions.

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6.7.5 Declarators
Syntax1

declarator:
pointeropt direct-declarator
direct-declarator:
identifier( declarator )direct-declarator [ type-qualifier-listopt assignment-expressionopt ]direct-declarator [ static type-qualifier-listopt assignment-expression ]direct-declarator [ type-qualifier-list static assignment-expression ]direct-declarator [ type-qualifier-listopt * ]direct-declarator ( parameter-type-list )direct-declarator ( identifier-listopt )pointer:* type-qualifier-listopt* type-qualifier-listopt pointertype-qualifier-list:
type-qualifier
type-qualifier-list type-qualifierparameter-type-list:
parameter-list
parameter-list , ...
parameter-list:
parameter-declaration
parameter-list , parameter-declaration
parameter-declaration:
declaration-specifiers declarator
declaration-specifiers abstract-declaratoropt
identifier-list:
identifier
identifier-list , identifier
Semantics

2

Each declarator declares one identifier, and asserts that when an operand of the same
form as the declarator appears in an expression, it designates a function or object with thescope, storage duration, and type indicated by the declaration specifiers.

3

A full declarator is a declarator that is not part of another declarator. The end of a fulldeclarator is a sequence point. If, in the nested sequence of declarators in a full
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declarator, there is a declarator specifying a variable length array type, the type specified
by the full declarator is said to be variably modified. Furthermore, any type derived bydeclarator type derivation from a variably modified type is itself variably modified.

4

In the following subclauses, consider a declaration
T D1
where T contains the declaration specifiers that specify a type T (such as int) and D1 isa declarator that contains an identifier ident. The type specified for the identifier ident in
the various forms of declarator is described inductively using this notation.

5

If, in the declaration ‘‘T D1’’, D1 has the form
identifier
then the type specified for ident is T .

6

If, in the declaration ‘‘T D1’’, D1 has the form
( D )then ident has the type specified by the declaration ‘‘T D’’. Thus, a declarator inparentheses is identical to the unparenthesized declarator, but the binding of complicateddeclarators may be altered by parentheses.
Implementation limits

7

As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, andfunction declarators that modify an arithmetic, structure, union, or incomplete type, either
directly or via one or more typedefs.
Forward references: array declarators (6.7.5.2), type definitions (6.7.7).

6.7.5.1 Pointer declarators
Semantics
1

If, in the declaration ‘‘T D1’’, D1 has the form
* type-qualifier-listopt D
and the type specified for ident in the declaration ‘‘T D’’ is ‘‘derived-declarator-type-list
T ’’, then the type specified for ident is ‘‘derived-declarator-type-list type-qualifier-list
pointer to T ’’. For each type qualifier in the list, ident is a so-qualified pointer.

2

For two pointer types to be compatible, both shall be identically qualified and both shallbe pointers to compatible types.

3

EXAMPLE The following pair of declarations demonstrates the difference between a ‘‘variable pointerto a constant value’’ and a ‘‘constant pointer to a variable value’’.

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const int *ptr_to_constant;int *const constant_ptr;
The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of theint pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to thesame location.

4

The declaration of the constant pointer constant_ptr may be clarified by including a definition for thetype ‘‘pointer to int’’.
typedef int *int_ptr;
const int_ptr constant_ptr;
declares constant_ptr as an object that has type ‘‘const-qualified pointer to int’’.

6.7.5.2 Array declarators
Constraints
1

In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
an expression or *. If they delimit an expression (which specifies the size of an array), theexpression shall have an integer type. If the expression is a constant expression, it shallhave a value greater than zero. The element type shall not be an incomplete or function
type. The optional type qualifiers and the keyword static shall appear only in a
declaration of a function parameter with an array type, and then only in the outermost
array type derivation.

2

An ordinary identifier (as defined in 6.2.3) that has a variably modified type shall have
either block scope and no linkage or function prototype scope. If an identifier is declared
to be an object with static storage duration, it shall not have a variable length array type.

Semantics
3

If, in the declaration ‘‘T D1’’, D1 has one of the forms:
D[ type-qualifier-listopt assignment-expressionopt ]D[ static type-qualifier-listopt assignment-expression ]D[ type-qualifier-list static assignment-expression ]D[ type-qualifier-listopt * ]and the type specified for ident in the declaration ‘‘T D’’ is ‘‘derived-declarator-type-list
T ’’, then the type specified for ident is ‘‘derived-declarator-type-list array of T ’’.123)(See 6.7.5.3 for the meaning of the optional type qualifiers and the keyword static.)

4

If the size is not present, the array type is an incomplete type. If the size is * instead ofbeing an expression, the array type is a variable length array type of unspecified size,
which can only be used in declarations with function prototype scope;124) such arrays arenonetheless complete types. If the size is an integer constant expression and the element123) When several ‘‘array of’’ specifications are adjacent, a multidimensional array is declared.

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type has a known constant size, the array type is not a variable length array type;otherwise, the array type is a variable length array type.
5

If the size is an expression that is not an integer constant expression: if it occurs in a
declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
each time it is evaluated it shall have a value greater than zero. The size of each instanceof a variable length array type does not change during its lifetime. Where a size
expression is part of the operand of a sizeof operator and changing the value of thesize expression would not affect the result of the operator, it is unspecified whether or not
the size expression is evaluated.

6

For two array types to be compatible, both shall have compatible element types, and if
both size specifiers are present, and are integer constant expressions, then both size
specifiers shall have the same constant value. If the two array types are used in a context
which requires them to be compatible, it is undefined behavior if the two size specifiers
evaluate to unequal values.

7

EXAMPLE 1
float fa[11], *afp[17];declares an array of float numbers and an array of pointers to float numbers.

8

EXAMPLE 2

Note the distinction between the declarations

extern int *x;
extern int y[];The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
(an incomplete type), the storage for which is defined elsewhere.

9

EXAMPLE 3

The following declarations demonstrate the compatibility rules for variably modified types.

extern int n;extern int m;void fcompat(void){
int a[n][6][m];int (*p)[4][n+1];
int c[n][n][6][m];int (*r)[n][n][n+1];
p = a;// invalid: not compatible because 4 != 6r = c;// compatible, but defined behavior only if// n == 6 and m == n+1}

124) Thus, * can be used only in function declarations that are not definitions (see 6.7.5.3).

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EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope orfunction prototype scope. Array objects declared with the static or extern storage-class specifier
cannot have a variable length array (VLA) type. However, an object declared with the static storageclass specifier can have a VM type (that is, a pointer to a VLA type). Finally, all identifiers declared with a
VM type have to be ordinary identifiers and cannot, therefore, be members of structures or unions.
extern int n;
int A[n];extern int (*p2)[n];int B[100];// invalid: file scope VLA// invalid: file scope VM// valid: file scope but not VM

void fvla(int m, int C[m][m]);// valid: VLA with prototype scope

void fvla(int m, int C[m][m]){typedef int VLA[m][m];// valid: adjusted to auto pointer to VLA

struct tag {int (*y)[n];int z[n];};int D[m];static int E[m];extern int F[m];int (*s)[m];extern int (*r)[m];static int (*q)[m] = &B;// valid: block scope typedef VLA// invalid: y not ordinary identifier// invalid: z not ordinary identifier// valid: auto VLA// invalid: static block scope VLA// invalid: F has linkage and is VLA// valid: auto pointer to VLA// invalid: r has linkage and points to VLA// valid: q is a static block pointer to VLA}

Forward references:initialization (6.7.8).

function declarators (6.7.5.3), function definitions (6.9.1),

6.7.5.3 Function declarators (including prototypes)
Constraints
1

A function declarator shall not specify a return type that is a function type or an array
type.

2

The only storage-class specifier that shall occur in a parameter declaration is register.

3

An identifier list in a function declarator that is not part of a definition of that function
shall be empty.

4

After adjustment, the parameters in a parameter type list in a function declarator that ispart of a definition of that function shall not have incomplete type.
Semantics

5

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and the type specified for ident in the declaration ‘‘T D’’ is ‘‘derived-declarator-type-list
T ’’, then the type specified for ident is ‘‘derived-declarator-type-list function returning
T ’’.
6

A parameter type list specifies the types of, and may declare identifiers for, theparameters of the function.

7

A declaration of a parameter as ‘‘array of type’’ shall be adjusted to ‘‘qualified pointer totype’’, where the type qualifiers (if any) are those specified within the [ and ] of thearray type derivation. If the keyword static also appears within the [ and ] of thearray type derivation, then for each call to the function, the value of the corresponding
actual argument shall provide access to the first element of an array with at least as many
elements as specified by the size expression.

8

A declaration of a parameter as ‘‘function returning type’’ shall be adjusted to ‘‘pointer tofunction returning type’’, as in 6.3.2.1.

9

If the list terminates with an ellipsis (, ...), no information about the number or typesof the parameters after the comma is supplied.125)

10The special case of an unnamed parameter of type void as the only item in the list
specifies that the function has no parameters.

11

If, in a parameter declaration, an identifier can be treated either as a typedef name or as aparameter name, it shall be taken as a typedef name.

12

If the function declarator is not part of a definition of that function, parameters may haveincomplete type and may use the [*] notation in their sequences of declarator specifiersto specify variable length array types.

13

The storage-class specifier in the declaration specifiers for a parameter declaration, if
present, is ignored unless the declared parameter is one of the members of the parameter
type list for a function definition.

14

An identifier list declares only the identifiers of the parameters of the function. An empty
list in a function declarator that is part of a definition of that function specifies that thefunction has no parameters. The empty list in a function declarator that is not part of adefinition of that function specifies that no information about the number or types of theparameters is supplied.126)

15

For two function types to be compatible, both shall specify compatible return types.127)

125) The macros defined in the <stdarg.h> header (7.15) may be used to access arguments that
correspond to the ellipsis.
126) See ‘‘future language directions’’ (6.11.6).
127) If both function types are ‘‘old style’’, parameter types are not compared.

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Moreover, the parameter type lists, if both are present, shall agree in the number ofparameters and in use of the ellipsis terminator; corresponding parameters shall havecompatible types. If one type has a parameter type list and the other type is specified by afunction declarator that is not part of a function definition and that contains an empty
identifier list, the parameter list shall not have an ellipsis terminator and the type of eachparameter shall be compatible with the type that results from the application of thedefault argument promotions. If one type has a parameter type list and the other type is
specified by a function definition that contains a (possibly empty) identifier list, both shallagree in the number of parameters, and the type of each prototype parameter shall becompatible with the type that results from the application of the default argument
promotions to the type of the corresponding identifier. (In the determination of typecompatibility and of a composite type, each parameter declared with function or array
type is taken as having the adjusted type and each parameter declared with qualified type
is taken as having the unqualified version of its declared type.)
16

EXAMPLE 1

The declaration

int f(void), *fip(), (*pfi)();declares a function f with no parameters returning an int, a function fip with no parameter specification
returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that thedeclaration suggests, and the same construction in an expression requires, the calling of a function fip,and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), theextra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
designator, which is then used to call the function; it returns an int.

17

If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If thedeclaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
internal or external linkage (depending on what file scope declarations for these identifiers are visible), andthe identifier of the pointer pfi has block scope and no linkage.

18

EXAMPLE 2

The declaration

int (*apfi[3])(int *x, int *y);declares an array apfi of three pointers to functions returning int. Each of these functions has two
parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only andgo out of scope at the end of the declaration of apfi.

19

EXAMPLE 3

The declaration

int (*fpfi(int (*)(long), int))(int, ...);
declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
additional arguments of any type.

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The following prototype has a variably modified parameter.

void addscalar(int n, int m,
double a[n][n*m+300], double x);
int main(){double b[4][308];
addscalar(4, 2, b, 2.17);
return 0;}
void addscalar(int n, int m,
double a[n][n*m+300], double x){
for (int i = 0; i < n; i++)for (int j = 0, k = n*m+300; j < k; j++)// a is a pointer to a VLA with n*m+300 elementsa[i][j] += x;}

21

EXAMPLE 5

The following are all compatible function prototype declarators.

double maximum(int n, int m, double a[n][m]);double maximum(int n, int m, double a[*][*]);
double maximum(int n, int m, double a[ ][*]);
double maximum(int n, int m, double a[ ][m]);as are:void f(double (* restrict a)[5]);void f(double a[restrict][5]);void f(double a[restrict 3][5]);void f(double a[restrict static 3][5]);(Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)Forward references: function definitions (6.9.1), type names (6.7.6).

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6.7.6 Type names
Syntax1

type-name:specifier-qualifier-list abstract-declaratoropt
abstract-declarator:
pointerpointeropt direct-abstract-declarator
direct-abstract-declarator:( abstract-declarator )direct-abstract-declaratoropt [ type-qualifier-listopt
assignment-expressionopt ]direct-abstract-declaratoropt [ static type-qualifier-listopt
assignment-expression ]direct-abstract-declaratoropt [ type-qualifier-list static
assignment-expression ]direct-abstract-declaratoropt [ * ]direct-abstract-declaratoropt ( parameter-type-listopt )Semantics
2

In several contexts, it is necessary to specify a type. This is accomplished using a typename, which is syntactically a declaration for a function or an object of that type thatomits the identifier.128)

3

EXAMPLE
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)

The constructions
int
int *
int *[3]int (*)[3]int (*)[*]
int *()
int (*)(void)
int (*const [])(unsigned int, ...)

name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to anarray of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
parameter that has type unsigned int and an unspecified number of other parameters, returning anint.

128) As indicated by the syntax, empty parentheses in a type name are interpreted as ‘‘function with noparameter specification’’, rather than redundant parentheses around the omitted identifier.

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6.7.7 Type definitions
Syntax1

typedef-name:identifier
Constraints

2

If a typedef name specifies a variably modified type then it shall have block scope.
Semantics

3

In a declaration whose storage-class specifier is typedef, each declarator defines anidentifier to be a typedef name that denotes the type specified for the identifier in the way
described in 6.7.5. Any array size expressions associated with variable length arraydeclarators are evaluated each time the declaration of the typedef name is reached in theorder of execution. A typedef declaration does not introduce a new type, only asynonym for the type so specified. That is, in the following declarations:typedef T type_ident;
type_ident D;
type_ident is defined as a typedef name with the type specified by the declaration
specifiers in T (known as T ), and the identifier in D has the type ‘‘derived-declaratortype-list T ’’ where the derived-declarator-type-list is specified by the declarators of D. A
typedef name shares the same name space as other identifiers declared in ordinary
declarators.

4

EXAMPLE 1

After

typedef int MILES, KLICKSP();
typedef struct { double hi, lo; } range;
the constructions
MILES distance;
extern KLICKSP *metricp;
range x;range z, *zp;
are all valid declarations. The type of distance is int, that of metricp is ‘‘pointer to function with noparameter specification returning int’’, and that of x and z is the specified structure; zp is a pointer tosuch a structure. The object distance has a type compatible with any other int object.

5

EXAMPLE 2

After the declarations

typedef struct s1 { int x; } t1, *tp1;
typedef struct s2 { int x; } t2, *tp2;
type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type structs1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.

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The following obscure constructions

typedef signed int t;
typedef int plain;struct tag {unsigned t:4;
const t:5;
plain r:5;};
declare a typedef name t with type signed int, a typedef name plain with type int, and a structurewith three bit-field members, one named t that contains values in the range [0, 15], an unnamed constqualified bit-field which (if it could be accessed) would contain values in either the range [−15, +15] or[−16, +15], and one named r that contains values in one of the ranges [0, 31], [−15, +15], or [−16, +15].
(The choice of range is implementation-defined.) The first two bit-field declarations differ in that
unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
in an inner scope byt f(t (t));
long t;then a function f is declared with type ‘‘function returning signed int with one unnamed parameterwith type pointer to function returning signed int with one unnamed parameter with type signed
int’’, and an identifier t with type long int.

7

EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of thefollowing declarations of the signal function specify exactly the same type, the first without making useof any typedef names.
typedef void fv(int), (*pfv)(int);
void (*signal(int, void (*)(int)))(int);
fv *signal(int, fv *);pfv signal(int, pfv);

8

EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at thetime the typedef name is defined, not each time it is used:void copyt(int n){typedef int B[n];// B is n ints, n evaluated now
n += 1;
B a;// a is n ints, n without += 1
int b[n];// a and b are different sizesfor (int i = 1; i < n; i++)a[i-1] = b[i];}124Language§6.7.7

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6.7.8 Initialization
Syntax1

initializer:
assignment-expression{ initializer-list }{ initializer-list , }initializer-list:
designationopt initializer
initializer-list , designationopt initializer
designation:
designator-list =designator-list:
designator
designator-list designator
designator:[ constant-expression ]. identifier
Constraints

2

No initializer shall attempt to provide a value for an object not contained within the entity
being initialized.

3

The type of the entity to be initialized shall be an array of unknown size or an object typethat is not a variable length array type.

4

All the expressions in an initializer for an object that has static storage duration shall be
constant expressions or string literals.

5

If the declaration of an identifier has block scope, and the identifier has external orinternal linkage, the declaration shall have no initializer for the identifier.

6

If a designator has the form
[ constant-expression ]then the current object (defined below) shall have array type and the expression shall be
an integer constant expression. If the array is of unknown size, any nonnegative value isvalid.

7

If a designator has the form
. identifier
then the current object (defined below) shall have structure or union type and theidentifier shall be the name of a member of that type.
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Semantics
8

An initializer specifies the initial value stored in an object.

9

Except where explicitly stated otherwise, for the purposes of this subclause unnamed
members of objects of structure and union type do not participate in initialization.
Unnamed members of structure objects have indeterminate value even after initialization.

10

If an object that has automatic storage duration is not initialized explicitly, its value isindeterminate. If an object that has static storage duration is not initialized explicitly,then:— if it has pointer type, it is initialized to a null pointer;— if it has arithmetic type, it is initialized to (positive or unsigned) zero;— if it is an aggregate, every member is initialized (recursively) according to these rules;— if it is a union, the first named member is initialized (recursively) according to theserules.

11

The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
initial value of the object is that of the expression (after conversion); the same type
constraints and conversions as for simple assignment apply, taking the type of the scalar
to be the unqualified version of its declared type.

12

The rest of this subclause deals with initializers for objects that have aggregate or union
type.

13

The initializer for a structure or union object that has automatic storage duration shall beeither an initializer list as described below, or a single expression that has compatible
structure or union type. In the latter case, the initial value of the object, including
unnamed members, is that of the expression.

14

An array of character type may be initialized by a character string literal, optionallyenclosed in braces. Successive characters of the character string literal (including theterminating null character if there is room or if the array is of unknown size) initialize theelements of the array.

15

An array with element type compatible with wchar_t may be initialized by a wide
string literal, optionally enclosed in braces. Successive wide characters of the wide string
literal (including the terminating null wide character if there is room or if the array is of
unknown size) initialize the elements of the array.

16

Otherwise, the initializer for an object that has aggregate or union type shall be a braceenclosed list of initializers for the elements or named members.

17

Each brace-enclosed initializer list has an associated current object. When no
designations are present, subobjects of the current object are initialized in order according
to the type of the current object: array elements in increasing subscript order, structure
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members in declaration order, and the first named member of a union.129) In contrast, adesignation causes the following initializer to begin initialization of the subobject
described by the designator. Initialization then continues forward in order, beginningwith the next subobject after that described by the designator.130)
18

Each designator list begins its description with the current object associated with theclosest surrounding brace pair. Each item in the designator list (in order) specifies aparticular member of its current object and changes the current object for the next
designator (if any) to be that member.131) The current object that results at the end of thedesignator list is the subobject to be initialized by the following initializer.

19

The initialization shall occur in initializer list order, each initializer provided for aparticular subobject overriding any previously listed initializer for the same subobject;132)
all subobjects that are not initialized explicitly shall be initialized implicitly the same as
objects that have static storage duration.

20

If the aggregate or union contains elements or members that are aggregates or unions,these rules apply recursively to the subaggregates or contained unions. If the initializer ofa subaggregate or contained union begins with a left brace, the initializers enclosed bythat brace and its matching right brace initialize the elements or members of thesubaggregate or the contained union. Otherwise, only enough initializers from the list are
taken to account for the elements or members of the subaggregate or the first member ofthe contained union; any remaining initializers are left to initialize the next element or
member of the aggregate of which the current subaggregate or contained union is a part.

21

If there are fewer initializers in a brace-enclosed list than there are elements or membersof an aggregate, or fewer characters in a string literal used to initialize an array of known
size than there are elements in the array, the remainder of the aggregate shall be
initialized implicitly the same as objects that have static storage duration.

22

If an array of unknown size is initialized, its size is determined by the largest indexed
element with an explicit initializer. At the end of its initializer list, the array no longer
has incomplete type.

129) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
subobjects are initialized as usual, but the subaggregate or contained union does not become thecurrent object: current objects are associated only with brace-enclosed initializer lists.
130) After a union member is initialized, the next object is not the next member of the union; instead, it is
the next subobject of an object containing the union.
131) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated withthe surrounding brace pair. Note, too, that each separate designator list is independent.
132) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
not be evaluated at all.

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23

The order in which any side effects occur among the initialization list expressions isunspecified.133)

24

EXAMPLE 1

Provided that <complex.h> has been #included, the declarations

int i = 3.5;
double complex c = 5 + 3 * I;

define and initialize i with the value 3 and c with the value 5. 0 + i3. 0.

25

EXAMPLE 2

The declaration

int x[] = { 1, 3, 5 };defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
and there are three initializers.

26

EXAMPLE 3

The declaration

int y[4][3] = {{ 1, 3, 5 },{ 2, 4, 6 },{ 3, 5, 7 },};is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array objecty[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] andy[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could havebeen achieved byint y[4][3] = {1, 3, 5, 2, 4, 6, 3, 5, 7};
The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise thenext three are taken successively for y[1] and y[2].

27EXAMPLE 4

The declaration

int z[4][3] = {{ 1 }, { 2 }, { 3 }, { 4 }};initializes the first column of z as specified and initializes the rest with zeros.

28

EXAMPLE 5

The declaration

struct { int a[3], b; } w[] = { { 1 }, 2 };is a definition with an inconsistently bracketed initialization. It defines an array with two element
structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.

133) In particular, the evaluation order need not be the same as the order of subobject initialization.

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EXAMPLE 6

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The declaration

short q[4][3][2] = {{ 1 },{ 2, 3 },{ 4, 5, 6 }};contains an incompletely but consistently bracketed initialization. It defines a three-dimensional arrayobject: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing theirrespective two-dimensional subaggregates. If there had been more than six items in any of the lists, adiagnostic message would have been issued. The same initialization result could have been achieved by:short q[4][3][2] = {1, 0, 0, 0, 0, 0,
2, 3, 0, 0, 0, 0,
4, 5, 6};or by:
short q[4][3][2] = {{{ 1 },},{{ 2, 3 },},{{ 4, 5 },{ 6 },}};
in a fully bracketed form.

30

Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely tocause confusion.

31

EXAMPLE 7
declaration

One form of initialization that completes array types involves typedef names. Given thetypedef int A[];// OK - declared with block scope

the declaration
A a = { 1, 2 }, b = { 3, 4, 5 };is identical to
int a[] = { 1, 2 }, b[] = { 3, 4, 5 };due to the rules for incomplete types.

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EXAMPLE 8

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The declaration

char s[] = "abc", t[3] = "abc";
defines ‘‘plain’’ char array objects s and t whose elements are initialized with character string literals.
This declaration is identical tochar s[] = { 'a', 'b', 'c', '\0' },t[] = { 'a', 'b', 'c' };The contents of the arrays are modifiable. On the other hand, the declaration
char *p = "abc";
defines p with type ‘‘pointer to char’’ and initializes it to point to an object with type ‘‘array of char’’with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p tomodify the contents of the array, the behavior is undefined.

33

EXAMPLE 9
designators:

Arrays can be initialized to correspond to the elements of an enumeration by using

enum { member_one, member_two };const char *nm[] = {[member_two] = "member two",[member_one] = "member one",};

34

EXAMPLE 10

Structure members can be initialized to nonzero values without depending on their order:

div_t answer = { .quot = 2, .rem = -1 };35

EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
might be misunderstood:
struct { int a[3], b; } w[] ={ [0].a = {1}, [1].a[0] = 2 };36

EXAMPLE 12

Space can be ‘‘allocated’’ from both ends of an array by using a single designator:

int a[MAX] = {1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0};

37

In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is lessthan ten, some of the values provided by the first five initializers will be overridden by the second five.

38

EXAMPLE 13

Any member of a union can be initialized:

union { /* ... */ } u = { .any_member = 42 };Forward references: common definitions <stddef.h> (7.17).

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6.8 Statements and blocks
Syntax1

statement:labeled-statement
compound-statement
expression-statement
selection-statement
iteration-statement
jump-statement
Semantics

2

A statement specifies an action to be performed. Except as indicated, statements are
executed in sequence.

3

A block allows a set of declarations and statements to be grouped into one syntactic unit.
The initializers of objects that have automatic storage duration, and the variable length
array declarators of ordinary identifiers with block scope, are evaluated and the values are
stored in the objects (including storing an indeterminate value in objects without an
initializer) each time the declaration is reached in the order of execution, as if it were astatement, and within each declaration in the order that declarators appear.

4

A full expression is an expression that is not part of another expression or of a declarator.
Each of the following is a full expression: an initializer; the expression in an expression
statement; the controlling expression of a selection statement (if or switch); thecontrolling expression of a while or do statement; each of the (optional) expressions of
a for statement; the (optional) expression in a return statement. The end of a full
expression is a sequence point.
Forward references: expression and null statements (6.8.3), selection statements(6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).

6.8.1 Labeled statements
Syntax1

labeled-statement:
identifier : statementcase constant-expression : statement
default : statement
Constraints

2

A case or default label shall appear only in a switch statement. Further
constraints on such labels are discussed under the switch statement.

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Label names shall be unique within a function.
Semantics

4

Any statement may be preceded by a prefix that declares an identifier as a label name.
Labels in themselves do not alter the flow of control, which continues unimpeded acrossthem.
Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).

6.8.2 Compound statement
Syntax1

compound-statement:{ block-item-listopt }block-item-list:
block-item
block-item-list block-item
block-item:
declaration
statement
Semantics

2

A compound statement is a block.

6.8.3 Expression and null statements
Syntax1

expression-statement:
expressionopt ;Semantics

2

The expression in an expression statement is evaluated as a void expression for its side
effects.134)

3

A null statement (consisting of just a semicolon) performs no operations.

4

EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, thediscarding of its value may be made explicit by converting the expression to a void expression by means ofa cast:int p(int);/* ... */(void)p(0);134) Such as assignments, and function calls which have side effects.

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EXAMPLE 2

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In the program fragment

char *s;/* ... */while (*s++ != '\0');a null statement is used to supply an empty loop body to the iteration statement.

6

EXAMPLE 3
statement.

A null statement may also be used to carry a label just before the closing } of a compound

while (loop1) {/* ... */while (loop2) {/* ... */if (want_out)
goto end_loop1;/* ... */}/* ... */end_loop1: ;}Forward references: iteration statements (6.8.5).

6.8.4 Selection statements
Syntax1

selection-statement:if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement
Semantics

2

A selection statement selects among a set of statements depending on the value of acontrolling expression.

3

A selection statement is a block whose scope is a strict subset of the scope of its
enclosing block. Each associated substatement is also a block whose scope is a strict
subset of the scope of the selection statement.

6.8.4.1 The if statement
Constraints
1

The controlling expression of an if statement shall have scalar type.
Semantics

2

In both forms, the first substatement is executed if the expression compares unequal to 0.
In the else form, the second substatement is executed if the expression compares equal§6.8.4.1

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to 0. If the first substatement is reached via a label, the second substatement is not
executed.
3

An else is associated with the lexically nearest preceding if that is allowed by thesyntax.

6.8.4.2 The switch statement
Constraints
1

The controlling expression of a switch statement shall have integer type.

2

If a switch statement has an associated case or default label within the scope of an
identifier with a variably modified type, the entire switch statement shall be within thescope of that identifier.135)

3

The expression of each case label shall be an integer constant expression and no two of
the case constant expressions in the same switch statement shall have the same value
after conversion. There may be at most one default label in a switch statement.
(Any enclosed switch statement may have a default label or case constant
expressions with values that duplicate case constant expressions in the enclosing
switch statement.)
Semantics

4

A switch statement causes control to jump to, into, or past the statement that is theswitch body, depending on the value of a controlling expression, and on the presence of a
default label and the values of any case labels on or in the switch body. A case ordefault label is accessible only within the closest enclosing switch statement.

5

The integer promotions are performed on the controlling expression. The constant
expression in each case label is converted to the promoted type of the controlling
expression. If a converted value matches that of the promoted controlling expression,
control jumps to the statement following the matched case label. Otherwise, if there isa default label, control jumps to the labeled statement. If no converted case constant
expression matches and there is no default label, no part of the switch body is
executed.
Implementation limits

6

As discussed in 5.2.4.1, the implementation may limit the number of case values in aswitch statement.

135) That is, the declaration either precedes the switch statement, or it follows the last case ordefault label associated with the switch that is in the block containing the declaration.

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EXAMPLE

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In the artificial program fragment

switch (expr){
int i = 4;f(i);case 0:i = 17;/* falls through into default code */default:
printf("%d\n", i);}the object whose identifier is i exists with automatic storage duration (within the block) but is never
initialized, and thus if the controlling expression has a nonzero value, the call to the printf function willaccess an indeterminate value. Similarly, the call to the function f cannot be reached.

6.8.5 Iteration statements
Syntax1

iteration-statement:
while ( expression ) statement
do statement while ( expression ) ;for ( expressionopt ; expressionopt ; expressionopt ) statementfor ( declaration expressionopt ; expressionopt ) statement
Constraints

2

The controlling expression of an iteration statement shall have scalar type.

3

The declaration part of a for statement shall only declare identifiers for objects having
storage class auto or register.
Semantics

4

An iteration statement causes a statement called the loop body to be executed repeatedly
until the controlling expression compares equal to 0. The repetition occurs regardless ofwhether the loop body is entered from the iteration statement or by a jump.136)

5

An iteration statement is a block whose scope is a strict subset of the scope of its
enclosing block. The loop body is also a block whose scope is a strict subset of the scopeof the iteration statement.

136) Code jumped over is not executed. In particular, the controlling expression of a for or whilestatement is not evaluated before entering the loop body, nor is clause-1 of a for statement.

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6.8.5.1 The while statement
1

The evaluation of the controlling expression takes place before each execution of the loop
body.

6.8.5.2 The do statement
1

The evaluation of the controlling expression takes place after each execution of the loop
body.

6.8.5.3 The for statement
1

The statementfor ( clause-1 ; expression-2 ; expression-3 ) statement
behaves as follows: The expression expression-2 is the controlling expression that isevaluated before each execution of the loop body. The expression expression-3 isevaluated as a void expression after each execution of the loop body. If clause-1 is a
declaration, the scope of any identifiers it declares is the remainder of the declaration andthe entire loop, including the other two expressions; it is reached in the order of execution
before the first evaluation of the controlling expression. If clause-1 is an expression, it isevaluated as a void expression before the first evaluation of the controlling expression.137)

2

Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by anonzero constant.

6.8.6 Jump statements
Syntax1

jump-statement:
goto identifier ;continue ;break ;
return expressionopt ;Semantics

2

A jump statement causes an unconditional jump to another place.

137) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,such that execution of the loop continues until the expression compares equal to 0; and expression-3
specifies an operation (such as incrementing) that is performed after each iteration.

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6.8.6.1 The goto statement
Constraints
1

The identifier in a goto statement shall name a label located somewhere in the enclosing
function. A goto statement shall not jump from outside the scope of an identifier having
a variably modified type to inside the scope of that identifier.
Semantics

2

A goto statement causes an unconditional jump to the statement prefixed by the namedlabel in the enclosing function.

3

EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
following outline presents one possible approach to a problem based on these three assumptions:
1.

The general initialization code accesses objects only visible to the current function.

2.

The general initialization code is too large to warrant duplication.

3.

The code to determine the next operation is at the head of the loop. (To allow it to be reached bycontinue statements, for example.)/* ... */goto first_time;for (;;) {// determine next operation/* ... */if (need to reinitialize) {// reinitialize-only code/* ... */first_time:// general initialization code/* ... */continue;}// handle other operations/* ... */}§6.8.6.1

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EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
modified types. A jump within the scope, however, is permitted.
// invalid: going INTO scope of VLA.

goto lab3;{
double a[n];a[j] = 4.4;
lab3:
a[j] = 3.3;
goto lab4;
a[j] = 5.5;
lab4:
a[j] = 6.6;}
goto lab4;// valid: going WITHIN scope of VLA.

// invalid: going INTO scope of VLA.

6.8.6.2 The continue statement
Constraints
1

A continue statement shall appear only in or as a loop body.
Semantics

2

A continue statement causes a jump to the loop-continuation portion of the smallest
enclosing iteration statement; that is, to the end of the loop body. More precisely, in eachof the statements
while (/* ... */) {/* ... */continue;/* ... */contin: ;}do {/* ... */continue;/* ... */contin: ;} while (/* ... */);for (/* ... */) {/* ... */continue;/* ... */contin: ;}unless the continue statement shown is in an enclosed iteration statement (in whichcase it is interpreted within that statement), it is equivalent to goto contin;.138)

6.8.6.3 The break statement
Constraints
1

A break statement shall appear only in or as a switch body or loop body.
Semantics

2

A break statement terminates execution of the smallest enclosing switch or iteration
statement.

138) Following the contin: label is a null statement.

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6.8.6.4 The return statement
Constraints
1

A return statement with an expression shall not appear in a function whose return type
is void. A return statement without an expression shall only appear in a function
whose return type is void.
Semantics

2

A return statement terminates execution of the current function and returns control to
its caller. A function may have any number of return statements.

3

If a return statement with an expression is executed, the value of the expression isreturned to the caller as the value of the function call expression. If the expression has atype different from the return type of the function in which it appears, the value isconverted as if by assignment to an object having the return type of the function.139)

4

EXAMPLEIn:

struct s { double i; } f(void);
union {
struct {int f1;struct s f2;} u1;
struct {struct s f3;
int f4;} u2;} g;struct s f(void){
return g.u1.f2;}/* ... */g.u2.f3 = f();there is no undefined behavior, although there would be if the assignment were done directly (without using
a function call to fetch the value).

139) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
apply to the case of function return. The representation of floating-point values may have wider range
or precision and is determined by FLT_EVAL_METHOD. A cast may be used to remove this extra
range and precision.

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6.9 External definitions
Syntax1translation-unit:
external-declarationtranslation-unit external-declaration
external-declaration:function-definition
declaration
Constraints

2

The storage-class specifiers auto and register shall not appear in the declaration
specifiers in an external declaration.

3

There shall be no more than one external definition for each identifier declared withinternal linkage in a translation unit. Moreover, if an identifier declared with internal
linkage is used in an expression (other than as a part of the operand of a sizeof
operator whose result is an integer constant), there shall be exactly one external definition
for the identifier in the translation unit.
Semantics

4

As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
which consists of a sequence of external declarations. These are described as ‘‘external’’
because they appear outside any function (and hence have file scope). As discussed in
6.7, a declaration that also causes storage to be reserved for an object or a function namedby the identifier is a definition.

5

An external definition is an external declaration that is also a definition of a function(other than an inline definition) or an object. If an identifier declared with external
linkage is used in an expression (other than as part of the operand of a sizeof operator
whose result is an integer constant), somewhere in the entire program there shall be
exactly one external definition for the identifier; otherwise, there shall be no more than
one.140)140) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
external definition for it.

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6.9.1 Function definitions
Syntax1function-definition:
declaration-specifiers declarator declaration-listopt compound-statement
declaration-list:
declaration
declaration-list declaration
Constraints

2

The identifier declared in a function definition (which is the name of the function) shallhave a function type, as specified by the declarator portion of the function definition.141)

3

The return type of a function shall be void or an object type other than array type.

4

The storage-class specifier, if any, in the declaration specifiers shall be either extern or
static.

5

If the declarator includes a parameter type list, the declaration of each parameter shall
include an identifier, except for the special case of a parameter list consisting of a single
parameter of type void, in which case there shall not be an identifier. No declaration list
shall follow.

6

If the declarator includes an identifier list, each declaration in the declaration list shallhave at least one declarator, those declarators shall declare only identifiers from theidentifier list, and every identifier in the identifier list shall be declared. An identifier
declared as a typedef name shall not be redeclared as a parameter. The declarations in the
declaration list shall contain no storage-class specifier other than register and no
initializations.

141) The intent is that the type category in a function definition cannot be inherited from a typedef:
typedef int F(void);
F f, g;F f { /* ... */ }F g() { /* ... */ }int f(void) { /* ... */ }int g() { /* ... */ }F *e(void) { /* ... */ }F *((e))(void) { /* ... */ }int (*fp)(void);
F *Fp;§6.9.1// type F is ‘‘function with no parameters//
returning int’’// f and g both have type compatible with F// WRONG: syntax/constraint error// WRONG: declares that g returns a function// RIGHT: f has type compatible with F// RIGHT: g has type compatible with F// e returns a pointer to a function// same: parentheses irrelevant// fp points to a function that has type F// Fp points to a function that has type F

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Semantics
7

The declarator in a function definition specifies the name of the function being defined
and the identifiers of its parameters. If the declarator includes a parameter type list, thelist also specifies the types of all the parameters; such a declarator also serves as afunction prototype for later calls to the same function in the same translation unit. If thedeclarator includes an identifier list,142) the types of the parameters shall be declared in afollowing declaration list. In either case, the type of each parameter is adjusted as
described in 6.7.5.3 for a parameter type list; the resulting type shall be an object type.

8

If a function that accepts a variable number of arguments is defined without a parameter
type list that ends with the ellipsis notation, the behavior is undefined.

9

Each parameter has automatic storage duration. Its identifier is an lvalue, which is ineffect declared at the head of the compound statement that constitutes the function body(and therefore cannot be redeclared in the function body except in an enclosed block).
The layout of the storage for parameters is unspecified.

10

On entry to the function, the size expressions of each variably modified parameter are
evaluated and the value of each argument expression is converted to the type of thecorresponding parameter as if by assignment. (Array expressions and function
designators as arguments were converted to pointers before the call.)11

After all parameters have been assigned, the compound statement that constitutes the
body of the function definition is executed.

12

If the } that terminates a function is reached, and the value of the function call is used by
the caller, the behavior is undefined.

13

EXAMPLE 1

In the following:

extern int max(int a, int b){
return a > b ? a : b;}
extern is the storage-class specifier and int is the type specifier; max(int a, int b) is thefunction declarator; and{ return a > b ? a : b; }is the function body. The following similar definition uses the identifier-list form for the parameter
declarations:142) See ‘‘future language directions’’ (6.11.7).

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extern int max(a, b)
int a, b;{
return a > b ? a : b;}
Here int a, b; is the declaration list for the parameters. The difference between these two definitions isthat the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
to the function, whereas the second form does not.

14

EXAMPLE 2

To pass one function to another, one might say
int f(void);/* ... */g(f);Then the definition of g might readvoid g(int (*funcp)(void)){/* ... */(*funcp)(); /* or funcp(); ...
}*/or, equivalently,
void g(int func(void)){/* ... */func(); /* or (*func)(); ...
}*/6.9.2 External object definitions
Semantics
1

If the declaration of an identifier for an object has file scope and an initializer, thedeclaration is an external definition for the identifier.

2

A declaration of an identifier for an object that has file scope without an initializer, andwithout a storage-class specifier or with the storage-class specifier static, constitutes atentative definition. If a translation unit contains one or more tentative definitions for an
identifier, and the translation unit contains no external definition for that identifier, thenthe behavior is exactly as if the translation unit contains a file scope declaration of that
identifier, with the composite type as of the end of the translation unit, with an initializer
equal to 0.

3

If the declaration of an identifier for an object is a tentative definition and has internal
linkage, the declared type shall not be an incomplete type.

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EXAMPLE 1
int i1 = 1;
static int i2 = 2;
extern int i3 = 3;
int i4;static int i5;// definition, external linkage// definition, internal linkage// definition, external linkage// tentative definition, external linkage// tentative definition, internal linkage

int i1;
int i2;
int i3;
int i4;
int i5;// valid tentative definition, refers to previous// 6.2.2 renders undefined, linkage disagreement// valid tentative definition, refers to previous// valid tentative definition, refers to previous// 6.2.2 renders undefined, linkage disagreement

extern int i1;
extern int i2;
extern int i3;
extern int i4;
extern int i5;// refers to previous, whose linkage is external// refers to previous, whose linkage is internal// refers to previous, whose linkage is external// refers to previous, whose linkage is external// refers to previous, whose linkage is internal

EXAMPLE 2

If at the end of the translation unit containing

int i[];
the array i still has incomplete type, the implicit initializer causes it to have one element, which is set tozero on program startup.

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6.10 Preprocessing directives
Syntax1

preprocessing-file:groupopt
group:
group-partgroup group-partgroup-part:
if-section
control-line
text-line# non-directive
if-section:
if-group elif-groupsopt else-groupopt endif-line
if-group:# ifconstant-expression new-line groupopt# ifdef identifier new-line groupopt# ifndef identifier new-line groupopt
elif-groups:
elif-groupelif-groups elif-group§6.10

elif-group:# elifconstant-expression new-line groupopt

else-group:# elsenew-line groupopt

endif-line:# endif

new-line

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control-line:# include pp-tokens new-line# define identifier replacement-list new-line# define identifier lparen identifier-listopt )replacement-list new-line# define identifier lparen ... ) replacement-list new-line# define identifier lparen identifier-list , ... )replacement-list new-line# undef
identifier new-line# linepp-tokens new-line# errorpp-tokensopt new-line# pragma pp-tokensopt new-line#
new-linetext-line:
pp-tokensopt new-line
non-directive:
pp-tokens new-line
lparen:a ( character not immediately preceded by white-space
replacement-list:
pp-tokensopt
pp-tokens:
preprocessing-token
pp-tokens preprocessing-token
new-line:
the new-line character
Description
2

A preprocessing directive consists of a sequence of preprocessing tokens that satisfies thefollowing constraints: The first token in the sequence is a # preprocessing token that (atthe start of translation phase 4) is either the first character in the source file (optionallyafter white space containing no new-line characters) or that follows white spacecontaining at least one new-line character. The last token in the sequence is the first newline character that follows the first token in the sequence.143) A new-line character ends
the preprocessing directive even if it occurs within what would otherwise be an143) Thus, preprocessing directives are commonly called ‘‘lines’’. These ‘‘lines’’ have no other syntactic
significance, as all white space is equivalent except in certain situations during preprocessing (see the# character string literal creation operator in 6.10.3.2, for example).

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invocation of a function-like macro.
3

A text line shall not begin with a # preprocessing token. A non-directive shall not begin
with any of the directive names appearing in the syntax.

4

When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
sequence of preprocessing tokens to occur between the directive name and the following
new-line character.
Constraints

5

The only white-space characters that shall appear between preprocessing tokens within apreprocessing directive (from just after the introducing # preprocessing token throughjust before the terminating new-line character) are space and horizontal-tab (including
spaces that have replaced comments or possibly other white-space characters intranslation phase 3).
Semantics

6

The implementation can process and skip sections of source files conditionally, include
other source files, and replace macros. These capabilities are called preprocessing,
because conceptually they occur before translation of the resulting translation unit.

7

The preprocessing tokens within a preprocessing directive are not subject to macro
expansion unless otherwise stated.

8

EXAMPLEIn:#define EMPTY
EMPTY # include <file.h>the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
replaced.

6.10.1 Conditional inclusion
Constraints
1

The expression that controls conditional inclusion shall be an integer constant expression
except that: it shall not contain a cast; identifiers (including those lexically identical to
keywords) are interpreted as described below;144) and it may contain unary operator
expressions of the form144) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
either are or are not macro names — there simply are no keywords, enumeration constants, etc.

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defined identifierordefined ( identifier )which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it ispredefined or if it has been the subject of a #define preprocessing directive without anintervening #undef directive with the same subject identifier), 0 if it is not.
2

Each preprocessing token that remains (in the list of preprocessing tokens that will
become the controlling expression) after all macro replacements have occurred shall be in
the lexical form of a token (6.4).

Semantics
3

Preprocessing directives of the forms# ifconstant-expression new-line groupopt# elif constant-expression new-line groupopt
check whether the controlling constant expression evaluates to nonzero.

4

Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
the controlling constant expression are replaced (except for those macro names modified
by the defined unary operator), just as in normal text. If the token defined isgenerated as a result of this replacement process or use of the defined unary operator
does not match one of the two specified forms prior to macro replacement, the behavior isundefined. After all replacements due to macro expansion and the defined unaryoperator have been performed, all remaining identifiers (including those lexically
identical to keywords) are replaced with the pp-number 0, and then each preprocessing
token is converted into a token. The resulting tokens compose the controlling constant
expression which is evaluated according to the rules of 6.6. For the purposes of thistoken conversion and evaluation, all signed integer types and all unsigned integer types
act as if they have the same representation as, respectively, the types intmax_t anduintmax_t defined in the header <stdint.h>.145) This includes interpretingcharacter constants, which may involve converting escape sequences into execution
character set members. Whether the numeric value for these character constants matches
the value obtained when an identical character constant occurs in an expression (otherthan within a #if or #elif directive) is implementation-defined.146) Also, whether asingle-character character constant may have a negative value is implementation-defined.

5

Preprocessing directives of the forms

145) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
0x8000 is signed and positive within a #if expression even though it would be unsigned intranslation phase 7.

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ISO/IEC 9899:TC3# ifdef identifier new-line groupopt# ifndef identifier new-line groupopt
check whether the identifier is or is not currently defined as a macro name. Theirconditions are equivalent to #if defined identifier and #if !defined identifier
respectively.
6

Each directive’s condition is checked in order. If it evaluates to false (zero), the groupthat it controls is skipped: directives are processed only through the name that determines
the directive in order to keep track of the level of nested conditionals; the rest of thedirectives’ preprocessing tokens are ignored, as are the other preprocessing tokens in thegroup. Only the first group whose control condition evaluates to true (nonzero) is
processed. If none of the conditions evaluates to true, and there is a #else directive, thegroup controlled by the #else is processed; lacking a #else directive, all the groups
until the #endif are skipped.147)
Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
integer types (7.18.1.5).

6.10.2 Source file inclusion
Constraints
1

A #include directive shall identify a header or source file that can be processed by the
implementation.
Semantics

2

A preprocessing directive of the form
# include <h-char-sequence> new-line
searches a sequence of implementation-defined places for a header identified uniquely by
the specified sequence between the < and > delimiters, and causes the replacement of that
directive by the entire contents of the header. How the places are specified or the header
identified is implementation-defined.

3

A preprocessing directive of the form

146) Thus, the constant expression in the following #if directive and if statement is not guaranteed toevaluate to the same value in these two contexts.
#if 'z' - 'a' == 25
if ('z' - 'a' == 25)
147) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
before the terminating new-line character. However, comments may appear anywhere in a source file,including within a preprocessing directive.

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causes the replacement of that directive by the entire contents of the source file identified
by the specified sequence between the " delimiters. The named source file is searched
for in an implementation-defined manner. If this search is not supported, or if the searchfails, the directive is reprocessed as if it read# include <h-char-sequence> new-linewith the identical contained sequence (including > characters, if any) from the original
directive.
4

A preprocessing directive of the form
# include pp-tokens new-line(that does not match one of the two previous forms) is permitted. The preprocessing
tokens after include in the directive are processed just as in normal text. (Eachidentifier currently defined as a macro name is replaced by its replacement list of
preprocessing tokens.) The directive resulting after all replacements shall match one of
the two previous forms.148) The method by which a sequence of preprocessing tokens
between a < and a > preprocessing token pair or a pair of " characters is combined into asingle header name preprocessing token is implementation-defined.

5

The implementation shall provide unique mappings for sequences consisting of one ormore nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
first character shall not be a digit. The implementation may ignore distinctions ofalphabetical case and restrict the mapping to eight significant characters before theperiod.

6

A #include preprocessing directive may appear in a source file that has been readbecause of a #include directive in another file, up to an implementation-defined
nesting limit (see 5.2.4.1).

7

EXAMPLE 1

The most common uses of #include preprocessing directives are as in the following:#include <stdio.h>#include "myprog.h"8EXAMPLE 2

This illustrates macro-replaced #include directives:

148) Note that adjacent string literals are not concatenated into a single string literal (see the translation
phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.

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#if VERSION == 1
#define INCFILE#elif VERSION == 2
#define INCFILE#else#define INCFILE#endif#include INCFILE

ISO/IEC 9899:TC3"vers1.h""vers2.h"// and so on"versN.h"

Forward references: macro replacement (6.10.3).

6.10.3 Macro replacement
Constraints
1

Two replacement lists are identical if and only if the preprocessing tokens in both havethe same number, ordering, spelling, and white-space separation, where all white-space
separations are considered identical.

2

An identifier currently defined as an object-like macro shall not be redefined by another#define preprocessing directive unless the second definition is an object-like macrodefinition and the two replacement lists are identical. Likewise, an identifier currently
defined as a function-like macro shall not be redefined by another #define
preprocessing directive unless the second definition is a function-like macro definition
that has the same number and spelling of parameters, and the two replacement lists are
identical.

3

There shall be white-space between the identifier and the replacement list in the definitionof an object-like macro.

4

If the identifier-list in the macro definition does not end with an ellipsis, the number ofarguments (including those arguments consisting of no preprocessing tokens) in an
invocation of a function-like macro shall equal the number of parameters in the macrodefinition. Otherwise, there shall be more arguments in the invocation than there areparameters in the macro definition (excluding the ...). There shall exist a )preprocessing token that terminates the invocation.

5

The identifier _ _VA_ARGS_ _ shall occur only in the replacement-list of a function-likemacro that uses the ellipsis notation in the parameters.

6

A parameter identifier in a function-like macro shall be uniquely declared within its
scope.
Semantics

7

The identifier immediately following the define is called the macro name. There is one
name space for macro names. Any white-space characters preceding or following the
replacement list of preprocessing tokens are not considered part of the replacement list
for either form of macro.
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8

If a # preprocessing token, followed by an identifier, occurs lexically at the point at whicha preprocessing directive could begin, the identifier is not subject to macro replacement.

9

A preprocessing directive of the form
# define identifier replacement-list new-line
defines an object-like macro that causes each subsequent instance of the macro name149)
to be replaced by the replacement list of preprocessing tokens that constitute theremainder of the directive. The replacement list is then rescanned for more macro names
as specified below.

10

A preprocessing directive of the form
# define identifier lparen identifier-listopt ) replacement-list new-line# define identifier lparen ... ) replacement-list new-line# define identifier lparen identifier-list , ... ) replacement-list new-line
defines a function-like macro with parameters, whose use is similar syntactically to afunction call. The parameters are specified by the optional list of identifiers, whose scope
extends from their declaration in the identifier list until the new-line character thatterminates the #define preprocessing directive. Each subsequent instance of thefunction-like macro name followed by a ( as the next preprocessing token introduces thesequence of preprocessing tokens that is replaced by the replacement list in the definition(an invocation of the macro). The replaced sequence of preprocessing tokens isterminated by the matching ) preprocessing token, skipping intervening matched pairs ofleft and right parenthesis preprocessing tokens. Within the sequence of preprocessing
tokens making up an invocation of a function-like macro, new-line is considered a normal
white-space character.

11

The sequence of preprocessing tokens bounded by the outside-most matching parentheses
forms the list of arguments for the function-like macro. The individual arguments within
the list are separated by comma preprocessing tokens, but comma preprocessing tokens
between matching inner parentheses do not separate arguments. If there are sequences ofpreprocessing tokens within the list of arguments that would otherwise act aspreprocessing directives,150) the behavior is undefined.

12

If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
including any separating comma preprocessing tokens, are merged to form a single item:
the variable arguments. The number of arguments so combined is such that, following149) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
are never scanned for macro names or parameters.
150) Despite the name, a non-directive is a preprocessing directive.

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merger, the number of arguments is one more than the number of parameters in the macrodefinition (excluding the ...).

6.10.3.1 Argument substitution
1

After the arguments for the invocation of a function-like macro have been identified,argument substitution takes place. A parameter in the replacement list, unless precededby a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
replaced by the corresponding argument after all macros contained therein have been
expanded. Before being substituted, each argument’s preprocessing tokens arecompletely macro replaced as if they formed the rest of the preprocessing file; no otherpreprocessing tokens are available.

2

An identifier _ _VA_ARGS_ _ that occurs in the replacement list shall be treated as if itwere a parameter, and the variable arguments shall form the preprocessing tokens used toreplace it.

6.10.3.2 The # operator
Constraints
1

Each # preprocessing token in the replacement list for a function-like macro shall befollowed by a parameter as the next preprocessing token in the replacement list.
Semantics

2

If, in the replacement list, a parameter is immediately preceded by a # preprocessing
token, both are replaced by a single character string literal preprocessing token that
contains the spelling of the preprocessing token sequence for the correspondingargument. Each occurrence of white space between the argument’s preprocessing tokens
becomes a single space character in the character string literal. White space before thefirst preprocessing token and after the last preprocessing token composing the argument
is deleted. Otherwise, the original spelling of each preprocessing token in the argument
is retained in the character string literal, except for special handling for producing thespelling of string literals and character constants: a \ character is inserted before each "and \ character of a character constant or string literal (including the delimiting "characters), except that it is implementation-defined whether a \ character is inserted
before the \ character beginning a universal character name. If the replacement that
results is not a valid character string literal, the behavior is undefined. The character
string literal corresponding to an empty argument is "". The order of evaluation of # and## operators is unspecified.

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6.10.3.3 The ## operator
Constraints
1

A ## preprocessing token shall not occur at the beginning or at the end of a replacement
list for either form of macro definition.
Semantics

2

If, in the replacement list of a function-like macro, a parameter is immediately preceded
or followed by a ## preprocessing token, the parameter is replaced by the correspondingargument’s preprocessing token sequence; however, if an argument consists of no
preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
instead.151)

3

For both object-like and function-like macro invocations, before the replacement list isreexamined for more macro names to replace, each instance of a ## preprocessing token
in the replacement list (not from an argument) is deleted and the preceding preprocessing
token is concatenated with the following preprocessing token. Placemarker
preprocessing tokens are handled specially: concatenation of two placemarkers results ina single placemarker preprocessing token, and concatenation of a placemarker with a
non-placemarker preprocessing token results in the non-placemarker preprocessing token.
If the result is not a valid preprocessing token, the behavior is undefined. The resulting
token is available for further macro replacement. The order of evaluation of ## operators
is unspecified.

4

EXAMPLEIn the following fragment:#define hash_hash # ## ##define mkstr(a) # a#define in_between(a) mkstr(a)#define join(c, d) in_between(c hash_hash d)char p[] = join(x, y); // equivalent to// char p[] = "x ## y";
The expansion produces, at various stages:join(x, y)
in_between(x hash_hash y)in_between(x ## y)
mkstr(x ## y)"x ## y"In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
this new token is not the ## operator.

151) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities thatexist only within translation phase 4.

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6.10.3.4 Rescanning and further replacement
1

After all parameters in the replacement list have been substituted and # and ##processing has taken place, all placemarker preprocessing tokens are removed. Then, theresulting preprocessing token sequence is rescanned, along with all subsequent
preprocessing tokens of the source file, for more macro names to replace.

2

If the name of the macro being replaced is found during this scan of the replacement list
(not including the rest of the source file’s preprocessing tokens), it is not replaced.
Furthermore, if any nested replacements encounter the name of the macro being replaced,
it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
available for further replacement even if they are later (re)examined in contexts in whichthat macro name preprocessing token would otherwise have been replaced.

3

The resulting completely macro-replaced preprocessing token sequence is not processed
as a preprocessing directive even if it resembles one, but all pragma unary operator
expressions within it are then processed as specified in 6.10.9 below.

6.10.3.5 Scope of macro definitions
1

A macro definition lasts (independent of block structure) until a corresponding #undef
directive is encountered or (if none is encountered) until the end of the preprocessing
translation unit. Macro definitions have no significance after translation phase 4.

2

A preprocessing directive of the form
# undef identifier new-line
causes the specified identifier no longer to be defined as a macro name. It is ignored if
the specified identifier is not currently defined as a macro name.

3

EXAMPLE 1

The simplest use of this facility is to define a ‘‘manifest constant’’, as in#define TABSIZE 100
int table[TABSIZE];

4EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
It has the advantages of working for any compatible types of the arguments and of generating in-line code
without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
arguments a second time (including side effects) and generating more code than a function if invoked
several times. It also cannot have its address taken, as it has none.
#define max(a, b) ((a) > (b) ? (a) : (b))
The parentheses ensure that the arguments and the resulting expression are bound properly.

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To illustrate the rules for redefinition and reexamination, the sequence#define x
3#define f(a)f(x * (a))#undef x#define x
2#define gf#define z
z[0]#define hg(~#define m(a)a(w)#define w
0,1#define t(a)a#define p()int#define q(x)x#define r(x,y) x ## y#define str(x) # xf(y+1) + f(f(z)) % t(t(g)(0) + t)(1);g(x+(3,4)-w) | h 5) & m(f)^m(m);p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };char c[2][6] = { str(hello), str() };results inf(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
int i[] = { 1, 23, 4, 5, };char c[2][6] = { "hello", "" };6

EXAMPLE 4
sequence

To illustrate the rules for creating character string literals and concatenating tokens, the#define str(s)# s#define xstr(s)str(s)#define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \x ## s, x ## t)#define INCFILE(n) vers ## n#define glue(a, b) a ## b
#define xglue(a, b) glue(a, b)#define HIGHLOW"hello"#define LOW
LOW ", world"
debug(1, 2);
fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away== 0) str(: @\n), s);#include xstr(INCFILE(2).h)glue(HIGH, LOW);
xglue(HIGH, LOW)
results in

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printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
fputs("strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",s);#include "vers2.h"(after macro replacement, before file access)"hello";"hello" ", world"or, after concatenation of the character string literals,
printf("x1= %d, x2= %s", x1, x2);
fputs("strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",s);#include "vers2.h"(after macro replacement, before file access)"hello";"hello, world"
Space around the # and ## tokens in the macro definition is optional.

7

EXAMPLE 5

To illustrate the rules for placemarker preprocessing tokens, the sequence#define t(x,y,z) x ## y ## z
int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),t(10,,), t(,11,), t(,,12), t(,,) };results inint j[] = { 123, 45, 67, 89,
10, 11, 12, };8

EXAMPLE 6

To demonstrate the redefinition rules, the following sequence is valid.

#define OBJ_LIKE(1-1)#define OBJ_LIKE/* white space */ (1-1) /* other */#define FUNC_LIKE(a)( a )#define FUNC_LIKE( a )( /* note the white space */ \a /* other stuff on this line*/ )But the following redefinitions are invalid:#define OBJ_LIKE(0)// different token sequence#define OBJ_LIKE(1 - 1) // different white space#define FUNC_LIKE(b) ( a ) // different parameter usage#define FUNC_LIKE(b) ( b ) // different parameter spelling

9

EXAMPLE 7

Finally, to show the variable argument list macro facilities:#define debug(...)
fprintf(stderr, _ _VA_ARGS_ _)#define showlist(...)
puts(#_ _VA_ARGS_ _)#define report(test, ...) ((test)?puts(#test):\printf(_ _VA_ARGS_ _))debug("Flag");debug("X = %d\n", x);
showlist(The first, second, and third items.);
report(x>y, "x is %d but y is %d", x, y);§6.10.3.5

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results in
fprintf(stderr, "Flag" );fprintf(stderr, "X = %d\n", x );puts( "The first, second, and third items." );((x>y)?puts("x>y"):printf("x is %d but y is %d", x, y));6.10.4 Line control
Constraints
1

The string literal of a #line directive, if present, shall be a character string literal.
Semantics

2

The line number of the current source line is one greater than the number of new-line
characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
file to the current token.

3

A preprocessing directive of the form
# line digit-sequence new-line
causes the implementation to behave as if the following sequence of source lines begins
with a source line that has a line number as specified by the digit sequence (interpreted asa decimal integer). The digit sequence shall not specify zero, nor a number greater than2147483647.

4

A preprocessing directive of the form
# line digit-sequence "s-char-sequenceopt" new-line
sets the presumed line number similarly and changes the presumed name of the source
file to be the contents of the character string literal.

5

A preprocessing directive of the form
# line pp-tokens new-line(that does not match one of the two previous forms) is permitted. The preprocessing
tokens after line on the directive are processed just as in normal text (each identifier
currently defined as a macro name is replaced by its replacement list of preprocessing
tokens). The directive resulting after all replacements shall match one of the two
previous forms and is then processed as appropriate.

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6.10.5 Error directive
Semantics
1

A preprocessing directive of the form
# error pp-tokensopt new-line
causes the implementation to produce a diagnostic message that includes the specified
sequence of preprocessing tokens.

6.10.6 Pragma directive
Semantics
1

A preprocessing directive of the form
# pragma pp-tokensopt new-line
where the preprocessing token STDC does not immediately follow pragma in the
directive (prior to any macro replacement)152) causes the implementation to behave in an
implementation-defined manner. The behavior might cause translation to fail or cause thetranslator or the resulting program to behave in a non-conforming manner. Any such
pragma that is not recognized by the implementation is ignored.

2

If the preprocessing token STDC does immediately follow pragma in the directive (prior
to any macro replacement), then no macro replacement is performed on the directive, andthe directive shall have one of the following forms153) whose meanings are described
elsewhere:#pragma STDC FP_CONTRACT on-off-switch#pragma STDC FENV_ACCESS on-off-switch#pragma STDC CX_LIMITED_RANGE on-off-switch
on-off-switch: one of
ON
OFF

DEFAULT

Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma(7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).

152) An implementation is not required to perform macro replacement in pragmas, but it is permitted
except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
but is not required to.
153) See ‘‘future language directions’’ (6.11.8).

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6.10.7 Null directive
Semantics
1

A preprocessing directive of the form
# new-line
has no effect.

6.10.8 Predefined macro names
1

The following macro names154) shall be defined by the implementation:_ _DATE_ _ The date of translation of the preprocessing translation unit: a character
string literal of the form "Mmm dd yyyy", where the names of themonths are the same as those generated by the asctime function, and thefirst character of dd is a space character if the value is less than 10. If thedate of translation is not available, an implementation-defined valid dateshall be supplied.
_ _FILE_ _ The presumed name of the current source file (a character string literal).155)_ _LINE_ _ The presumed line number (within the current source file) of the current
source line (an integer constant).155)_ _STDC_ _ The integer constant 1, intended to indicate a conforming implementation.
_ _STDC_HOSTED_ _ The integer constant 1 if the implementation is a hosted
implementation or the integer constant 0 if it is not.
_ _STDC_MB_MIGHT_NEQ_WC_ _ The integer constant 1, intended to indicate that, inthe encoding for wchar_t, a member of the basic character set need nothave a code value equal to its value when used as the lone character in an
integer character constant.

_ _STDC_VERSION_ _ The integer constant 199901L.156)_ _TIME_ _ The time of translation of the preprocessing translation unit: a character
string literal of the form "hh:mm:ss" as in the time generated by theasctime function. If the time of translation is not available, animplementation-defined valid time shall be supplied.

154) See ‘‘future language directions’’ (6.11.9).
155) The presumed source file name and line number can be changed by the #line directive.
156) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
ISO/IEC 9899/AMD1:1995. The intention is that this will remain an integer constant of type long
int that is increased with each revision of this International Standard.

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2

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The following macro names are conditionally defined by the implementation:_ _STDC_IEC_559_ _ The integer constant 1, intended to indicate conformance to thespecifications in annex F (IEC 60559 floating-point arithmetic).
_ _STDC_IEC_559_COMPLEX_ _ The integer constant 1, intended to indicate
adherence to the specifications in informative annex G (IEC 60559
compatible complex arithmetic).
_ _STDC_ISO_10646_ _ An integer constant of the form yyyymmL (for example,
199712L). If this symbol is defined, then every character in the Unicode
required set, when stored in an object of type wchar_t, has the samevalue as the short identifier of that character. The Unicode required set
consists of all the characters that are defined by ISO/IEC 10646, along withall amendments and technical corrigenda, as of the specified year andmonth.

3

The values of the predefined macros (except for _ _FILE_ _ and _ _LINE_ _) remain
constant throughout the translation unit.

4

None of these macro names, nor the identifier defined, shall be the subject of a#define or a #undef preprocessing directive. Any other predefined macro names
shall begin with a leading underscore followed by an uppercase letter or a second
underscore.

5

The implementation shall not predefine the macro _ _cplusplus, nor shall it define itin any standard header.
Forward references: the asctime function (7.23.3.1), standard headers (7.1.2).

6.10.9 Pragma operator
Semantics
1

A unary operator expression of the form:_Pragma ( string-literal )is processed as follows: The string literal is destringized by deleting the L prefix, if
present, deleting the leading and trailing double-quotes, replacing each escape sequence\" by a double-quote, and replacing each escape sequence \\ by a single backslash. The
resulting sequence of characters is processed through translation phase 3 to produce
preprocessing tokens that are executed as if they were the pp-tokens in a pragma
directive. The original four preprocessing tokens in the unary operator expression are
removed.

2

EXAMPLEA directive of the form:#pragma listing on "..\listing.dir"
can also be expressed as:§6.10.9

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WG14/N1256_Pragma ( "listing on \"..\\listing.dir\"" )The latter form is processed in the same way whether it appears literally as shown, or results from macro
replacement, as in:#define LISTING(x) PRAGMA(listing on #x)#define PRAGMA(x) _Pragma(#x)
LISTING ( ..\listing.dir )162

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6.11 Future language directions
6.11.1 Floating types
1

Future standardization may include additional floating-point types, including those withgreater range, precision, or both than long double.

6.11.2 Linkages of identifiers
1

Declaring an identifier with internal linkage at file scope without the static storageclass specifier is an obsolescent feature.

6.11.3 External names
1

Restriction of the significance of an external name to fewer than 255 characters(considering each universal character name or extended source character as a single
character) is an obsolescent feature that is a concession to existing implementations.

6.11.4 Character escape sequences
1

Lowercase letters as escape sequences are reserved for future standardization. Other
characters may be used in extensions.

6.11.5 Storage-class specifiers
1

The placement of a storage-class specifier other than at the beginning of the declaration
specifiers in a declaration is an obsolescent feature.

6.11.6 Function declarators
1

The use of function declarators with empty parentheses (not prototype-format parameter
type declarators) is an obsolescent feature.

6.11.7 Function definitions
1

The use of function definitions with separate parameter identifier and declaration lists(not prototype-format parameter type and identifier declarators) is an obsolescent feature.

6.11.8 Pragma directives
1

Pragmas whose first preprocessing token is STDC are reserved for future standardization.

6.11.9 Predefined macro names
1

Macro names beginning with _ _STDC_ are reserved for future standardization.

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7. Library
7.1 Introduction
7.1.1 Definitions of terms
1

A string is a contiguous sequence of characters terminated by and including the first nullcharacter. The term multibyte string is sometimes used instead to emphasize special
processing given to multibyte characters contained in the string or to avoid confusion
with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)character. The length of a string is the number of bytes preceding the null character andthe value of a string is the sequence of the values of the contained characters, in order.

2

The decimal-point character is the character used by functions that convert floating-point
numbers to or from character sequences to denote the beginning of the fractional part ofsuch character sequences.157) It is represented in the text and examples by a period, but
may be changed by the setlocale function.

3

A null wide character is a wide character with code value zero.

4

A wide string is a contiguous sequence of wide characters terminated by and including
the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
addressed) wide character. The length of a wide string is the number of wide characters
preceding the null wide character and the value of a wide string is the sequence of codevalues of the contained wide characters, in order.

5

A shift sequence is a contiguous sequence of bytes within a multibyte string that(potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have acorresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
character.158)
Forward references: character handling (7.4), the setlocale function (7.11.1.1).

157) The functions that make use of the decimal-point character are the numeric conversion functions(7.20.1, 7.24.4.1) and the formatted input/output functions (7.19.6, 7.24.2).
158) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
sequence of maximum length. Whether these counts provide for more than one shift sequence is theimplementation’s choice.

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7.1.2 Standard headers
1

Each library function is declared, with a type that includes a prototype, in a header,159)
whose contents are made available by the #include preprocessing directive. The
header declares a set of related functions, plus any necessary types and additional macros
needed to facilitate their use. Declarations of types described in this clause shall notinclude type qualifiers, unless explicitly stated otherwise.

2

The standard headers are<assert.h><complex.h><ctype.h><errno.h><fenv.h><float.h><inttypes.h><iso646.h><limits.h><locale.h><math.h><setjmp.h><signal.h><stdarg.h><stdbool.h><stddef.h><stdint.h><stdio.h><stdlib.h><string.h><tgmath.h><time.h><wchar.h><wctype.h>3

If a file with the same name as one of the above < and > delimited sequences, notprovided as part of the implementation, is placed in any of the standard places that are
searched for included source files, the behavior is undefined.

4Standard headers may be included in any order; each may be included more than once ina given scope, with no effect different from being included only once, except that theeffect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
used, a header shall be included outside of any external declaration or definition, and it
shall first be included before the first reference to any of the functions or objects it
declares, or to any of the types or macros it defines. However, if an identifier is declaredor defined in more than one header, the second and subsequent associated headers may be
included after the initial reference to the identifier. The program shall not have any
macros with names lexically identical to keywords currently defined prior to theinclusion.

5

Any definition of an object-like macro described in this clause shall expand to code that isfully protected by parentheses where necessary, so that it groups in an arbitrary
expression as if it were a single identifier.

6

Any declaration of a library function shall have external linkage.

7

A summary of the contents of the standard headers is given in annex B.
Forward references: diagnostics (7.2).

159) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
necessarily valid source file names.

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7.1.3 Reserved identifiers
1

Each header declares or defines all identifiers listed in its associated subclause, andoptionally declares or defines identifiers listed in its associated future library directions
subclause and identifiers which are always reserved either for any use or for use as file
scope identifiers.
— All identifiers that begin with an underscore and either an uppercase letter or another
underscore are always reserved for any use.
— All identifiers that begin with an underscore are always reserved for use as identifierswith file scope in both the ordinary and tag name spaces.
— Each macro name in any of the following subclauses (including the future library
directions) is reserved for use as specified if any of its associated headers is included;
unless explicitly stated otherwise (see 7.1.4).
— All identifiers with external linkage in any of the following subclauses (including thefuture library directions) are always reserved for use as identifiers with external
linkage.160)— Each identifier with file scope listed in any of the following subclauses (including thefuture library directions) is reserved for use as a macro name and as an identifier withfile scope in the same name space if any of its associated headers is included.

2

No other identifiers are reserved. If the program declares or defines an identifier in acontext in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
identifier as a macro name, the behavior is undefined.

3

If the program removes (with #undef) any macro definition of an identifier in the firstgroup listed above, the behavior is undefined.

7.1.4 Use of library functions
1

Each of the following statements applies unless explicitly stated otherwise in the detailed
descriptions that follow: If an argument to a function has an invalid value (such as a value
outside the domain of the function, or a pointer outside the address space of the program,or a null pointer, or a pointer to non-modifiable storage when the corresponding
parameter is not const-qualified) or a type (after promotion) not expected by a function
with variable number of arguments, the behavior is undefined. If a function argument is
described as being an array, the pointer actually passed to the function shall have a value
such that all address computations and accesses to objects (that would be valid if thepointer did point to the first element of such an array) are in fact valid. Any function
declared in a header may be additionally implemented as a function-like macro defined in160) The list of reserved identifiers with external linkage includes errno, math_errhandling,
setjmp, and va_end.

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the header, so if a library function is declared explicitly when its header is included, oneof the techniques shown below can be used to ensure the declaration is not affected bysuch a macro. Any macro definition of a function can be suppressed locally by enclosing
the name of the function in parentheses, because the name is then not followed by the leftparenthesis that indicates expansion of a macro function name. For the same syntactic
reason, it is permitted to take the address of a library function even if it is also defined asa macro.161) The use of #undef to remove any macro definition will also ensure that an
actual function is referred to. Any invocation of a library function that is implemented asa macro shall expand to code that evaluates each of its arguments exactly once, fully
protected by parentheses where necessary, so it is generally safe to use arbitrary
expressions as arguments.162) Likewise, those function-like macros described in thefollowing subclauses may be invoked in an expression anywhere a function with acompatible return type could be called.163) All object-like macros listed as expanding tointeger constant expressions shall additionally be suitable for use in #if preprocessing
directives.
2

Provided that a library function can be declared without reference to any type defined in aheader, it is also permissible to declare the function and use it without including its
associated header.

3

There is a sequence point immediately before a library function returns.

4

The functions in the standard library are not guaranteed to be reentrant and may modify
objects with static storage duration.164)

161) This means that an implementation shall provide an actual function for each library function, even if it
also provides a macro for that function.
162) Such macros might not contain the sequence points that the corresponding function calls do.
163) Because external identifiers and some macro names beginning with an underscore are reserved,
implementations may provide special semantics for such names. For example, the identifier_BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, theappropriate header could specify#define abs(x) _BUILTIN_abs(x)for a compiler whose code generator will accept it.
In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
function may write#undef abs
whether the implementation’s header provides a macro implementation of abs or a built-in
implementation. The prototype for the function, which precedes and is hidden by any macrodefinition, is thereby revealed also.
164) Thus, a signal handler cannot, in general, call standard library functions.

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The function atoi may be used in any of several ways:— by use of its associated header (possibly generating a macro expansion)#include <stdlib.h>const char *str;/* ... */i = atoi(str);— by use of its associated header (assuredly generating a true function reference)#include <stdlib.h>#undef atoi
const char *str;/* ... */i = atoi(str);or#include <stdlib.h>const char *str;/* ... */i = (atoi)(str);— by explicit declaration
extern int atoi(const char *);const char *str;/* ... */i = atoi(str);

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7.2 Diagnostics <assert.h>
1

The header <assert.h> defines the assert macro and refers to another macro,
NDEBUG
which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
point in the source file where <assert.h> is included, the assert macro is defined
simply as#define assert(ignore) ((void)0)
The assert macro is redefined according to the current state of NDEBUG each time that<assert.h> is included.

2

The assert macro shall be implemented as a macro, not as an actual function. If themacro definition is suppressed in order to access an actual function, the behavior isundefined.

7.2.1 Program diagnostics
7.2.1.1 The assert macro
Synopsis1#include <assert.h>void assert(scalar expression);
Description

2

The assert macro puts diagnostic tests into programs; it expands to a void expression.
When it is executed, if expression (which shall have a scalar type) is false (that is,compares equal to 0), the assert macro writes information about the particular call thatfailed (including the text of the argument, the name of the source file, the source line
number, and the name of the enclosing function — the latter are respectively the values ofthe preprocessing macros _ _FILE_ _ and _ _LINE_ _ and of the identifier_ _func_ _) on the standard error stream in an implementation-defined format.165) It
then calls the abort function.
Returns3

The assert macro returns no value.
Forward references: the abort function (7.20.4.1).

165) The message written might be of the form:
Assertion failed: expression, function abc, file xyz, line nnn.

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7.3 Complex arithmetic <complex.h>7.3.1 Introduction
1

The header <complex.h> defines macros and declares functions that support complex
arithmetic.166) Each synopsis specifies a family of functions consisting of a principal
function with one or more double complex parameters and a double complex or
double return value; and other functions with the same name but with f and l suffixes
which are corresponding functions with float and long double parameters andreturn values.

2

The macrocomplexexpands to _Complex; the macro_Complex_I
expands to a constant expression of type const float _Complex, with the value ofthe imaginary unit.167)

3

The macros
imaginaryand_Imaginary_I
are defined if and only if the implementation supports imaginary types;168) if defined,
they expand to _Imaginary and a constant expression of type const float_Imaginary with the value of the imaginary unit.

4

The macroI
expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is notdefined, I shall expand to _Complex_I.

5

Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps thenredefine the macros complex, imaginary, and I.
Forward references: IEC 60559-compatible complex arithmetic (annex G).

166) See ‘‘future library directions’’ (7.26.1).
167) The imaginary unit is a number i such that i 2 = −1.
168) A specification for imaginary types is in informative annex G.

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7.3.2 Conventions
1

Values are interpreted as radians, not degrees. An implementation may set errno but is
not required to.

7.3.3 Branch cuts
1

Some of the functions below have branch cuts, across which the function is
discontinuous. For implementations with a signed zero (including all IEC 60559
implementations) that follow the specifications of annex G, the sign of zero distinguishes
one side of a cut from another so the function is continuous (except for format
limitations) as the cut is approached from either side. For example, for the square root
function, which has a branch cut along the negative real axis, the top of the cut, withimaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, withimaginary part −0, maps to the negative imaginary axis.

2

Implementations that do not support a signed zero (see annex F) cannot distinguish thesides of branch cuts. These implementations shall map a cut so the function is continuous
as the cut is approached coming around the finite endpoint of the cut in a counterclockwise direction. (Branch cuts for the functions specified here have just one finite
endpoint.) For example, for the square root function, coming counter clockwise aroundthe finite endpoint of the cut along the negative real axis approaches the cut from above,so the cut maps to the positive imaginary axis.

7.3.4 The CX_LIMITED_RANGE pragma
Synopsis1#include <complex.h>#pragma STDC CX_LIMITED_RANGE on-off-switch
Description

2

The usual mathematical formulas for complex multiply, divide, and absolute value areproblematic because of their treatment of infinities and because of undue overflow andunderflow. The CX_LIMITED_RANGE pragma can be used to inform theimplementation that (where the state is ‘‘on’’) the usual mathematical formulas are
acceptable.169) The pragma can occur either outside external declarations or preceding all
explicit declarations and statements inside a compound statement. When outside external169) The purpose of the pragma is to allow the implementation to use the formulas:(x + iy) × (u + iv) = (xu − yv) + i(yu + xv)(x + iy) / (u + iv) = [(xu + yv) + i(yu − xv)]/(u2 + v 2 )| x + iy | = √x 2 + y2
where the programmer can determine they are safe.

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declarations, the pragma takes effect from its occurrence until another
CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
When inside a compound statement, the pragma takes effect from its occurrence until
another CX_LIMITED_RANGE pragma is encountered (including within a nested
compound statement), or until the end of the compound statement; at the end of acompound statement the state for the pragma is restored to its condition just before thecompound statement. If this pragma is used in any other context, the behavior isundefined. The default state for the pragma is ‘‘off’’.

7.3.5 Trigonometric functions
7.3.5.1 The cacos functions
Synopsis1#include <complex.h>double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);
Description

2

The cacos functions compute the complex arc cosine of z, with branch cuts outside theinterval [−1, +1] along the real axis.
Returns3

The cacos functions return the complex arc cosine value, in the range of a strip
mathematically unbounded along the imaginary axis and in the interval [0, π ] along thereal axis.

7.3.5.2 The casin functions
Synopsis1#include <complex.h>double complex casin(double complex z);
float complex casinf(float complex z);
long double complex casinl(long double complex z);
Description

2

The casin functions compute the complex arc sine of z, with branch cuts outside theinterval [−1, +1] along the real axis.
Returns3

The casin functions return the complex arc sine value, in the range of a strip
mathematically unbounded along the imaginary axis and in the interval [−π /2, +π /2]along the real axis.
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7.3.5.3 The catan functions
Synopsis1#include <complex.h>double complex catan(double complex z);
float complex catanf(float complex z);
long double complex catanl(long double complex z);
Description

2

The catan functions compute the complex arc tangent of z, with branch cuts outside theinterval [−i, +i] along the imaginary axis.
Returns3

The catan functions return the complex arc tangent value, in the range of a strip
mathematically unbounded along the imaginary axis and in the interval [−π /2, +π /2]along the real axis.

7.3.5.4 The ccos functions
Synopsis1#include <complex.h>double complex ccos(double complex z);
float complex ccosf(float complex z);
long double complex ccosl(long double complex z);
Description

2

The ccos functions compute the complex cosine of z.
Returns3

The ccos functions return the complex cosine value.

7.3.5.5 The csin functions
Synopsis1#include <complex.h>double complex csin(double complex z);
float complex csinf(float complex z);
long double complex csinl(long double complex z);
Description

2

The csin functions compute the complex sine of z.
Returns3

The csin functions return the complex sine value.
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7.3.5.6 The ctan functions
Synopsis1#include <complex.h>double complex ctan(double complex z);
float complex ctanf(float complex z);
long double complex ctanl(long double complex z);
Description

2

The ctan functions compute the complex tangent of z.
Returns3

The ctan functions return the complex tangent value.

7.3.6 Hyperbolic functions
7.3.6.1 The cacosh functions
Synopsis1#include <complex.h>double complex cacosh(double complex z);
float complex cacoshf(float complex z);
long double complex cacoshl(long double complex z);
Description

2

The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
cut at values less than 1 along the real axis.
Returns3

The cacosh functions return the complex arc hyperbolic cosine value, in the range of ahalf-strip of non-negative values along the real axis and in the interval [−iπ , +iπ ] along
the imaginary axis.

7.3.6.2 The casinh functions
Synopsis1#include <complex.h>double complex casinh(double complex z);
float complex casinhf(float complex z);
long double complex casinhl(long double complex z);
Description

2

The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
outside the interval [−i, +i] along the imaginary axis.
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Returns3

The casinh functions return the complex arc hyperbolic sine value, in the range of a
strip mathematically unbounded along the real axis and in the interval [−iπ /2, +iπ /2]along the imaginary axis.

7.3.6.3 The catanh functions
Synopsis1#include <complex.h>double complex catanh(double complex z);
float complex catanhf(float complex z);
long double complex catanhl(long double complex z);
Description

2

The catanh functions compute the complex arc hyperbolic tangent of z, with branchcuts outside the interval [−1, +1] along the real axis.
Returns3

The catanh functions return the complex arc hyperbolic tangent value, in the range of a
strip mathematically unbounded along the real axis and in the interval [−iπ /2, +iπ /2]along the imaginary axis.

7.3.6.4 The ccosh functions
Synopsis1#include <complex.h>double complex ccosh(double complex z);
float complex ccoshf(float complex z);
long double complex ccoshl(long double complex z);
Description

2

The ccosh functions compute the complex hyperbolic cosine of z.
Returns3

The ccosh functions return the complex hyperbolic cosine value.

7.3.6.5 The csinh functions
Synopsis1#include <complex.h>double complex csinh(double complex z);
float complex csinhf(float complex z);
long double complex csinhl(long double complex z);§7.3.6.5

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Description
2

The csinh functions compute the complex hyperbolic sine of z.
Returns3

The csinh functions return the complex hyperbolic sine value.

7.3.6.6 The ctanh functions
Synopsis1#include <complex.h>double complex ctanh(double complex z);
float complex ctanhf(float complex z);
long double complex ctanhl(long double complex z);
Description

2

The ctanh functions compute the complex hyperbolic tangent of z.
Returns3

The ctanh functions return the complex hyperbolic tangent value.

7.3.7 Exponential and logarithmic functions
7.3.7.1 The cexp functions
Synopsis1#include <complex.h>double complex cexp(double complex z);
float complex cexpf(float complex z);
long double complex cexpl(long double complex z);
Description

2

The cexp functions compute the complex base-e exponential of z.
Returns3

The cexp functions return the complex base-e exponential value.

7.3.7.2 The clog functions
Synopsis1#include <complex.h>double complex clog(double complex z);
float complex clogf(float complex z);
long double complex clogl(long double complex z);

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Description
2

The clog functions compute the complex natural (base-e) logarithm of z, with a branch
cut along the negative real axis.
Returns3

The clog functions return the complex natural logarithm value, in the range of a strip
mathematically unbounded along the real axis and in the interval [−iπ , +iπ ] along theimaginary axis.

7.3.8 Power and absolute-value functions
7.3.8.1 The cabs functions
Synopsis1#include <complex.h>double cabs(double complex z);
float cabsf(float complex z);
long double cabsl(long double complex z);
Description

2

The cabs functions compute the complex absolute value (also called norm, modulus, ormagnitude) of z.
Returns3

The cabs functions return the complex absolute value.

7.3.8.2 The cpow functions
Synopsis1#include <complex.h>double complex cpow(double complex x, double complex y);
float complex cpowf(float complex x, float complex y);long double complex cpowl(long double complex x,
long double complex y);
Description

2

The cpow functions compute the complex power function xy , with a branch cut for the
first parameter along the negative real axis.
Returns3

The cpow functions return the complex power function value.

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7.3.8.3 The csqrt functions
Synopsis1#include <complex.h>double complex csqrt(double complex z);
float complex csqrtf(float complex z);
long double complex csqrtl(long double complex z);
Description

2

The csqrt functions compute the complex square root of z, with a branch cut along thenegative real axis.
Returns3

The csqrt functions return the complex square root value, in the range of the right halfplane (including the imaginary axis).

7.3.9 Manipulation functions
7.3.9.1 The carg functions
Synopsis1#include <complex.h>double carg(double complex z);
float cargf(float complex z);
long double cargl(long double complex z);
Description

2

The carg functions compute the argument (also called phase angle) of z, with a branch
cut along the negative real axis.
Returns3

The carg functions return the value of the argument in the interval [−π , +π ].

7.3.9.2 The cimag functions
Synopsis1#include <complex.h>double cimag(double complex z);
float cimagf(float complex z);
long double cimagl(long double complex z);

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Description
2

The cimag functions compute the imaginary part of z.170)
Returns3

The cimag functions return the imaginary part value (as a real).

7.3.9.3 The conj functions
Synopsis1#include <complex.h>double complex conj(double complex z);
float complex conjf(float complex z);
long double complex conjl(long double complex z);
Description

2

The conj functions compute the complex conjugate of z, by reversing the sign of its
imaginary part.
Returns3

The conj functions return the complex conjugate value.

7.3.9.4 The cproj functions
Synopsis1#include <complex.h>double complex cproj(double complex z);
float complex cprojf(float complex z);
long double complex cprojl(long double complex z);
Description

2

The cproj functions compute a projection of z onto the Riemann sphere: z projects toz except that all complex infinities (even those with one infinite part and one NaN part)project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
equivalent to
INFINITY + I * copysign(0.0, cimag(z))
Returns3

The cproj functions return the value of the projection onto the Riemann sphere.

170) For a variable z of complex type, z == creal(z) + cimag(z)*I.

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7.3.9.5 The creal functions
Synopsis1#include <complex.h>double creal(double complex z);
float crealf(float complex z);
long double creall(long double complex z);
Description

2

The creal functions compute the real part of z.171)
Returns3

The creal functions return the real part value.

171) For a variable z of complex type, z == creal(z) + cimag(z)*I.

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7.4 Character handling <ctype.h>
1

The header <ctype.h> declares several functions useful for classifying and mapping
characters.172) In all cases the argument is an int, the value of which shall be
representable as an unsigned char or shall equal the value of the macro EOF. If theargument has any other value, the behavior is undefined.

2

The behavior of these functions is affected by the current locale. Those functions thathave locale-specific aspects only when not in the "C" locale are noted below.

3

The term printing character refers to a member of a locale-specific set of characters, eachof which occupies one printing position on a display device; the term control character
refers to a member of a locale-specific set of characters that are not printing
characters.173) All letters and digits are printing characters.
Forward references: EOF (7.19.1), localization (7.11).

7.4.1 Character classification functions
1

The functions in this subclause return nonzero (true) if and only if the value of theargument c conforms to that in the description of the function.

7.4.1.1 The isalnum function
Synopsis1#include <ctype.h>
int isalnum(int c);
Description

2

The isalnum function tests for any character for which isalpha or isdigit is true.

7.4.1.2 The isalpha function
Synopsis1#include <ctype.h>
int isalpha(int c);
Description

2

The isalpha function tests for any character for which isupper or islower is true,or any character that is one of a locale-specific set of alphabetic characters for which

172) See ‘‘future library directions’’ (7.26.2).
173) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).

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none of iscntrl, isdigit, ispunct, or isspace is true.174) In the "C" locale,
isalpha returns true only for the characters for which isupper or islower is true.

7.4.1.3 The isblank function
Synopsis1#include <ctype.h>
int isblank(int c);
Description

2

The isblank function tests for any character that is a standard blank character or is oneof a locale-specific set of characters for which isspace is true and that is used toseparate words within a line of text. The standard blank characters are the following:
space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
for the standard blank characters.

7.4.1.4 The iscntrl function
Synopsis1#include <ctype.h>
int iscntrl(int c);
Description

2

The iscntrl function tests for any control character.

7.4.1.5 The isdigit function
Synopsis1#include <ctype.h>
int isdigit(int c);
Description

2

The isdigit function tests for any decimal-digit character (as defined in 5.2.1).

7.4.1.6 The isgraph function
Synopsis1#include <ctype.h>
int isgraph(int c);174) The functions islower and isupper test true or false separately for each of these additional
characters; all four combinations are possible.

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Description
2

The isgraph function tests for any printing character except space (' ').

7.4.1.7 The islower function
Synopsis1#include <ctype.h>
int islower(int c);
Description

2

The islower function tests for any character that is a lowercase letter or is one of a
locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
isspace is true. In the "C" locale, islower returns true only for the lowercase
letters (as defined in 5.2.1).

7.4.1.8 The isprint function
Synopsis1#include <ctype.h>
int isprint(int c);
Description

2

The isprint function tests for any printing character including space (' ').

7.4.1.9 The ispunct function
Synopsis1#include <ctype.h>
int ispunct(int c);
Description

2

The ispunct function tests for any printing character that is one of a locale-specific setof punctuation characters for which neither isspace nor isalnum is true. In the "C"
locale, ispunct returns true for every printing character for which neither isspace
nor isalnum is true.

7.4.1.10 The isspace function
Synopsis1#include <ctype.h>
int isspace(int c);
Description

2

The isspace function tests for any character that is a standard white-space character oris one of a locale-specific set of characters for which isalnum is false. The standard§7.4.1.10

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white-space characters are the following: space (' '), form feed ('\f'), new-line('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the"C" locale, isspace returns true only for the standard white-space characters.

7.4.1.11 The isupper function
Synopsis1#include <ctype.h>
int isupper(int c);
Description

2

The isupper function tests for any character that is an uppercase letter or is one of a
locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
isspace is true. In the "C" locale, isupper returns true only for the uppercase
letters (as defined in 5.2.1).

7.4.1.12 The isxdigit function
Synopsis1#include <ctype.h>
int isxdigit(int c);
Description

2

The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).

7.4.2 Character case mapping functions
7.4.2.1 The tolower function
Synopsis1#include <ctype.h>
int tolower(int c);
Description

2

The tolower function converts an uppercase letter to a corresponding lowercase letter.
Returns3

If the argument is a character for which isupper is true and there are one or morecorresponding characters, as specified by the current locale, for which islower is true,
the tolower function returns one of the corresponding characters (always the same one
for any given locale); otherwise, the argument is returned unchanged.

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7.4.2.2 The toupper function
Synopsis1#include <ctype.h>
int toupper(int c);
Description

2

The toupper function converts a lowercase letter to a corresponding uppercase letter.
Returns3

If the argument is a character for which islower is true and there are one or morecorresponding characters, as specified by the current locale, for which isupper is true,
the toupper function returns one of the corresponding characters (always the same one
for any given locale); otherwise, the argument is returned unchanged.

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7.5 Errors <errno.h>
1

The header <errno.h> defines several macros, all relating to the reporting of error
conditions.

2

The macros are
EDOM
EILSEQ
ERANGE
which expand to integer constant expressions with type int, distinct positive values, andwhich are suitable for use in #if preprocessing directives; anderrno
which expands to a modifiable lvalue175) that has type int, the value of which is set to a
positive error number by several library functions. It is unspecified whether errno is amacro or an identifier declared with external linkage. If a macro definition is suppressedin order to access an actual object, or a program defines an identifier with the name
errno, the behavior is undefined.

3

The value of errno is zero at program startup, but is never set to zero by any libraryfunction.176) The value of errno may be set to nonzero by a library function callwhether or not there is an error, provided the use of errno is not documented in thedescription of the function in this International Standard.

4Additional macro definitions, beginning with E and a digit or E and an uppercase
letter,177) may also be specified by the implementation.

175) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
resulting from a function call (for example, *errno()).
176) Thus, a program that uses errno for error checking should set it to zero before a library function call,then inspect it before a subsequent library function call. Of course, a library function can save thevalue of errno on entry and then set it to zero, as long as the original value is restored if errno’s
value is still zero just before the return.
177) See ‘‘future library directions’’ (7.26.3).

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7.6 Floating-point environment <fenv.h>
1

The header <fenv.h> declares two types and several macros and functions to provide
access to the floating-point environment. The floating-point environment refers
collectively to any floating-point status flags and control modes supported by the
implementation.178) A floating-point status flag is a system variable whose value is set(but never cleared) when a floating-point exception is raised, which occurs as a side effectof exceptional floating-point arithmetic to provide auxiliary information.179) A floatingpoint control mode is a system variable whose value may be set by the user to affect thesubsequent behavior of floating-point arithmetic.

2

Certain programming conventions support the intended model of use for the floatingpoint environment:180)— a function call does not alter its caller’s floating-point control modes, clear its caller’s
floating-point status flags, nor depend on the state of its caller’s floating-point status
flags unless the function is so documented;— a function call is assumed to require default floating-point control modes, unless its
documentation promises otherwise;— a function call is assumed to have the potential for raising floating-point exceptions,
unless its documentation promises otherwise.

3

The type
fenv_trepresents the entire floating-point environment.

4

The type
fexcept_t
represents the floating-point status flags collectively, including any status theimplementation associates with the flags.

178) This header is designed to support the floating-point exception status flags and directed-rounding
control modes required by IEC 60559, and other similar floating-point state information. Also it isdesigned to facilitate code portability among all systems.
179) A floating-point status flag is not an object and can be set more than once within an expression.
180) With these conventions, a programmer can safely assume default floating-point control modes (or be
unaware of them). The responsibilities associated with accessing the floating-point environment fallon the programmer or program that does so explicitly.

§7.6

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Each of the macros
FE_DIVBYZERO
FE_INEXACT
FE_INVALID
FE_OVERFLOW
FE_UNDERFLOW
is defined if and only if the implementation supports the floating-point exception bymeans of the functions in 7.6.2.181) Additional implementation-defined floating-point
exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also
be specified by the implementation. The defined macros expand to integer constant
expressions with values such that bitwise ORs of all combinations of the macros result indistinct values, and furthermore, bitwise ANDs of all combinations of the macros result inzero.182)

6

The macro
FE_ALL_EXCEPT
is simply the bitwise OR of all floating-point exception macros defined by the
implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.

7

Each of the macros
FE_DOWNWARD
FE_TONEAREST
FE_TOWARDZERO
FE_UPWARD
is defined if and only if the implementation supports getting and setting the represented
rounding direction by means of the fegetround and fesetround functions.
Additional implementation-defined rounding directions, with macro definitions beginningwith FE_ and an uppercase letter, may also be specified by the implementation. The
defined macros expand to integer constant expressions whose values are distinct
nonnegative values.183)

8

The macro181) The implementation supports an exception if there are circumstances where a call to at least one of thefunctions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not necessary for
all the functions to succeed all the time.

182) The macros should be distinct powers of two.
183) Even though the rounding direction macros may expand to constants corresponding to the values of
FLT_ROUNDS, they are not required to do so.

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FE_DFL_ENV
represents the default floating-point environment — the one installed at program startup— and has type ‘‘pointer to const-qualified fenv_t’’. It can be used as an argument to<fenv.h> functions that manage the floating-point environment.
9Additional implementation-defined environments, with macro definitions beginning with
FE_ and an uppercase letter, and having type ‘‘pointer to const-qualified fenv_t’’, mayalso be specified by the implementation.

7.6.1 The FENV_ACCESS pragma
Synopsis1#include <fenv.h>#pragma STDC FENV_ACCESS on-off-switch
Description

2

The FENV_ACCESS pragma provides a means to inform the implementation when aprogram might access the floating-point environment to test floating-point status flags or
run under non-default floating-point control modes.184) The pragma shall occur either
outside external declarations or preceding all explicit declarations and statements inside acompound statement. When outside external declarations, the pragma takes effect fromits occurrence until another FENV_ACCESS pragma is encountered, or until the end of
the translation unit. When inside a compound statement, the pragma takes effect from its
occurrence until another FENV_ACCESS pragma is encountered (including within anested compound statement), or until the end of the compound statement; at the end of acompound statement the state for the pragma is restored to its condition just before thecompound statement. If this pragma is used in any other context, the behavior isundefined. If part of a program tests floating-point status flags, sets floating-point control
modes, or runs under non-default mode settings, but was translated with the state for the
FENV_ACCESS pragma ‘‘off’’, the behavior is undefined. The default state (‘‘on’’ or‘‘off’’) for the pragma is implementation-defined. (When execution passes from a part ofthe program translated with FENV_ACCESS ‘‘off’’ to a part translated with
FENV_ACCESS ‘‘on’’, the state of the floating-point status flags is unspecified and thefloating-point control modes have their default settings.)

184) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flagtests and mode changes (e.g., global common subexpression elimination, code motion, and constantfolding). In general, if the state of FENV_ACCESS is ‘‘off’’, the translator can assume that default
modes are in effect and the flags are not tested.

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EXAMPLE#include <fenv.h>
void f(double x){#pragma STDC FENV_ACCESS ON
void g(double);
void h(double);/* ... */g(x + 1);h(x + 1);/* ... */}4

If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
x + 1 might depend on control modes set as a side effect of the call to function g, then the program shallcontain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.185)

7.6.2 Floating-point exceptions
1

The following functions provide access to the floating-point status flags.186) The int
input argument for the functions represents a subset of floating-point exceptions, and canbe zero or the bitwise OR of one or more floating-point exception macros, for example
FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of thesefunctions is undefined.

7.6.2.1 The feclearexcept function
Synopsis1#include <fenv.h>
int feclearexcept(int excepts);

Description
2

The feclearexcept function attempts to clear the supported floating-point exceptions
represented by its argument.

Returns

3

The feclearexcept function returns zero if the excepts argument is zero or if all
the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.

185) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is‘‘off’’, just one evaluation of x + 1 would suffice.
186) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
abstraction of flags that are either set or clear. An implementation may endow floating-point status
flags with more information — for example, the address of the code which first raised the floatingpoint exception; the functions fegetexceptflag and fesetexceptflag deal with the fullcontent of flags.

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7.6.2.2 The fegetexceptflag function
Synopsis1#include <fenv.h>
int fegetexceptflag(fexcept_t *flagp,
int excepts);

Description
2

The fegetexceptflag function attempts to store an implementation-defined
representation of the states of the floating-point status flags indicated by the argument
excepts in the object pointed to by the argument flagp.

Returns

3

The fegetexceptflag function returns zero if the representation was successfully
stored. Otherwise, it returns a nonzero value.

7.6.2.3 The feraiseexcept function
Synopsis1#include <fenv.h>
int feraiseexcept(int excepts);

Description
2

The feraiseexcept function attempts to raise the supported floating-point exceptions
represented by its argument.187) The order in which these floating-point exceptions areraised is unspecified, except as stated in F.7.6. Whether the feraiseexcept function
additionally raises the ‘‘inexact’’ floating-point exception whenever it raises the‘‘overflow’’ or ‘‘underflow’’ floating-point exception is implementation-defined.

Returns

3

The feraiseexcept function returns zero if the excepts argument is zero or if all
the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.

187) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
Hence, enabled traps for floating-point exceptions raised by this function are taken. The specificationin F.7.6 is in the same spirit.

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7.6.2.4 The fesetexceptflag function
Synopsis1#include <fenv.h>
int fesetexceptflag(const fexcept_t *flagp,
int excepts);

Description
2

The fesetexceptflag function attempts to set the floating-point status flags
indicated by the argument excepts to the states stored in the object pointed to byflagp. The value of *flagp shall have been set by a previous call tofegetexceptflag whose second argument represented at least those floating-point
exceptions represented by the argument excepts. This function does not raise floatingpoint exceptions, but only sets the state of the flags.

Returns

3

The fesetexceptflag function returns zero if the excepts argument is zero or if
all the specified flags were successfully set to the appropriate state. Otherwise, it returns
a nonzero value.

7.6.2.5 The fetestexcept function
Synopsis1#include <fenv.h>
int fetestexcept(int excepts);
Description

2

The fetestexcept function determines which of a specified subset of the floatingpoint exception flags are currently set. The excepts argument specifies the floatingpoint status flags to be queried.188)
Returns

3

The fetestexcept function returns the value of the bitwise OR of the floating-point
exception macros corresponding to the currently set floating-point exceptions included in
excepts.

4

EXAMPLE

Call f if ‘‘invalid’’ is set, then g if ‘‘overflow’’ is set:

188) This mechanism allows testing several floating-point exceptions with just one function call.

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ISO/IEC 9899:TC3#include <fenv.h>/* ... */{#pragma STDC FENV_ACCESS ON
int set_excepts;
feclearexcept(FE_INVALID | FE_OVERFLOW);// maybe raise exceptions
set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
if (set_excepts & FE_INVALID) f();if (set_excepts & FE_OVERFLOW) g();/* ... */}7.6.3 Rounding
1

The fegetround and fesetround functions provide control of rounding direction
modes.

7.6.3.1 The fegetround function
Synopsis1#include <fenv.h>
int fegetround(void);
Description

2

The fegetround function gets the current rounding direction.
Returns

3

The fegetround function returns the value of the rounding direction macro
representing the current rounding direction or a negative value if there is no suchrounding direction macro or the current rounding direction is not determinable.

7.6.3.2 The fesetround function
Synopsis1#include <fenv.h>
int fesetround(int round);Description

2

The fesetround function establishes the rounding direction represented by its
argument round. If the argument is not equal to the value of a rounding direction macro,
the rounding direction is not changed.
Returns

3

The fesetround function returns zero if and only if the requested rounding direction
was established.

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EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting therounding direction fails.
#include <fenv.h>#include <assert.h>void f(int round_dir){#pragma STDC FENV_ACCESS ON
int save_round;
int setround_ok;
save_round = fegetround();setround_ok = fesetround(round_dir);
assert(setround_ok == 0);/* ... */fesetround(save_round);/* ... */}7.6.4 Environment
1

The functions in this section manage the floating-point environment — status flags andcontrol modes — as one entity.

7.6.4.1 The fegetenv function
Synopsis1#include <fenv.h>
int fegetenv(fenv_t *envp);

Description
2

The fegetenv function attempts to store the current floating-point environment in theobject pointed to by envp.

Returns

3

The fegetenv function returns zero if the environment was successfully stored.
Otherwise, it returns a nonzero value.

7.6.4.2 The feholdexcept function
Synopsis1#include <fenv.h>
int feholdexcept(fenv_t *envp);
Description

2

The feholdexcept function saves the current floating-point environment in the object
pointed to by envp, clears the floating-point status flags, and then installs a non-stop(continue on floating-point exceptions) mode, if available, for all floating-point
exceptions.189)
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Returns
3

The feholdexcept function returns zero if and only if non-stop floating-point
exception handling was successfully installed.

7.6.4.3 The fesetenv function
Synopsis1#include <fenv.h>
int fesetenv(const fenv_t *envp);

Description
2

The fesetenv function attempts to establish the floating-point environment represented
by the object pointed to by envp. The argument envp shall point to an object set by acall to fegetenv or feholdexcept, or equal a floating-point environment macro.
Note that fesetenv merely installs the state of the floating-point status flags
represented through its argument, and does not raise these floating-point exceptions.

Returns

3

The fesetenv function returns zero if the environment was successfully established.
Otherwise, it returns a nonzero value.

7.6.4.4 The feupdateenv function
Synopsis1#include <fenv.h>
int feupdateenv(const fenv_t *envp);

Description
2

The feupdateenv function attempts to save the currently raised floating-point
exceptions in its automatic storage, install the floating-point environment represented by
the object pointed to by envp, and then raise the saved floating-point exceptions. The
argument envp shall point to an object set by a call to feholdexcept or fegetenv,
or equal a floating-point environment macro.

Returns

3

The feupdateenv function returns zero if all the actions were successfully carried out.
Otherwise, it returns a nonzero value.

189) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
such systems, the feholdexcept function can be used in conjunction with the feupdateenv
function to write routines that hide spurious floating-point exceptions from their callers.

§7.6.4.4

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Hide spurious underflow floating-point exceptions:#include <fenv.h>double f(double x){#pragma STDC FENV_ACCESS ON
double result;fenv_t save_env;
if (feholdexcept(&save_env))
return /* indication of an environmental problem */;// compute resultif (/* test spurious underflow */)if (feclearexcept(FE_UNDERFLOW))
return /* indication of an environmental problem */;if (feupdateenv(&save_env))
return /* indication of an environmental problem */;return result;}

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7.7 Characteristics of floating types <float.h>
1

The header <float.h> defines several macros that expand to various limits andparameters of the standard floating-point types.

2

The macros, their meanings, and the constraints (or restrictions) on their values are listed
in 5.2.4.2.2.

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7.8 Format conversion of integer types <inttypes.h>
1

The header <inttypes.h> includes the header <stdint.h> and extends it withadditional facilities provided by hosted implementations.

2

It declares functions for manipulating greatest-width integers and converting numericcharacter strings to greatest-width integers, and it declares the type
imaxdiv_t
which is a structure type that is the type of the value returned by the imaxdiv function.
For each type declared in <stdint.h>, it defines corresponding macros for conversion
specifiers for use with the formatted input/output functions.190)
Forward references: integer types <stdint.h> (7.18), formatted input/output
functions (7.19.6), formatted wide character input/output functions (7.24.2).

7.8.1 Macros for format specifiers
1

Each of the following object-like macros191) expands to a character string literalcontaining a conversion specifier, possibly modified by a length modifier, suitable for use
within the format argument of a formatted input/output function when converting thecorresponding integer type. These macro names have the general form of PRI (character
string literals for the fprintf and fwprintf family) or SCN (character string literals
for the fscanf and fwscanf family),192) followed by the conversion specifier,followed by a name corresponding to a similar type name in 7.18.1. In these names, N
represents the width of the type as described in 7.18.1. For example, PRIdFAST32 canbe used in a format string to print the value of an integer of type int_fast32_t.

2

The fprintf macros for signed integers are:
PRIdN
PRIiN

PRIdLEASTNPRIiLEASTN

PRIdFASTN
PRIiFASTN

PRIdMAXPRIiMAX

PRIdPTR
PRIiPTR190) See ‘‘future library directions’’ (7.26.4).
191) C++ implementations should define these macros only when _ _STDC_FORMAT_MACROS is defined
before <inttypes.h> is included.
192) Separate macros are given for use with fprintf and fscanf functions because, in the general case,different format specifiers may be required for fprintf and fscanf, even when the type is the
same.

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3

PRIoLEASTNPRIuLEASTNPRIxLEASTNPRIXLEASTN

PRIoFASTN
PRIuFASTN
PRIxFASTN
PRIXFASTN

PRIoMAXPRIuMAXPRIxMAXPRIXMAX

PRIoPTR
PRIuPTR
PRIxPTRPRIXPTRSCNdMAXSCNiMAXSCNdPTR
SCNiPTRSCNoMAXSCNuMAXSCNxMAXSCNoPTRSCNuPTRSCNxPTRThe fscanf macros for signed integers are:
SCNdN
SCNiN

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The fprintf macros for unsigned integers are:
PRIoN
PRIuN
PRIxN
PRIXN

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SCNdLEASTNSCNiLEASTN

SCNdFASTN
SCNiFASTN

The fscanf macros for unsigned integers are:
SCNoN
SCNuN
SCNxN

SCNoLEASTNSCNuLEASTNSCNxLEASTN

SCNoFASTN
SCNuFASTN
SCNxFASTN

6

For each type that the implementation provides in <stdint.h>, the corresponding
fprintf macros shall be defined and the corresponding fscanf macros shall bedefined unless the implementation does not have a suitable fscanf length modifier forthe type.

7

EXAMPLE#include <inttypes.h>#include <wchar.h>
int main(void){
uintmax_t i = UINTMAX_MAX;// this type always exists
wprintf(L"The largest integer value is %020"
PRIxMAX "\n", i);return 0;}

7.8.2 Functions for greatest-width integer types
7.8.2.1 The imaxabs function
Synopsis1#include <inttypes.h>
intmax_t imaxabs(intmax_t j);
Description

2

The imaxabs function computes the absolute value of an integer j. If the result cannot
be represented, the behavior is undefined.193)

193) The absolute value of the most negative number cannot be represented in two’s complement.

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Returns3

The imaxabs function returns the absolute value.

7.8.2.2 The imaxdiv function
Synopsis1#include <inttypes.h>
imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
Description

2

The imaxdiv function computes numer / denom and numer % denom in a single
operation.
Returns3

The imaxdiv function returns a structure of type imaxdiv_t comprising both thequotient and the remainder. The structure shall contain (in either order) the members
quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
either part of the result cannot be represented, the behavior is undefined.

7.8.2.3 The strtoimax and strtoumax functions
Synopsis1#include <inttypes.h>
intmax_t strtoimax(const char * restrict nptr,
char ** restrict endptr, int base);uintmax_t strtoumax(const char * restrict nptr,
char ** restrict endptr, int base);
Description

2

The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
strtoul, and strtoull functions, except that the initial portion of the string isconverted to intmax_t and uintmax_t representation, respectively.
Returns

3

The strtoimax and strtoumax functions return the converted value, if any. If noconversion could be performed, zero is returned. If the correct value is outside the rangeof representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned(according to the return type and sign of the value, if any), and the value of the macro
ERANGE is stored in errno.
Forward references: the strtol, strtoll, strtoul, and strtoull functions(7.20.1.4).

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7.8.2.4 The wcstoimax and wcstoumax functions
Synopsis1#include <stddef.h>// for wchar_t#include <inttypes.h>
intmax_t wcstoimax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);uintmax_t wcstoumax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
Description

2

The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
wcstoul, and wcstoull functions except that the initial portion of the wide string isconverted to intmax_t and uintmax_t representation, respectively.
Returns

3

The wcstoimax function returns the converted value, if any. If no conversion could be
performed, zero is returned. If the correct value is outside the range of representablevalues, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to thereturn type and sign of the value, if any), and the value of the macro ERANGE is stored inerrno.
Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions(7.24.4.1.2).

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7.9 Alternative spellings <iso646.h>
1

The header <iso646.h> defines the following eleven macros (on the left) that expand
to the corresponding tokens (on the right):
andand_eqbitand
bitor
compl
not
not_eqor
or_eq
xor
xor_eq

202

&&
&=
&
|
~
!
!=
||
|=
^
^=

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7.10 Sizes of integer types <limits.h>
1

The header <limits.h> defines several macros that expand to various limits andparameters of the standard integer types.

2

The macros, their meanings, and the constraints (or restrictions) on their values are listed
in 5.2.4.2.1.

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7.11 Localization <locale.h>
1

The header <locale.h> declares two functions, one type, and defines several macros.

2

The type is
struct lconv
which contains members related to the formatting of numeric values. The structure shallcontain at least the following members, in any order. The semantics of the members andtheir normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall havethe values specified in the comments.
char *decimal_point;char *thousands_sep;char *grouping;char *mon_decimal_point;char *mon_thousands_sep;char *mon_grouping;char *positive_sign;
char *negative_sign;
char *currency_symbol;
char frac_digits;char p_cs_precedes;
char n_cs_precedes;
char p_sep_by_space;char n_sep_by_space;char p_sign_posn;
char n_sign_posn;
char *int_curr_symbol;
char int_frac_digits;char int_p_cs_precedes;
char int_n_cs_precedes;
char int_p_sep_by_space;char int_n_sep_by_space;char int_p_sign_posn;
char int_n_sign_posn;

204// "."
// ""
// ""
// ""
// ""
// ""
// ""
// ""
// ""
// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// ""// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX// CHAR_MAX

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The macros defined are NULL (described in 7.17); andLC_ALL
LC_COLLATE
LC_CTYPE
LC_MONETARYLC_NUMERIC
LC_TIME
which expand to integer constant expressions with distinct values, suitable for use as thefirst argument to the setlocale function.194) Additional macro definitions, beginningwith the characters LC_ and an uppercase letter,195) may also be specified by the
implementation.

7.11.1 Locale control
7.11.1.1 The setlocale function
Synopsis1#include <locale.h>char *setlocale(int category, const char *locale);Description

2

The setlocale function selects the appropriate portion of the program’s locale as
specified by the category and locale arguments. The setlocale function may be
used to change or query the program’s entire current locale or portions thereof. The value
LC_ALL for category names the program’s entire locale; the other values for
category name only a portion of the program’s locale. LC_COLLATE affects the
behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
the character handling functions196) and the multibyte and wide character functions.
LC_MONETARY affects the monetary formatting information returned by the
localeconv function. LC_NUMERIC affects the decimal-point character for theformatted input/output functions and the string conversion functions, as well as thenonmonetary formatting information returned by the localeconv function. LC_TIME
affects the behavior of the strftime and wcsftime functions.

3

A value of "C" for locale specifies the minimal environment for C translation; a valueof "" for locale specifies the locale-specific native environment. Other
implementation-defined strings may be passed as the second argument to setlocale.
194) ISO/IEC 9945−2 specifies locale and charmap formats that may be used to specify locales for C.
195) See ‘‘future library directions’’ (7.26.5).
196) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit andisxdigit.

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At program startup, the equivalent of
setlocale(LC_ALL, "C");is executed.

5

The implementation shall behave as if no library function calls the setlocale function.
Returns6

If a pointer to a string is given for locale and the selection can be honored, thesetlocale function returns a pointer to the string associated with the specified
category for the new locale. If the selection cannot be honored, the setlocale
function returns a null pointer and the program’s locale is not changed.

7

A null pointer for locale causes the setlocale function to return a pointer to thestring associated with the category for the program’s current locale; the program’s
locale is not changed.197)

8

The pointer to string returned by the setlocale function is such that a subsequent callwith that string value and its associated category will restore that part of the program’s
locale. The string pointed to shall not be modified by the program, but may beoverwritten by a subsequent call to the setlocale function.
Forward references: formatted input/output functions (7.19.6), multibyte/wide
character conversion functions (7.20.7), multibyte/wide string conversion functions(7.20.8), numeric conversion functions (7.20.1), the strcoll function (7.21.4.3), thestrftime function (7.23.3.5), the strxfrm function (7.21.4.5).

7.11.2 Numeric formatting convention inquiry
7.11.2.1 The localeconv function
Synopsis1#include <locale.h>struct lconv *localeconv(void);
Description

2

The localeconv function sets the components of an object with type struct lconv
with values appropriate for the formatting of numeric quantities (monetary and otherwise)
according to the rules of the current locale.

3

The members of the structure with type char * are pointers to strings, any of which(except decimal_point) can point to "", to indicate that the value is not available inthe current locale or is of zero length. Apart from grouping and mon_grouping, the197) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
locale when category has the value LC_ALL.

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strings shall start and end in the initial shift state. The members with type char are
nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is notavailable in the current locale. The members include the following:char *decimal_point
The decimal-point character used to format nonmonetary quantities.
char *thousands_sep
The character used to separate groups of digits before the decimal-point
character in formatted nonmonetary quantities.
char *groupingA string whose elements indicate the size of each group of digits informatted nonmonetary quantities.
char *mon_decimal_point
The decimal-point used to format monetary quantities.
char *mon_thousands_sep
The separator for groups of digits before the decimal-point in formatted
monetary quantities.
char *mon_groupingA string whose elements indicate the size of each group of digits informatted monetary quantities.
char *positive_sign
The string used to indicate a nonnegative-valued formatted monetary
quantity.
char *negative_sign
The string used to indicate a negative-valued formatted monetary quantity.
char *currency_symbol
The local currency symbol applicable to the current locale.
char frac_digits
The number of fractional digits (those after the decimal-point) to be
displayed in a locally formatted monetary quantity.
char p_cs_precedes
Set to 1 or 0 if the currency_symbol respectively precedes or
succeeds the value for a nonnegative locally formatted monetary quantity.
char n_cs_precedes
Set to 1 or 0 if the currency_symbol respectively precedes or
succeeds the value for a negative locally formatted monetary quantity.

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char p_sep_by_space
Set to a value indicating the separation of the currency_symbol, thesign string, and the value for a nonnegative locally formatted monetary
quantity.
char n_sep_by_space
Set to a value indicating the separation of the currency_symbol, thesign string, and the value for a negative locally formatted monetary
quantity.
char p_sign_posn
Set to a value indicating the positioning of the positive_sign for anonnegative locally formatted monetary quantity.
char n_sign_posn
Set to a value indicating the positioning of the negative_sign for anegative locally formatted monetary quantity.
char *int_curr_symbol
The international currency symbol applicable to the current locale. The
first three characters contain the alphabetic international currency symbolin accordance with those specified in ISO 4217. The fourth character(immediately preceding the null character) is the character used to separate
the international currency symbol from the monetary quantity.
char int_frac_digits
The number of fractional digits (those after the decimal-point) to be
displayed in an internationally formatted monetary quantity.
char int_p_cs_precedes
Set to 1 or 0 if the int_curr_symbol respectively precedes or
succeeds the value for a nonnegative internationally formatted monetary
quantity.

char int_n_cs_precedes
Set to 1 or 0 if the int_curr_symbol respectively precedes or
succeeds the value for a negative internationally formatted monetary
quantity.

char int_p_sep_by_space
Set to a value indicating the separation of the int_curr_symbol, thesign string, and the value for a nonnegative internationally formatted
monetary quantity.

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char int_n_sep_by_space
Set to a value indicating the separation of the int_curr_symbol, thesign string, and the value for a negative internationally formatted monetary
quantity.

char int_p_sign_posn
Set to a value indicating the positioning of the positive_sign for anonnegative internationally formatted monetary quantity.
char int_n_sign_posn
Set to a value indicating the positioning of the negative_sign for anegative internationally formatted monetary quantity.
4

5

The elements of grouping and mon_grouping are interpreted according to thefollowing:
CHAR_MAXNo further grouping is to be performed.

0

The previous element is to be repeatedly used for the remainder of thedigits.

other

The integer value is the number of digits that compose the current group.
The next element is examined to determine the size of the next group ofdigits before the current group.

The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,and int_n_sep_by_space are interpreted according to the following:0

No space separates the currency symbol and value.

1

If the currency symbol and sign string are adjacent, a space separates them from thevalue; otherwise, a space separates the currency symbol from the value.

If the currency symbol and sign string are adjacent, a space separates them;otherwise, a space separates the sign string from the value.
For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
int_curr_symbol is used instead of a space.
2

6

The values of p_sign_posn, n_sign_posn, int_p_sign_posn,
int_n_sign_posn are interpreted according to the following:0

Parentheses surround the quantity and currency symbol.

1

The sign string precedes the quantity and currency symbol.

2

The sign string succeeds the quantity and currency symbol.

3

The sign string immediately precedes the currency symbol.

4

The sign string immediately succeeds the currency symbol.

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The implementation shall behave as if no library function calls the localeconv
function.
Returns

8

The localeconv function returns a pointer to the filled-in object. The structure
pointed to by the return value shall not be modified by the program, but may beoverwritten by a subsequent call to the localeconv function. In addition, calls to thesetlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
overwrite the contents of the structure.

9

EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
monetary quantities.

Local format

10International format

Country

Positive

Negative

Positive

Negative

Country1
Country2
Country3
Country4

1.234,56 mk
L.1.234
ƒ 1.234,56
SFrs.1,234.56-1.234,56 mk-L.1.234
ƒ -1.234,56
SFrs.1,234.56C

FIM 1.234,56
ITL 1.234
NLG 1.234,56
CHF 1,234.56

FIM -1.234,56-ITL 1.234
NLG -1.234,56
CHF 1,234.56C

For these four countries, the respective values for the monetary members of the structure returned by
localeconv could be:

mon_decimal_point
mon_thousands_sep
mon_grouping
positive_sign
negative_sign
currency_symbol
frac_digits
p_cs_precedes
n_cs_precedes
p_sep_by_space
n_sep_by_space
p_sign_posn
n_sign_posn
int_curr_symbol
int_frac_digits
int_p_cs_precedes
int_n_cs_precedes
int_p_sep_by_space
int_n_sep_by_space
int_p_sign_posn
int_n_sign_posn

210Country1

Country2

Country3

Country4

","
"."
"\3"
""
"-"
"mk"
2
0
0
1
1
1
1
"FIM "
2
1
1
1
2
1
4

""
"."
"\3"
""
"-"
"L."
0
1
1
0
0
1
1
"ITL "
0
1
1
1
1
1
1

","
"."
"\3"
""
"-"
"\u0192"
2
1
1
1
2
1
4
"NLG "
2
1
1
1
2
1
4

"."
","
"\3"
""
"C"
"SFrs."
2
1
1
0
0
1
2
"CHF "
2
1
1
1
1
1
2

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EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
affect the formatted value.
p_sep_by_space

p_cs_precedes

p_sign_posn

01§7.11.2.1

0

1

2

0
1
2
3
4

(1.25$)+1.25$
1.25$+
1.25+$
1.25$+(1.25 $)
+1.25 $
1.25 $+
1.25 +$
1.25 $+(1.25$)+ 1.25$
1.25$ +
1.25+ $
1.25$ +

0
1
2
3
4($1.25)+$1.25$1.25++$1.25$+1.25($ 1.25)+$ 1.25$ 1.25++$ 1.25$+ 1.25($1.25)+ $1.25$1.25 +
+ $1.25$ +1.25

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7.12 Mathematics <math.h>
1

The header <math.h> declares two types and many mathematical functions and defines
several macros. Most synopses specify a family of functions consisting of a principal
function with one or more double parameters, a double return value, or both; andother functions with the same name but with f and l suffixes, which are corresponding
functions with float and long double parameters, return values, or both.198)
Integer arithmetic functions and conversion functions are discussed later.

2

The types
float_tdouble_t
are floating types at least as wide as float and double, respectively, and such that
double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
float_t and double_t are float and double, respectively; if
FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
2, they are both long double; and for other values of FLT_EVAL_METHOD, they areotherwise implementation-defined.199)

3

The macro
HUGE_VAL
expands to a positive double constant expression, not necessarily representable as afloat. The macros
HUGE_VALF
HUGE_VALL
are respectively float and long double analogs of HUGE_VAL.200)

4The macro
INFINITY
expands to a constant expression of type float representing positive or unsigned
infinity, if available; else to a positive constant of type float that overflows at198) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
and return values in wider format than the synopsis prototype indicates.
199) The types float_t and double_t are intended to be the implementation’s most efficient types atleast as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, thetype float_t is the narrowest type used by the implementation to evaluate floating expressions.
200) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
supports infinities.

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translation time.201)
5The macroNAN
is defined if and only if the implementation supports quiet NaNs for the float type. It
expands to a constant expression of type float representing a quiet NaN.

6

The number classification macros

FP_INFINITE
FP_NANFP_NORMAL
FP_SUBNORMAL
FP_ZEROrepresent the mutually exclusive kinds of floating-point values. They expand to integer
constant expressions with distinct values. Additional implementation-defined floatingpoint classifications, with macro definitions beginning with FP_ and an uppercase letter,
may also be specified by the implementation.

7

The macro
FP_FAST_FMA
is optionally defined. If defined, it indicates that the fma function generally executes
about as fast as, or faster than, a multiply and an add of double operands.202) The
macrosFP_FAST_FMAF
FP_FAST_FMAL
are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
these macros expand to the integer constant 1.

8

The macros
FP_ILOGB0
FP_ILOGBNAN
expand to integer constant expressions whose values are returned by ilogb(x) if x iszero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or-INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.
201) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
202) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
directly with a hardware multiply-add instruction. Software implementations are expected to be
substantially slower.

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The macros
MATH_ERRNO
MATH_ERREXCEPT
expand to the integer constants 1 and 2, respectively; the macro
math_errhandling
expands to an expression that has type int and the value MATH_ERRNO,
MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling isconstant for the duration of the program. It is unspecified whether
math_errhandling is a macro or an identifier with external linkage. If a macrodefinition is suppressed or a program defines an identifier with the namemath_errhandling, the behavior is undefined.
If the expression
math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in<fenv.h>.

7.12.1 Treatment of error conditions
1

The behavior of each of the functions in <math.h> is specified for all representablevalues of its input arguments, except where stated otherwise. Each function shall execute
as if it were a single operation without generating any externally visible exceptional
conditions.

2

For all functions, a domain error occurs if an input argument is outside the domain overwhich the mathematical function is defined. The description of each function lists any
required domain errors; an implementation may define additional domain errors, provided
that such errors are consistent with the mathematical definition of the function.203) On adomain error, the function returns an implementation-defined value; if the integer
expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
errno acquires the value EDOM; if the integer expression math_errhandling &MATH_ERREXCEPT is nonzero, the ‘‘invalid’’ floating-point exception is raised.

3

Similarly, a range error occurs if the mathematical result of the function cannot be
represented in an object of the specified type, due to extreme magnitude.

4

A floating result overflows if the magnitude of the mathematical result is finite but solarge that the mathematical result cannot be represented without extraordinary roundoff
error in an object of the specified type. If a floating result overflows and default rounding
is in effect, or if the mathematical result is an exact infinity from finite arguments (forexample log(0.0)), then the function returns the value of the macro HUGE_VAL,203) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
error if the mathematical domain of the function does not include the infinity.

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HUGE_VALF, or HUGE_VALL according to the return type, with the same sign as thecorrect value of the function; if the integer expression math_errhandling &MATH_ERRNO is nonzero, the integer expression errno acquires the value ERANGE; if
the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the‘‘divide-by-zero’’ floating-point exception is raised if the mathematical result is an exact
infinity and the ‘‘overflow’’ floating-point exception is raised otherwise.
5

The result underflows if the magnitude of the mathematical result is so small that themathematical result cannot be represented, without extraordinary roundoff error, in an
object of the specified type.204) If the result underflows, the function returns animplementation-defined value whose magnitude is no greater than the smallest
normalized positive number in the specified type; if the integer expression
math_errhandling & MATH_ERRNO is nonzero, whether errno acquires thevalue
ERANGEisimplementation-defined;
iftheinteger
expression
math_errhandling & MATH_ERREXCEPT is nonzero, whether the ‘‘underflow’’floating-point exception is raised is implementation-defined.

7.12.2 The FP_CONTRACT pragma
Synopsis1#include <math.h>#pragma STDC FP_CONTRACT on-off-switch
Description

2

The FP_CONTRACT pragma can be used to allow (if the state is ‘‘on’’) or disallow (if thestate is ‘‘off’’) the implementation to contract expressions (6.5). Each pragma can occur
either outside external declarations or preceding all explicit declarations and statements
inside a compound statement. When outside external declarations, the pragma takes
effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
the end of the translation unit. When inside a compound statement, the pragma takes
effect from its occurrence until another FP_CONTRACT pragma is encountered(including within a nested compound statement), or until the end of the compoundstatement; at the end of a compound statement the state for the pragma is restored to its
condition just before the compound statement. If this pragma is used in any othercontext, the behavior is undefined. The default state (‘‘on’’ or ‘‘off’’) for the pragma is
implementation-defined.

204) The term underflow here is intended to encompass both ‘‘gradual underflow’’ as in IEC 60559 andalso ‘‘flush-to-zero’’ underflow.

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7.12.3 Classification macros
1

In the synopses in this subclause, real-floating indicates that the argument shall be an
expression of real floating type.

7.12.3.1 The fpclassify macro
Synopsis1#include <math.h>int fpclassify(real-floating x);
Description

2

The fpclassify macro classifies its argument value as NaN, infinite, normal,
subnormal, zero, or into another implementation-defined category. First, an argument
represented in a format wider than its semantic type is converted to its semantic type.
Then classification is based on the type of the argument.205)
Returns

3

The fpclassify macro returns the value of the number classification macro
appropriate to the value of its argument.

4

EXAMPLEThe fpclassify macro might be implemented in terms of ordinary functions as#define fpclassify(x) \((sizeof (x) == sizeof (float)) ? _ _fpclassifyf(x) : \(sizeof (x) == sizeof (double)) ? _ _fpclassifyd(x) : \_ _fpclassifyl(x))

7.12.3.2 The isfinite macro
Synopsis1#include <math.h>
int isfinite(real-floating x);
Description

2

The isfinite macro determines whether its argument has a finite value (zero,subnormal, or normal, and not infinite or NaN). First, an argument represented in aformat wider than its semantic type is converted to its semantic type. Then determination
is based on the type of the argument.

205) Since an expression can be evaluated with more range and precision than its type has, it is important toknow the type that classification is based on. For example, a normal long double value might
become subnormal when converted to double, and zero when converted to float.

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Returns3

The isfinite macro returns a nonzero value if and only if its argument has a finite
value.

7.12.3.3 The isinf macro
Synopsis1#include <math.h>
int isinf(real-floating x);
Description

2

The isinf macro determines whether its argument value is an infinity (positive or
negative). First, an argument represented in a format wider than its semantic type isconverted to its semantic type. Then determination is based on the type of the argument.
Returns3

The isinf macro returns a nonzero value if and only if its argument has an infinite
value.

7.12.3.4 The isnan macro
Synopsis1#include <math.h>
int isnan(real-floating x);
Description

2

The isnan macro determines whether its argument value is a NaN. First, an argument
represented in a format wider than its semantic type is converted to its semantic type.
Then determination is based on the type of the argument.206)
Returns3

The isnan macro returns a nonzero value if and only if its argument has a NaN value.

7.12.3.5 The isnormal macro
Synopsis1#include <math.h>
int isnormal(real-floating x);206) For the isnan macro, the type for determination does not matter unless the implementation supports
NaNs in the evaluation type but not in the semantic type.

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Description
2

The isnormal macro determines whether its argument value is normal (neither zero,subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
semantic type is converted to its semantic type. Then determination is based on the typeof the argument.
Returns3

The isnormal macro returns a nonzero value if and only if its argument has a normal
value.

7.12.3.6 The signbit macro
Synopsis1#include <math.h>int signbit(real-floating x);
Description

2

The signbit macro determines whether the sign of its argument value is negative.207)
Returns

3

The signbit macro returns a nonzero value if and only if the sign of its argument value
is negative.

7.12.4 Trigonometric functions
7.12.4.1 The acos functions
Synopsis1#include <math.h>double acos(double x);
float acosf(float x);
long double acosl(long double x);
Description

2

The acos functions compute the principal value of the arc cosine of x. A domain error
occurs for arguments not in the interval [−1, +1].
Returns3

The acos functions return arccos x in the interval [0, π ] radians.

207) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero isunsigned, it is treated as positive.

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7.12.4.2 The asin functions
Synopsis1#include <math.h>double asin(double x);
float asinf(float x);
long double asinl(long double x);
Description

2

The asin functions compute the principal value of the arc sine of x. A domain error
occurs for arguments not in the interval [−1, +1].
Returns3

The asin functions return arcsin x in the interval [−π /2, +π /2] radians.

7.12.4.3 The atan functions
Synopsis1#include <math.h>double atan(double x);
float atanf(float x);
long double atanl(long double x);
Description

2

The atan functions compute the principal value of the arc tangent of x.
Returns3

The atan functions return arctan x in the interval [−π /2, +π /2] radians.

7.12.4.4 The atan2 functions
Synopsis1#include <math.h>double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
Description

2

The atan2 functions compute the value of the arc tangent of y/x, using the signs of botharguments to determine the quadrant of the return value. A domain error may occur if
both arguments are zero.
Returns3

The atan2 functions return arctan y/x in the interval [−π , +π ] radians.
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7.12.4.5 The cos functions
Synopsis1#include <math.h>double cos(double x);
float cosf(float x);
long double cosl(long double x);
Description

2

The cos functions compute the cosine of x (measured in radians).
Returns3

The cos functions return cos x.

7.12.4.6 The sin functions
Synopsis1#include <math.h>double sin(double x);
float sinf(float x);
long double sinl(long double x);
Description

2

The sin functions compute the sine of x (measured in radians).
Returns

3

The sin functions return sin x.

7.12.4.7 The tan functions
Synopsis1#include <math.h>double tan(double x);
float tanf(float x);
long double tanl(long double x);
Description

2

The tan functions return the tangent of x (measured in radians).
Returns

3

The tan functions return tan x.

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7.12.5 Hyperbolic functions
7.12.5.1 The acosh functions
Synopsis1#include <math.h>double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
Description

2

The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
error occurs for arguments less than 1.
Returns3

The acosh functions return arcosh x in the interval [0, +∞].

7.12.5.2 The asinh functions
Synopsis1#include <math.h>double asinh(double x);
float asinhf(float x);
long double asinhl(long double x);
Description

2

The asinh functions compute the arc hyperbolic sine of x.
Returns3

The asinh functions return arsinh x.

7.12.5.3 The atanh functions
Synopsis1#include <math.h>double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
Description

2

The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
for arguments not in the interval [−1, +1]. A range error may occur if the argument
equals −1 or +1.

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Returns3

The atanh functions return artanh x.

7.12.5.4 The cosh functions
Synopsis1#include <math.h>double cosh(double x);
float coshf(float x);
long double coshl(long double x);
Description

2

The cosh functions compute the hyperbolic cosine of x. A range error occurs if themagnitude of x is too large.
Returns3

The cosh functions return cosh x.

7.12.5.5 The sinh functions
Synopsis1#include <math.h>double sinh(double x);
float sinhf(float x);
long double sinhl(long double x);
Description

2

The sinh functions compute the hyperbolic sine of x. A range error occurs if themagnitude of x is too large.
Returns

3

The sinh functions return sinh x.

7.12.5.6 The tanh functions
Synopsis1#include <math.h>double tanh(double x);
float tanhf(float x);
long double tanhl(long double x);
Description

2

The tanh functions compute the hyperbolic tangent of x.

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Returns
3

The tanh functions return tanh x.

7.12.6 Exponential and logarithmic functions
7.12.6.1 The exp functions
Synopsis1#include <math.h>double exp(double x);
float expf(float x);
long double expl(long double x);
Description

2

The exp functions compute the base-e exponential of x. A range error occurs if themagnitude of x is too large.
Returns3

The exp functions return ex .

7.12.6.2 The exp2 functions
Synopsis1#include <math.h>double exp2(double x);
float exp2f(float x);
long double exp2l(long double x);
Description

2

The exp2 functions compute the base-2 exponential of x. A range error occurs if themagnitude of x is too large.
Returns3

The exp2 functions return 2x .

7.12.6.3 The expm1 functions
Synopsis1#include <math.h>double expm1(double x);
float expm1f(float x);
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Description
2

The expm1 functions compute the base-e exponential of the argument, minus 1. A range
error occurs if x is too large.208)
Returns3

The expm1 functions return ex − 1.

7.12.6.4 The frexp functions
Synopsis1#include <math.h>double frexp(double value, int *exp);
float frexpf(float value, int *exp);
long double frexpl(long double value, int *exp);
Description

2

The frexp functions break a floating-point number into a normalized fraction and an
integral power of 2. They store the integer in the int object pointed to by exp.
Returns3

If value is not a floating-point number, the results are unspecified. Otherwise, thefrexp functions return the value x, such that x has a magnitude in the interval [1/2, 1) or
zero, and value equals x × 2*exp . If value is zero, both parts of the result are zero.

7.12.6.5 The ilogb functions
Synopsis1#include <math.h>
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
Description

2

The ilogb functions extract the exponent of x as a signed int value. If x is zero they
compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to callingthe corresponding logb function and casting the returned value to type int. A domain
error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
the range of the return type, the numeric result is unspecified.

208) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.

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Returns3

The ilogb functions return the exponent of x as a signed int value.
Forward references: the logb functions (7.12.6.11).

7.12.6.6 The ldexp functions
Synopsis1#include <math.h>double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long double x, int exp);
Description

2

The ldexp functions multiply a floating-point number by an integral power of 2. A
range error may occur.
Returns3

The ldexp functions return x × 2exp .

7.12.6.7 The log functions
Synopsis1#include <math.h>double log(double x);
float logf(float x);
long double logl(long double x);
Description

2

The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
the argument is negative. A range error may occur if the argument is zero.
Returns3

The log functions return loge x.

7.12.6.8 The log10 functions
Synopsis1#include <math.h>double log10(double x);
float log10f(float x);
long double log10l(long double x);§7.12.6.8

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Description
2

The log10 functions compute the base-10 (common) logarithm of x. A domain error
occurs if the argument is negative. A range error may occur if the argument is zero.
Returns3

The log10 functions return log10 x.

7.12.6.9 The log1p functions
Synopsis1#include <math.h>double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
Description

2

The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.209)
A domain error occurs if the argument is less than −1. A range error may occur if theargument equals −1.
Returns3

The log1p functions return loge (1 + x).

7.12.6.10 The log2 functions
Synopsis1#include <math.h>double log2(double x);
float log2f(float x);
long double log2l(long double x);
Description

2

The log2 functions compute the base-2 logarithm of x. A domain error occurs if theargument is less than zero. A range error may occur if the argument is zero.
Returns3

The log2 functions return log2 x.

209) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).

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7.12.6.11 The logb functions
Synopsis1#include <math.h>double logb(double x);
float logbf(float x);
long double logbl(long double x);
Description

2

The logb functions extract the exponent of x, as a signed integer value in floating-point
format. If x is subnormal it is treated as though it were normalized; thus, for positive
finite x,
1 ≤ x × FLT_RADIX−logb(x) < FLT_RADIX
A domain error or range error may occur if the argument is zero.

Returns3

The logb functions return the signed exponent of x.

7.12.6.12 The modf functions
Synopsis1#include <math.h>double modf(double value, double *iptr);
float modff(float value, float *iptr);
long double modfl(long double value, long double *iptr);
Description

2

The modf functions break the argument value into integral and fractional parts, each ofwhich has the same type and sign as the argument. They store the integral part (infloating-point format) in the object pointed to by iptr.
Returns3

The modf functions return the signed fractional part of value.

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7.12.6.13 The scalbn and scalbln functions
Synopsis1#include <math.h>double scalbn(double x, int n);
float scalbnf(float x, int n);long double scalbnl(long double x, int n);double scalbln(double x, long int n);
float scalblnf(float x, long int n);long double scalblnl(long double x, long int n);
Description

2

The scalbn and scalbln functions compute x × FLT_RADIXn efficiently, notnormally by computing FLT_RADIXn explicitly. A range error may occur.
Returns

3

The scalbn and scalbln functions return x × FLT_RADIXn .

7.12.7 Power and absolute-value functions
7.12.7.1 The cbrt functions
Synopsis1#include <math.h>double cbrt(double x);
float cbrtf(float x);
long double cbrtl(long double x);
Description

2

The cbrt functions compute the real cube root of x.
Returns3

The cbrt functions return x1/3 .

7.12.7.2 The fabs functions
Synopsis1#include <math.h>double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);
Description

2

The fabs functions compute the absolute value of a floating-point number x.
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Returns
3

The fabs functions return | x |.

7.12.7.3 The hypot functions
Synopsis1#include <math.h>double hypot(double x, double y);float hypotf(float x, float y);long double hypotl(long double x, long double y);
Description

2

The hypot functions compute the square root of the sum of the squares of x and y,without undue overflow or underflow. A range error may occur.

3

Returns

4

The hypot functions return √x2 + y2 .


7.12.7.4 The pow functions
Synopsis1#include <math.h>double pow(double x, double y);float powf(float x, float y);long double powl(long double x, long double y);
Description

2

The pow functions compute x raised to the power y. A domain error occurs if x is finite
and negative and y is finite and not an integer value. A range error may occur. A domain
error may occur if x is zero and y is zero. A domain error or range error may occur if x
is zero and y is less than zero.

Returns3

The pow functions return xy .

7.12.7.5 The sqrt functions
Synopsis1#include <math.h>double sqrt(double x);
float sqrtf(float x);
long double sqrtl(long double x);§7.12.7.5

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Description
2

The sqrt functions compute the nonnegative square root of x. A domain error occurs if
the argument is less than zero.
Returns

3

The sqrt functions return √x.

7.12.8 Error and gamma functions
7.12.8.1 The erf functions
Synopsis1#include <math.h>double erf(double x);
float erff(float x);
long double erfl(long double x);
Description

2

The erf functions compute the error function of x.
Returns3

The erf functions return erf x =

2

x

e dt.
π ∫
√
−t 2

0

7.12.8.2 The erfc functions
Synopsis1#include <math.h>double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);
Description

2

The erfc functions compute the complementary error function of x. A range error
occurs if x is too large.
Returns3

The erfc functions return erfc x = 1 − erf x =

230

2

∞

e dt.
π ∫
√

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7.12.8.3 The lgamma functions
Synopsis1#include <math.h>double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);
Description

2

The lgamma functions compute the natural logarithm of the absolute value of gamma of
x. A range error occurs if x is too large. A range error may occur if x is a negative
integer or zero.
Returns3

The lgamma functions return loge | Γ(x) |.

7.12.8.4 The tgamma functions
Synopsis1#include <math.h>double tgamma(double x);
float tgammaf(float x);
long double tgammal(long double x);
Description

2

The tgamma functions compute the gamma function of x. A domain error or range error
may occur if x is a negative integer or zero. A range error may occur if the magnitude ofx is too large or too small.

Returns
3

The tgamma functions return Γ(x).

7.12.9 Nearest integer functions
7.12.9.1 The ceil functions
Synopsis1#include <math.h>double ceil(double x);
float ceilf(float x);
long double ceill(long double x);
Description

2

The ceil functions compute the smallest integer value not less than x.
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Returns3

The ceil functions return x, expressed as a floating-point number.

7.12.9.2 The floor functions
Synopsis1#include <math.h>double floor(double x);
float floorf(float x);
long double floorl(long double x);
Description

2

The floor functions compute the largest integer value not greater than x.
Returns

3

The floor functions return x, expressed as a floating-point number.

7.12.9.3 The nearbyint functions
Synopsis1#include <math.h>double nearbyint(double x);
float nearbyintf(float x);
long double nearbyintl(long double x);
Description

2

The nearbyint functions round their argument to an integer value in floating-point
format, using the current rounding direction and without raising the ‘‘inexact’’ floatingpoint exception.
Returns

3

The nearbyint functions return the rounded integer value.

7.12.9.4 The rint functions
Synopsis1#include <math.h>double rint(double x);
float rintf(float x);
long double rintl(long double x);
Description

2

The rint functions differ from the nearbyint functions (7.12.9.3) only in that therint functions may raise the ‘‘inexact’’ floating-point exception if the result differs invalue from the argument.
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Returns3

The rint functions return the rounded integer value.

7.12.9.5 The lrint and llrint functions
Synopsis1#include <math.h>long int lrint(double x);
long int lrintf(float x);
long int lrintl(long double x);
long long int llrint(double x);
long long int llrintf(float x);
long long int llrintl(long double x);
Description

2

The lrint and llrint functions round their argument to the nearest integer value,rounding according to the current rounding direction. If the rounded value is outside therange of the return type, the numeric result is unspecified and a domain error or range
error may occur.
∗

Returns3

The lrint and llrint functions return the rounded integer value.

7.12.9.6 The round functions
Synopsis1#include <math.h>double round(double x);
float roundf(float x);
long double roundl(long double x);
Description

2

The round functions round their argument to the nearest integer value in floating-point
format, rounding halfway cases away from zero, regardless of the current rounding
direction.
Returns3

The round functions return the rounded integer value.

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7.12.9.7 The lround and llround functions
Synopsis1#include <math.h>long int lround(double x);
long int lroundf(float x);
long int lroundl(long double x);
long long int llround(double x);
long long int llroundf(float x);
long long int llroundl(long double x);
Description

2

The lround and llround functions round their argument to the nearest integer value,rounding halfway cases away from zero, regardless of the current rounding direction. If
the rounded value is outside the range of the return type, the numeric result is unspecified
and a domain error or range error may occur.

Returns3

The lround and llround functions return the rounded integer value.

7.12.9.8 The trunc functions
Synopsis1#include <math.h>double trunc(double x);
float truncf(float x);
long double truncl(long double x);
Description

2

The trunc functions round their argument to the integer value, in floating format,
nearest to but no larger in magnitude than the argument.
Returns

3

The trunc functions return the truncated integer value.

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7.12.10 Remainder functions
7.12.10.1 The fmod functions
Synopsis1#include <math.h>double fmod(double x, double y);float fmodf(float x, float y);long double fmodl(long double x, long double y);
Description

2

The fmod functions compute the floating-point remainder of x/y.
Returns

3

The fmod functions return the value x − ny, for some integer n such that, if y is nonzero,
the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
whether a domain error occurs or the fmod functions return zero is implementationdefined.

7.12.10.2 The remainder functions
Synopsis1#include <math.h>double remainder(double x, double y);float remainderf(float x, float y);long double remainderl(long double x, long double y);
Description

2

The remainder functions compute the remainder x REM y required by IEC 60559.210)
Returns3

The remainder functions return x REM y. If y is zero, whether a domain error occurs
or the functions return zero is implementation defined.

210) ‘‘When y ≠ 0, the remainder r = x REM y is defined regardless of the rounding mode by themathematical relation r = x − ny, where n is the integer nearest the exact value of x/y; whenever| n − x/y | = 1/2, then n is even. Thus, the remainder is always exact. If r = 0, its sign shall be that ofx.’’ This definition is applicable for all implementations.

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7.12.10.3 The remquo functions
Synopsis1#include <math.h>double remquo(double x, double y, int *quo);float remquof(float x, float y, int *quo);long double remquol(long double x, long double y,
int *quo);
Description

2

The remquo functions compute the same remainder as the remainder functions. In
the object pointed to by quo they store a value whose sign is the sign of x/y and whose
magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
n is an implementation-defined integer greater than or equal to 3.
Returns3

The remquo functions return x REM y. If y is zero, the value stored in the object
pointed to by quo is unspecified and whether a domain error occurs or the functions
return zero is implementation defined.

7.12.11 Manipulation functions
7.12.11.1 The copysign functions
Synopsis1#include <math.h>double copysign(double x, double y);float copysignf(float x, float y);long double copysignl(long double x, long double y);
Description

2

The copysign functions produce a value with the magnitude of x and the sign of y.
They produce a NaN (with the sign of y) if x is a NaN. On implementations that
represent a signed zero but do not treat negative zero consistently in arithmetic
operations, the copysign functions regard the sign of zero as positive.
Returns3

The copysign functions return a value with the magnitude of x and the sign of y.

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7.12.11.2 The nan functions
Synopsis1#include <math.h>double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
Description

2

The call nan("n-char-sequence") is equivalent to strtod("NAN(n-charsequence)",(char**)NULL); the call nan("") is equivalent tostrtod("NAN()", (char**) NULL). If tagp does not point to an n-charsequence or an empty string, the call is equivalent to strtod("NAN", (char**)
NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
and strtold.
Returns

3

The nan functions return a quiet NaN, if available, with content indicated through tagp.
If the implementation does not support quiet NaNs, the functions return zero.
Forward references: the strtod, strtof, and strtold functions (7.20.1.3).

7.12.11.3 The nextafter functions
Synopsis1#include <math.h>double nextafter(double x, double y);float nextafterf(float x, float y);long double nextafterl(long double x, long double y);
Description

2

The nextafter functions determine the next representable value, in the type of thefunction, after x in the direction of y, where x and y are first converted to the type of thefunction.211) The nextafter functions return y if x equals y. A range error may occur
if the magnitude of x is the largest finite value representable in the type and the result is
infinite or not representable in the type.
Returns

3

The nextafter functions return the next representable value in the specified format
after x in the direction of y.

211) The argument values are converted to the type of the function, even by a macro implementation of thefunction.

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7.12.11.4 The nexttoward functions
Synopsis1#include <math.h>double nexttoward(double x, long double y);float nexttowardf(float x, long double y);long double nexttowardl(long double x, long double y);
Description

2

The nexttoward functions are equivalent to the nextafter functions except that thesecond parameter has type long double and the functions return y converted to thetype of the function if x equals y.212)

7.12.12 Maximum, minimum, and positive difference functions
7.12.12.1 The fdim functions
Synopsis1#include <math.h>double fdim(double x, double y);float fdimf(float x, float y);long double fdiml(long double x, long double y);
Description

2

The fdim functions determine the positive difference between their arguments:
x − y if x > y
if x ≤ y
+0
A range error may occur.
Returns

3

The fdim functions return the positive difference value.

7.12.12.2 The fmax functions
Synopsis1#include <math.h>double fmax(double x, double y);float fmaxf(float x, float y);long double fmaxl(long double x, long double y);212) The result of the nexttoward functions is determined in the type of the function, without loss ofrange or precision in a floating second argument.

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Description
2

The fmax functions determine the maximum numeric value of their arguments.213)
Returns

3

The fmax functions return the maximum numeric value of their arguments.

7.12.12.3 The fmin functions
Synopsis1#include <math.h>double fmin(double x, double y);float fminf(float x, float y);long double fminl(long double x, long double y);
Description

2

The fmin functions determine the minimum numeric value of their arguments.214)
Returns

3

The fmin functions return the minimum numeric value of their arguments.

7.12.13 Floating multiply-add
7.12.13.1 The fma functions
Synopsis1#include <math.h>double fma(double x, double y, double z);
float fmaf(float x, float y, float z);
long double fmal(long double x, long double y,long double z);
Description

2

The fma functions compute (x × y) + z, rounded as one ternary operation: they computethe value (as if) to infinite precision and round once to the result format, according to thecurrent rounding mode. A range error may occur.

Returns
3

The fma functions return (x × y) + z, rounded as one ternary operation.

213) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then thefmax functions choose the numeric value. See F.9.9.2.
214) The fmin functions are analogous to the fmax functions in their treatment of NaNs.

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7.12.14 Comparison macros
1

The relational and equality operators support the usual mathematical relationships
between numeric values. For any ordered pair of numeric values exactly one of therelationships — less, greater, and equal — is true. Relational operators may raise the‘‘invalid’’ floating-point exception when argument values are NaNs. For a NaN and anumeric value, or for two NaNs, just the unordered relationship is true.215) The following
subclauses provide macros that are quiet (non floating-point exception raising) versionsof the relational operators, and other comparison macros that facilitate writing efficientcode that accounts for NaNs without suffering the ‘‘invalid’’ floating-point exception. In
the synopses in this subclause, real-floating indicates that the argument shall be an
expression of real floating type.

7.12.14.1 The isgreater macro
Synopsis1#include <math.h>
int isgreater(real-floating x, real-floating y);
Description

2

The isgreater macro determines whether its first argument is greater than its second
argument. The value of isgreater(x, y) is always equal to (x) > (y); however,unlike (x) > (y), isgreater(x, y) does not raise the ‘‘invalid’’ floating-point
exception when x and y are unordered.
Returns3

The isgreater macro returns the value of (x) > (y).

7.12.14.2 The isgreaterequal macro
Synopsis1#include <math.h>
int isgreaterequal(real-floating x, real-floating y);
Description

2

The isgreaterequal macro determines whether its first argument is greater than orequal to its second argument. The value of isgreaterequal(x, y) is always equalto (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
not raise the ‘‘invalid’’ floating-point exception when x and y are unordered.

215) IEC 60559 requires that the built-in relational operators raise the ‘‘invalid’’ floating-point exception if
the operands compare unordered, as an error indicator for programs written without consideration of
NaNs; the result in these cases is false.

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Returns3

The isgreaterequal macro returns the value of (x) >= (y).

7.12.14.3 The isless macro
Synopsis1#include <math.h>
int isless(real-floating x, real-floating y);
Description

2

The isless macro determines whether its first argument is less than its second
argument. The value of isless(x, y) is always equal to (x) < (y); however,unlike (x) < (y), isless(x, y) does not raise the ‘‘invalid’’ floating-point
exception when x and y are unordered.
Returns3

The isless macro returns the value of (x) < (y).

7.12.14.4 The islessequal macro
Synopsis1#include <math.h>
int islessequal(real-floating x, real-floating y);
Description

2

The islessequal macro determines whether its first argument is less than or equal toits second argument. The value of islessequal(x, y) is always equal to(x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raisethe ‘‘invalid’’ floating-point exception when x and y are unordered.
Returns3

The islessequal macro returns the value of (x) <= (y).

7.12.14.5 The islessgreater macro
Synopsis1#include <math.h>
int islessgreater(real-floating x, real-floating y);
Description

2

The islessgreater macro determines whether its first argument is less than orgreater than its second argument. The islessgreater(x, y) macro is similar to(x) < (y) || (x) > (y); however, islessgreater(x, y) does not raisethe ‘‘invalid’’ floating-point exception when x and y are unordered (nor does it evaluate x
and y twice).
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Returns3

The islessgreater macro returns the value of (x) < (y) || (x) > (y).

7.12.14.6 The isunordered macro
Synopsis1#include <math.h>
int isunordered(real-floating x, real-floating y);
Description

2

The isunordered macro determines whether its arguments are unordered.
Returns3

The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.

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7.13 Nonlocal jumps <setjmp.h>
1

The header <setjmp.h> defines the macro setjmp, and declares one function and
one type, for bypassing the normal function call and return discipline.216)

2

The type declared is
jmp_bufwhich is an array type suitable for holding the information needed to restore a calling
environment. The environment of a call to the setjmp macro consists of information
sufficient for a call to the longjmp function to return execution to the correct block andinvocation of that block, were it called recursively. It does not include the state of thefloating-point status flags, of open files, or of any other component of the abstract
machine.

3

It is unspecified whether setjmp is a macro or an identifier declared with external
linkage. If a macro definition is suppressed in order to access an actual function, or aprogram defines an external identifier with the name setjmp, the behavior is undefined.

7.13.1 Save calling environment
7.13.1.1 The setjmp macro
Synopsis1#include <setjmp.h>
int setjmp(jmp_buf env);
Description

2

The setjmp macro saves its calling environment in its jmp_buf argument for later use
by the longjmp function.
Returns3

If the return is from a direct invocation, the setjmp macro returns the value zero. If the
return is from a call to the longjmp function, the setjmp macro returns a nonzero
value.
Environmental limits

4

An invocation of the setjmp macro shall appear only in one of the following contexts:— the entire controlling expression of a selection or iteration statement;— one operand of a relational or equality operator with the other operand an integer
constant expression, with the resulting expression being the entire controlling216) These functions are useful for dealing with unusual conditions encountered in a low-level function ofa program.

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expression of a selection or iteration statement;— the operand of a unary ! operator with the resulting expression being the entire
controlling expression of a selection or iteration statement; or— the entire expression of an expression statement (possibly cast to void).
5

If the invocation appears in any other context, the behavior is undefined.

7.13.2 Restore calling environment
7.13.2.1 The longjmp function
Synopsis1#include <setjmp.h>
void longjmp(jmp_buf env, int val);
Description

2

The longjmp function restores the environment saved by the most recent invocation of
the setjmp macro in the same invocation of the program with the corresponding
jmp_buf argument. If there has been no such invocation, or if the function containing
the invocation of the setjmp macro has terminated execution217) in the interim, or if the
invocation of the setjmp macro was within the scope of an identifier with variably
modified type and execution has left that scope in the interim, the behavior is undefined.

3

All accessible objects have values, and all other components of the abstract machine218)
have state, as of the time the longjmp function was called, except that the values ofobjects of automatic storage duration that are local to the function containing the
invocation of the corresponding setjmp macro that do not have volatile-qualified typeand have been changed between the setjmp invocation and longjmp call areindeterminate.
Returns

4

After longjmp is completed, program execution continues as if the corresponding
invocation of the setjmp macro had just returned the value specified by val. The
longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
the setjmp macro returns the value 1.

5

EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
might cause memory associated with a variable length array object to be squandered.

217) For example, by executing a return statement or because another longjmp call has caused atransfer to a setjmp invocation in a function earlier in the set of nested calls.
218) This includes, but is not limited to, the floating-point status flags and the state of open files.

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ISO/IEC 9899:TC3#include <setjmp.h>
jmp_buf buf;
void g(int n);void h(int n);
int n = 6;
void f(void){
int x[n];setjmp(buf);g(n);}void g(int n){
int a[n];h(n);}void h(int n){
int b[n];longjmp(buf, 2);}§7.13.2.1// valid: f is not terminated// a may remain allocated// b may remain allocated// might cause memory loss

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7.14 Signal handling <signal.h>1

The header <signal.h> declares a type and two functions and defines several macros,for handling various signals (conditions that may be reported during program execution).

2

The type defined is
sig_atomic_t
which is the (possibly volatile-qualified) integer type of an object that can be accessed as
an atomic entity, even in the presence of asynchronous interrupts.

3

The macros defined are
SIG_DFL
SIG_ERR
SIG_IGN
which expand to constant expressions with distinct values that have type compatible withthe second argument to, and the return value of, the signal function, and whose values
compare unequal to the address of any declarable function; and the following, which
expand to positive integer constant expressions with type int and distinct values that are
the signal numbers, each corresponding to the specified condition:
SIGABRT abnormal termination, such as is initiated by the abort function
SIGFPE

an erroneous arithmetic operation, such as zero divide or an operation
resulting in overflow

SIGILLdetection of an invalid function image, such as an invalid instruction

SIGINT

receipt of an interactive attention signal

SIGSEGV an invalid access to storage
SIGTERM a termination request sent to the program
4

An implementation need not generate any of these signals, except as a result of explicit
calls to the raise function. Additional signals and pointers to undeclarable functions,with macro definitions beginning, respectively, with the letters SIG and an uppercase
letter or with SIG_ and an uppercase letter,219) may also be specified by the
implementation. The complete set of signals, their semantics, and their default handlingis implementation-defined; all signal numbers shall be positive.

219) See ‘‘future library directions’’ (7.26.9). The names of the signal numbers reflect the following terms(respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,and termination.

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7.14.1 Specify signal handling7.14.1.1 The signal function
Synopsis1#include <signal.h>void (*signal(int sig, void (*func)(int)))(int);
Description

2

The signal function chooses one of three ways in which receipt of the signal number
sig is to be subsequently handled. If the value of func is SIG_DFL, default handlingfor that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
Otherwise, func shall point to a function to be called when that signal occurs. An
invocation of such a function because of a signal, or (recursively) of any further functions
called by that invocation (other than functions in the standard library), is called a signal
handler.

3

When a signal occurs and func points to a function, it is implementation-defined
whether the equivalent of signal(sig, SIG_DFL); is executed or the
implementation prevents some implementation-defined set of signals (at least includingsig) from occurring until the current signal handling has completed; in the case of
SIGILL, the implementation may alternatively define that no action is taken. Then theequivalent of (*func)(sig); is executed. If and when the function returns, if thevalue of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-definedvalue corresponding to a computational exception, the behavior is undefined; otherwise
the program will resume execution at the point it was interrupted.

4

If the signal occurs as the result of calling the abort or raise function, the signal
handler shall not call the raise function.

5

If the signal occurs other than as the result of calling the abort or raise function, thebehavior is undefined if the signal handler refers to any object with static storage duration
other than by assigning a value to an object declared as volatile sig_atomic_t, orthe signal handler calls any function in the standard library other than the abort
function, the _Exit function, or the signal function with the first argument equal to
the signal number corresponding to the signal that caused the invocation of the handler.
Furthermore, if such a call to the signal function results in a SIG_ERR return, thevalue of errno is indeterminate.220)

6

At program startup, the equivalent ofsignal(sig, SIG_IGN);

220) If any signal is generated by an asynchronous signal handler, the behavior is undefined.

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may be executed for some signals selected in an implementation-defined manner; theequivalent ofsignal(sig, SIG_DFL);
is executed for all other signals defined by the implementation.
7

The implementation shall behave as if no library function calls the signal function.
Returns8

If the request can be honored, the signal function returns the value of func for themost recent successful call to signal for the specified signal sig. Otherwise, a value of
SIG_ERR is returned and a positive value is stored in errno.
Forward references: the abort function (7.20.4.1), the exit function (7.20.4.3), the_Exit function (7.20.4.4).

7.14.2 Send signal
7.14.2.1 The raise function
Synopsis1#include <signal.h>
int raise(int sig);
Description

2

The raise function carries out the actions described in 7.14.1.1 for the signal sig. If asignal handler is called, the raise function shall not return until after the signal handler
does.
Returns3

The raise function returns zero if successful, nonzero if unsuccessful.

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7.15 Variable arguments <stdarg.h>
1

The header <stdarg.h> declares a type and defines four macros, for advancing
through a list of arguments whose number and types are not known to the called function
when it is translated.

2

A function may be called with a variable number of arguments of varying types. As
described in 6.9.1, its parameter list contains one or more parameters. The rightmost
parameter plays a special role in the access mechanism, and will be designated parmN inthis description.

3

The type declared is
va_listwhich is an object type suitable for holding information needed by the macros
va_start, va_arg, va_end, and va_copy. If access to the varying arguments isdesired, the called function shall declare an object (generally referred to as ap in thissubclause) having type va_list. The object ap may be passed as an argument toanother function; if that function invokes the va_arg macro with parameter ap, thevalue of ap in the calling function is indeterminate and shall be passed to the va_end
macro prior to any further reference to ap.221)

7.15.1 Variable argument list access macros
1

The va_start and va_arg macros described in this subclause shall be implemented
as macros, not functions. It is unspecified whether va_copy and va_end are macros or
identifiers declared with external linkage. If a macro definition is suppressed in order toaccess an actual function, or a program defines an external identifier with the same name,the behavior is undefined. Each invocation of the va_start and va_copy macros
shall be matched by a corresponding invocation of the va_end macro in the samefunction.

7.15.1.1 The va_arg macro
Synopsis1#include <stdarg.h>
type va_arg(va_list ap, type);
Description

2

The va_arg macro expands to an expression that has the specified type and the value ofthe next argument in the call. The parameter ap shall have been initialized by theva_start or va_copy macro (without an intervening invocation of the va_end
221) It is permitted to create a pointer to a va_list and pass that pointer to another function, in whichcase the original function may make further use of the original list after the other function returns.

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macro for the same ap). Each invocation of the va_arg macro modifies ap so that thevalues of successive arguments are returned in turn. The parameter type shall be a typename specified such that the type of a pointer to an object that has the specified type canbe obtained simply by postfixing a * to type. If there is no actual next argument, or if
type is not compatible with the type of the actual next argument (as promoted according
to the default argument promotions), the behavior is undefined, except for the following
cases:— one type is a signed integer type, the other type is the corresponding unsigned integer
type, and the value is representable in both types;— one type is pointer to void and the other is a pointer to a character type.
Returns
3

The first invocation of the va_arg macro after that of the va_start macro returns thevalue of the argument after that specified by parmN . Successive invocations return thevalues of the remaining arguments in succession.

7.15.1.2 The va_copy macro
Synopsis1#include <stdarg.h>void va_copy(va_list dest, va_list src);
Description

2

The va_copy macro initializes dest as a copy of src, as if the va_start macro had
been applied to dest followed by the same sequence of uses of the va_arg macro as
had previously been used to reach the present state of src. Neither the va_copy nor
va_start macro shall be invoked to reinitialize dest without an intervening
invocation of the va_end macro for the same dest.
Returns3

The va_copy macro returns no value.

7.15.1.3 The va_end macro
Synopsis1#include <stdarg.h>void va_end(va_list ap);
Description

2

The va_end macro facilitates a normal return from the function whose variable
argument list was referred to by the expansion of the va_start macro, or the function
containing the expansion of the va_copy macro, that initialized the va_list ap. The
va_end macro may modify ap so that it is no longer usable (without being reinitialized
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by the va_start or va_copy macro). If there is no corresponding invocation of theva_start or va_copy macro, or if the va_end macro is not invoked before thereturn, the behavior is undefined.
Returns3

The va_end macro returns no value.

7.15.1.4 The va_start macro
Synopsis1#include <stdarg.h>void va_start(va_list ap, parmN);
Description

2

The va_start macro shall be invoked before any access to the unnamed arguments.

3

The va_start macro initializes ap for subsequent use by the va_arg and va_end
macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
without an intervening invocation of the va_end macro for the same ap.

4

The parameter parmN is the identifier of the rightmost parameter in the variable
parameter list in the function definition (the one just before the , ...). If the parameter
parmN is declared with the register storage class, with a function or array type, orwith a type that is not compatible with the type that results after application of the default
argument promotions, the behavior is undefined.
Returns5

The va_start macro returns no value.

6

EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
more than MAXARGS arguments), then passes the array as a single argument to function f2. The number ofpointers is specified by the first argument to f1.

#include <stdarg.h>#define MAXARGS
31
void f1(int n_ptrs, ...){
va_list ap;
char *array[MAXARGS];
int ptr_no = 0;

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if (n_ptrs > MAXARGS)n_ptrs = MAXARGS;
va_start(ap, n_ptrs);
while (ptr_no < n_ptrs)
array[ptr_no++] = va_arg(ap, char *);va_end(ap);f2(n_ptrs, array);}
Each call to f1 is required to have visible the definition of the function or a declaration such as
void f1(int, ...);

7

EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after theindicated number of arguments; after f2 has been called once with the whole list, the trailing part of the listis gathered again and passed to function f4.
#include <stdarg.h>#define MAXARGS 31
void f3(int n_ptrs, int f4_after, ...){
va_list ap, ap_save;char *array[MAXARGS];
int ptr_no = 0;
if (n_ptrs > MAXARGS)n_ptrs = MAXARGS;
va_start(ap, f4_after);while (ptr_no < n_ptrs) {array[ptr_no++] = va_arg(ap, char *);if (ptr_no == f4_after)
va_copy(ap_save, ap);}
va_end(ap);f2(n_ptrs, array);// Now process the saved copy.
n_ptrs -= f4_after;
ptr_no = 0;
while (ptr_no < n_ptrs)
array[ptr_no++] = va_arg(ap_save, char *);va_end(ap_save);f4(n_ptrs, array);}252

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7.16 Boolean type and values <stdbool.h>
1

The header <stdbool.h> defines four macros.

2

The macrobool
expands to _Bool.

3

The remaining three macros are suitable for use in #if preprocessing directives. Theyare
truewhich expands to the integer constant 1,
false
which expands to the integer constant 0, and_ _bool_true_false_are_defined
which expands to the integer constant 1.

4

Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps thenredefine the macros bool, true, and false.222)

222) See ‘‘future library directions’’ (7.26.7).

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7.17 Common definitions <stddef.h>
1

The following types and macros are defined in the standard header <stddef.h>. Someare also defined in other headers, as noted in their respective subclauses.

2

The types are
ptrdiff_t
which is the signed integer type of the result of subtracting two pointers;
size_twhich is the unsigned integer type of the result of the sizeof operator; andwchar_t
which is an integer type whose range of values can represent distinct codes for all
members of the largest extended character set specified among the supported locales; thenull character shall have the code value zero. Each member of the basic character set
shall have a code value equal to its value when used as the lone character in an integer
character
constantif
animplementationdoes
notdefine_ _STDC_MB_MIGHT_NEQ_WC_ _.

3

The macros are
NULL
which expands to an implementation-defined null pointer constant; andoffsetof(type, member-designator)
which expands to an integer constant expression that has type size_t, the value of
which is the offset in bytes, to the structure member (designated by member-designator),from the beginning of its structure (designated by type). The type and member designatorshall be such that given
static type t;then the expression &(t.member-designator) evaluates to an address constant. (If thespecified member is a bit-field, the behavior is undefined.)

Recommended practice4

The types used for size_t and ptrdiff_t should not have an integer conversion rank
greater than that of signed long int unless the implementation supports objects
large enough to make this necessary.

Forward references: localization (7.11).

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7.18 Integer types <stdint.h>
1

The header <stdint.h> declares sets of integer types having specified widths, anddefines corresponding sets of macros.223) It also defines macros that specify limits ofinteger types corresponding to types defined in other standard headers.

2

Types are defined in the following categories:— integer types having certain exact widths;— integer types having at least certain specified widths;— fastest integer types having at least certain specified widths;— integer types wide enough to hold pointers to objects;— integer types having greatest width.
(Some of these types may denote the same type.)

3

Corresponding macros specify limits of the declared types and construct suitable
constants.

4

For each type described herein that the implementation provides,224) <stdint.h> shalldeclare that typedef name and define the associated macros. Conversely, for each typedescribed herein that the implementation does not provide, <stdint.h> shall notdeclare that typedef name nor shall it define the associated macros. An implementation
shall provide those types described as ‘‘required’’, but need not provide any of the others(described as ‘‘optional’’).

7.18.1 Integer types
1

When typedef names differing only in the absence or presence of the initial u are defined,
they shall denote corresponding signed and unsigned types as described in 6.2.5; animplementation providing one of these corresponding types shall also provide the other.

2

In the following descriptions, the symbol N represents an unsigned decimal integer withno leading zeros (e.g., 8 or 24, but not 04 or 048).

223) See ‘‘future library directions’’ (7.26.8).
224) Some of these types may denote implementation-defined extended integer types.

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7.18.1.1 Exact-width integer types
1

The typedef name intN_t designates a signed integer type with width N , no padding
bits, and a two’s complement representation. Thus, int8_t denotes a signed integer
type with a width of exactly 8 bits.

2

The typedef name uintN_t designates an unsigned integer type with width N . Thus,
uint24_t denotes an unsigned integer type with a width of exactly 24 bits.

3

These types are optional. However, if an implementation provides integer types withwidths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
two’s complement representation, it shall define the corresponding typedef names.

7.18.1.2 Minimum-width integer types
1

The typedef name int_leastN_t designates a signed integer type with a width of atleast N , such that no signed integer type with lesser size has at least the specified width.
Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.

2

The typedef name uint_leastN_t designates an unsigned integer type with a widthof at least N , such that no unsigned integer type with lesser size has at least the specified
width. Thus, uint_least16_t denotes an unsigned integer type with a width of atleast 16 bits.

3

The following types are required:
int_least8_t
int_least16_t
int_least32_t
int_least64_t

uint_least8_t
uint_least16_t
uint_least32_t
uint_least64_t

All other types of this form are optional.

7.18.1.3 Fastest minimum-width integer types
1

Each of the following types designates an integer type that is usually fastest225) to operatewith among all integer types that have at least the specified width.

2

The typedef name int_fastN_t designates the fastest signed integer type with a widthof at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
type with a width of at least N .

225) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
grounds for choosing one type over another, it will simply pick some integer type satisfying thesignedness and width requirements.

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The following types are required:
int_fast8_t
int_fast16_t
int_fast32_t
int_fast64_t

uint_fast8_t
uint_fast16_t
uint_fast32_t
uint_fast64_t

All other types of this form are optional.

7.18.1.4 Integer types capable of holding object pointers
1

The following type designates a signed integer type with the property that any valid
pointer to void can be converted to this type, then converted back to pointer to void,and the result will compare equal to the original pointer:
intptr_t
The following type designates an unsigned integer type with the property that any valid
pointer to void can be converted to this type, then converted back to pointer to void,and the result will compare equal to the original pointer:
uintptr_t
These types are optional.

7.18.1.5 Greatest-width integer types
1

The following type designates a signed integer type capable of representing any value ofany signed integer type:
intmax_t
The following type designates an unsigned integer type capable of representing any valueof any unsigned integer type:uintmax_t
These types are required.

7.18.2 Limits of specified-width integer types
1

The following object-like macros226) specify the minimum and maximum limits of thetypes declared in <stdint.h>. Each macro name corresponds to a similar type name in
7.18.1.

2

Each instance of any defined macro shall be replaced by a constant expression suitablefor use in #if preprocessing directives, and this expression shall have the same type as
would an expression that is an object of the corresponding type converted according to226) C++ implementations should define these macros only when _ _STDC_LIMIT_MACROS is defined
before <stdint.h> is included.

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the integer promotions. Its implementation-defined value shall be equal to or greater inmagnitude (absolute value) than the corresponding value given below, with the same sign,
except where stated to be exactly the given value.

7.18.2.1 Limits of exact-width integer types
1— minimum values of exact-width signed integer types
INTN_MIN

exactly −(2 N −1 )— maximum values of exact-width signed integer types
INTN_MAX

exactly 2 N −1 − 1— maximum values of exact-width unsigned integer types
UINTN_MAX

exactly 2 N − 1

7.18.2.2 Limits of minimum-width integer types
1— minimum values of minimum-width signed integer types−(2 N −1 − 1)

INT_LEASTN_MIN— maximum values of minimum-width signed integer types
2 N −1 − 1

INT_LEASTN_MAX— maximum values of minimum-width unsigned integer types
2N − 1

UINT_LEASTN_MAX

7.18.2.3 Limits of fastest minimum-width integer types
1— minimum values of fastest minimum-width signed integer types−(2 N −1 − 1)

INT_FASTN_MIN— maximum values of fastest minimum-width signed integer types
2 N −1 − 1

INT_FASTN_MAX— maximum values of fastest minimum-width unsigned integer types
2N − 1

UINT_FASTN_MAX

7.18.2.4 Limits of integer types capable of holding object pointers1— minimum value of pointer-holding signed integer type−(215 − 1)

INTPTR_MIN— maximum value of pointer-holding signed integer type
215 − 1INTPTR_MAX

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216 − 1UINTPTR_MAX

7.18.2.5 Limits of greatest-width integer types
1— minimum value of greatest-width signed integer type−(263 − 1)

INTMAX_MIN— maximum value of greatest-width signed integer type263 − 1

INTMAX_MAX— maximum value of greatest-width unsigned integer type
264 − 1UINTMAX_MAX

7.18.3 Limits of other integer types
1

The following object-like macros227) specify the minimum and maximum limits ofinteger types corresponding to types defined in other standard headers.

2Each instance of these macros shall be replaced by a constant expression suitable for use
in #if preprocessing directives, and this expression shall have the same type as would anexpression that is an object of the corresponding type converted according to the integer
promotions. Its implementation-defined value shall be equal to or greater in magnitude(absolute value) than the corresponding value given below, with the same sign. An
implementation shall define only the macros corresponding to those typedef names it
actually provides.228)— limits of ptrdiff_t
PTRDIFF_MIN
PTRDIFF_MAX−65535+65535— limits of sig_atomic_t
see below
see below

SIG_ATOMIC_MIN
SIG_ATOMIC_MAX— limit of size_t
SIZE_MAX

65535— limits of wchar_t227) C++ implementations should define these macros only when _ _STDC_LIMIT_MACROS is defined
before <stdint.h> is included.
228) A freestanding implementation need not provide all of these types.

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see below
see below

WCHAR_MIN
WCHAR_MAX— limits of wint_t

see below
see below

WINT_MIN
WINT_MAX3

If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
SIG_ATOMIC_MIN shall be no greater than −127 and the value of SIG_ATOMIC_MAX
shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
SIG_ATOMIC_MAX shall be no less than 255.

4

If wchar_t (see 7.17) is defined as a signed integer type, the value of WCHAR_MIN
shall be no greater than −127 and the value of WCHAR_MAX shall be no less than 127;
otherwise, wchar_t is defined as an unsigned integer type, and the value of
WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.229)

5

If wint_t (see 7.24) is defined as a signed integer type, the value of WINT_MIN shallbe no greater than −32767 and the value of WINT_MAX shall be no less than 32767;
otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
shall be 0 and the value of WINT_MAX shall be no less than 65535.

7.18.4 Macros for integer constants
1

The following function-like macros230) expand to integer constants suitable for
initializing objects that have integer types corresponding to types defined in<stdint.h>. Each macro name corresponds to a similar type name in 7.18.1.2 or
7.18.1.5.

2

The argument in any instance of these macros shall be an unsuffixed integer constant (asdefined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.

3

Each invocation of one of these macros shall expand to an integer constant expression
suitable for use in #if preprocessing directives. The type of the expression shall havethe same type as would an expression of the corresponding type converted according to
the integer promotions. The value of the expression shall be that of the argument.

229) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
character set.
230) C++ implementations should define these macros only when _ _STDC_CONSTANT_MACROS isdefined before <stdint.h> is included.

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7.18.4.1 Macros for minimum-width integer constants
1

The macro INTN_C(value) shall expand to an integer constant expression
corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
to an integer constant expression corresponding to the type uint_leastN_t. For
example, if uint_least64_t is a name for the type unsigned long long int,
then UINT64_C(0x123) might expand to the integer constant 0x123ULL.

7.18.4.2 Macros for greatest-width integer constants
1

The following macro expands to an integer constant expression having the value specified
by its argument and the type intmax_t:

INTMAX_C(value)
The following macro expands to an integer constant expression having the value specified
by its argument and the type uintmax_t:

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7.19 Input/output <stdio.h>
7.19.1 Introduction
1

The header <stdio.h> declares three types, several macros, and many functions for
performing input and output.

2

The types declared are size_t (described in 7.17);
FILE
which is an object type capable of recording all the information needed to control a
stream, including its file position indicator, a pointer to its associated buffer (if any), an
error indicator that records whether a read/write error has occurred, and an end-of-fileindicator that records whether the end of the file has been reached; andfpos_twhich is an object type other than an array type capable of recording all the informationneeded to specify uniquely every position within a file.

3

The macros are NULL (described in 7.17);_IOFBF_IOLBF_IONBF
which expand to integer constant expressions with distinct values, suitable for use as thethird argument to the setvbuf function;
BUFSIZ
which expands to an integer constant expression that is the size of the buffer used by the
setbuf function;
EOF
which expands to an integer constant expression, with type int and a negative value, thatis returned by several functions to indicate end-of-file, that is, no more input from astream;FOPEN_MAX
which expands to an integer constant expression that is the minimum number of files thatthe implementation guarantees can be open simultaneously;
FILENAME_MAX
which expands to an integer constant expression that is the size needed for an array ofchar large enough to hold the longest file name string that the implementation

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guarantees can be opened;231)
L_tmpnamwhich expands to an integer constant expression that is the size needed for an array ofchar large enough to hold a temporary file name string generated by the tmpnam
function;
SEEK_CURSEEK_END
SEEK_SET
which expand to integer constant expressions with distinct values, suitable for use as thethird argument to the fseek function;
TMP_MAX
which expands to an integer constant expression that is the maximum number of uniquefile names that can be generated by the tmpnam function;stderrstdin
stdoutwhich are expressions of type ‘‘pointer to FILE’’ that point to the FILE objects
associated, respectively, with the standard error, input, and output streams.
4

The header <wchar.h> declares a number of functions useful for wide character input
and output. The wide character input/output functions described in that subclauseprovide operations analogous to most of those described here, except that thefundamental units internal to the program are wide characters. The external
representation (in the file) is a sequence of ‘‘generalized’’ multibyte characters, as
described further in 7.19.3.

5

The input/output functions are given the following collective terms:— The wide character input functions — those functions described in 7.24 that perform
input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
fwscanf, wscanf, vfwscanf, and vwscanf.
— The wide character output functions — those functions described in 7.24 that perform
output from wide characters and wide strings: fputwc, fputws, putwc,
putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.

231) If the implementation imposes no practical limit on the length of file name strings, the value of
FILENAME_MAX should instead be the recommended size of an array intended to hold a file namestring. Of course, file name string contents are subject to other system-specific constraints; therefore
all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.

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WG14/N1256— The wide character input/output functions — the union of the ungetwc function, thewide character input functions, and the wide character output functions.
— The byte input/output functions — those functions described in this subclause that
perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,fscanf, fwrite, getc, getchar, gets, printf, putc, putchar, puts,
scanf, ungetc, vfprintf, vfscanf, vprintf, and vscanf.
Forward references: files (7.19.3), the fseek function (7.19.9.2), streams (7.19.2), thetmpnam function (7.19.4.4), <wchar.h> (7.24).

7.19.2 Streams
1

Input and output, whether to or from physical devices such as terminals and tape drives,or whether to or from files supported on structured storage devices, are mapped into
logical data streams, whose properties are more uniform than their various inputs andoutputs. Two forms of mapping are supported, for text streams and for binary
streams.232)

2

A text stream is an ordered sequence of characters composed into lines, each line
consisting of zero or more characters plus a terminating new-line character. Whether thelast line requires a terminating new-line character is implementation-defined. Characters
may have to be added, altered, or deleted on input and output to conform to differing
conventions for representing text in the host environment. Thus, there need not be a oneto-one correspondence between the characters in a stream and those in the external
representation. Data read in from a text stream will necessarily compare equal to the datathat were earlier written out to that stream only if: the data consist only of printing
characters and the control characters horizontal tab and new-line; no new-line character isimmediately preceded by space characters; and the last character is a new-line character.
Whether space characters that are written out immediately before a new-line character
appear when read in is implementation-defined.

3

A binary stream is an ordered sequence of characters that can transparently record
internal data. Data read in from a binary stream shall compare equal to the data that were
earlier written out to that stream, under the same implementation. Such a stream may,
however, have an implementation-defined number of null characters appended to the endof the stream.

4

Each stream has an orientation. After a stream is associated with an external file, but
before any operations are performed on it, the stream is without orientation. Once a wide
character input/output function has been applied to a stream without orientation, the232) An implementation need not distinguish between text streams and binary streams. In such an
implementation, there need be no new-line characters in a text stream nor any limit to the length of a
line.

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stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
been applied to a stream without orientation, the stream becomes a byte-oriented stream.
Only a call to the freopen function or the fwide function can otherwise alter theorientation of a stream. (A successful call to freopen removes any orientation.)233)
5

Byte input/output functions shall not be applied to a wide-oriented stream and wide
character input/output functions shall not be applied to a byte-oriented stream. The
remaining stream operations do not affect, and are not affected by, a stream’s orientation,
except for the following additional restrictions:— Binary wide-oriented streams have the file-positioning restrictions ascribed to bothtext and binary streams.
— For wide-oriented streams, after a successful call to a file-positioning function thatleaves the file position indicator prior to the end-of-file, a wide character output
function can overwrite a partial multibyte character; any file contents beyond thebyte(s) written are henceforth indeterminate.

6

Each wide-oriented stream has an associated mbstate_t object that stores the current
parse state of the stream. A successful call to fgetpos stores a representation of thevalue of this mbstate_t object as part of the value of the fpos_t object. A later
successful call to fsetpos using the same stored fpos_t value restores the value ofthe associated mbstate_t object as well as the position within the controlled stream.
Environmental limits

7

An implementation shall support text files with lines containing at least 254 characters,
including the terminating new-line character. The value of the macro BUFSIZ shall be atleast 256.
Forward references: the freopen function (7.19.5.4), the fwide function (7.24.3.5),
mbstate_t (7.25.1), the fgetpos function (7.19.9.1), the fsetpos function(7.19.9.3).

233) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.

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7.19.3 Files1

A stream is associated with an external file (which may be a physical device) by opening
a file, which may involve creating a new file. Creating an existing file causes its former
contents to be discarded, if necessary. If a file can support positioning requests (such as adisk file, as opposed to a terminal), then a file position indicator associated with thestream is positioned at the start (character number zero) of the file, unless the file isopened with append mode in which case it is implementation-defined whether the fileposition indicator is initially positioned at the beginning or the end of the file. The fileposition indicator is maintained by subsequent reads, writes, and positioning requests, tofacilitate an orderly progression through the file.

2

Binary files are not truncated, except as defined in 7.19.5.3. Whether a write on a text
stream causes the associated file to be truncated beyond that point is implementationdefined.

3

When a stream is unbuffered, characters are intended to appear from the source or at thedestination as soon as possible. Otherwise characters may be accumulated andtransmitted to or from the host environment as a block. When a stream is fully buffered,characters are intended to be transmitted to or from the host environment as a block whena buffer is filled. When a stream is line buffered, characters are intended to betransmitted to or from the host environment as a block when a new-line character is
encountered. Furthermore, characters are intended to be transmitted as a block to the hostenvironment when a buffer is filled, when input is requested on an unbuffered stream, or
when input is requested on a line buffered stream that requires the transmission ofcharacters from the host environment. Support for these characteristics is
implementation-defined, and may be affected via the setbuf and setvbuf functions.

4

A file may be disassociated from a controlling stream by closing the file. Output streams
are flushed (any unwritten buffer contents are transmitted to the host environment) before
the stream is disassociated from the file. The value of a pointer to a FILE object isindeterminate after the associated file is closed (including the standard text streams).
Whether a file of zero length (on which no characters have been written by an output
stream) actually exists is implementation-defined.

5

The file may be subsequently reopened, by the same or another program execution, andits contents reclaimed or modified (if it can be repositioned at its start). If the mainfunction returns to its original caller, or if the exit function is called, all open files areclosed (hence all output streams are flushed) before program termination. Other paths toprogram termination, such as calling the abort function, need not close all files
properly.

6

The address of the FILE object used to control a stream may be significant; a copy of a
FILE object need not serve in place of the original.
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7

At program startup, three text streams are predefined and need not be opened explicitly— standard input (for reading conventional input), standard output (for writing
conventional output), and standard error (for writing diagnostic output). As initiallyopened, the standard error stream is not fully buffered; the standard input and standard
output streams are fully buffered if and only if the stream can be determined not to refer
to an interactive device.

8

Functions that open additional (nontemporary) files require a file name, which is a string.
The rules for composing valid file names are implementation-defined. Whether the same
file can be simultaneously open multiple times is also implementation-defined.

9

Although both text and binary wide-oriented streams are conceptually sequences of wide
characters, the external file associated with a wide-oriented stream is a sequence ofmultibyte characters, generalized as follows:— Multibyte encodings within files may contain embedded null bytes (unlike multibyte
encodings valid for use internal to the program).
— A file need not begin nor end in the initial shift state.234)

10

Moreover, the encodings used for multibyte characters may differ among files. Both thenature and choice of such encodings are implementation-defined.

11

The wide character input functions read multibyte characters from the stream and convert
them to wide characters as if they were read by successive calls to the fgetwc function.
Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
described by the stream’s own mbstate_t object. The byte input functions readcharacters from the stream as if by successive calls to the fgetc function.

12

The wide character output functions convert wide characters to multibyte characters andwrite them to the stream as if they were written by successive calls to the fputwc
function. Each conversion occurs as if by a call to the wcrtomb function, with theconversion state described by the stream’s own mbstate_t object. The byte output
functions write characters to the stream as if by successive calls to the fputc function.

13

In some cases, some of the byte input/output functions also perform conversions between
multibyte characters and wide characters. These conversions also occur as if by calls to
the mbrtowc and wcrtomb functions.

14

An encoding error occurs if the character sequence presented to the underlying
mbrtowc function does not form a valid (generalized) multibyte character, or if the codevalue passed to the underlying wcrtomb does not correspond to a valid (generalized)

234) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
with state-dependent encoding that does not assuredly end in the initial shift state.

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multibyte character. The wide character input/output functions and the byte input/output
functions store the value of the macro EILSEQ in errno if and only if an encoding error
occurs.
Environmental limits
15

The value of FOPEN_MAX shall be at least eight, including the three standard text
streams.
Forward references: the exit function (7.20.4.3), the fgetc function (7.19.7.1), thefopen function (7.19.5.3), the fputc function (7.19.7.3), the setbuf function(7.19.5.5), the setvbuf function (7.19.5.6), the fgetwc function (7.24.3.1), thefputwc function (7.24.3.3), conversion state (7.24.6), the mbrtowc function(7.24.6.3.2), the wcrtomb function (7.24.6.3.3).

7.19.4 Operations on files
7.19.4.1 The remove function
Synopsis1#include <stdio.h>
int remove(const char *filename);
Description

2

The remove function causes the file whose name is the string pointed to by filename
to be no longer accessible by that name. A subsequent attempt to open that file using thatname will fail, unless it is created anew. If the file is open, the behavior of the remove
function is implementation-defined.
Returns3

The remove function returns zero if the operation succeeds, nonzero if it fails.

7.19.4.2 The rename function
Synopsis1#include <stdio.h>
int rename(const char *old, const char *new);Description

2

The rename function causes the file whose name is the string pointed to by old to behenceforth known by the name given by the string pointed to by new. The file named
old is no longer accessible by that name. If a file named by the string pointed to by new
exists prior to the call to the rename function, the behavior is implementation-defined.

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Returns3

The rename function returns zero if the operation succeeds, nonzero if it fails,235) inwhich case if the file existed previously it is still known by its original name.

7.19.4.3 The tmpfile function
Synopsis1#include <stdio.h>
FILE *tmpfile(void);
Description

2

The tmpfile function creates a temporary binary file that is different from any otherexisting file and that will automatically be removed when it is closed or at program
termination. If the program terminates abnormally, whether an open temporary file isremoved is implementation-defined. The file is opened for update with "wb+" mode.
Recommended practice3

It should be possible to open at least TMP_MAX temporary files during the lifetime of the
program (this limit may be shared with tmpnam) and there should be no limit on thenumber simultaneously open other than this limit and any limit on the number of open
files (FOPEN_MAX).
Returns

4

The tmpfile function returns a pointer to the stream of the file that it created. If the filecannot be created, the tmpfile function returns a null pointer.
Forward references: the fopen function (7.19.5.3).

7.19.4.4 The tmpnam function
Synopsis1#include <stdio.h>char *tmpnam(char *s);
Description

2

The tmpnam function generates a string that is a valid file name and that is not the sameas the name of an existing file.236) The function is potentially capable of generating235) Among the reasons the implementation may cause the rename function to fail are that the file is openor that it is necessary to copy its contents to effectuate its renaming.
236) Files created using strings generated by the tmpnam function are temporary only in the sense that
their names should not collide with those generated by conventional naming rules for the
implementation. It is still necessary to use the remove function to remove such files when their use
is ended, and before program termination.

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TMP_MAX different strings, but any or all of them may already be in use by existing files
and thus not be suitable return values.
3

The tmpnam function generates a different string each time it is called.

4

The implementation shall behave as if no library function calls the tmpnam function.
Returns5

If no suitable string can be generated, the tmpnam function returns a null pointer.
Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in aninternal static object and returns a pointer to that object (subsequent calls to the tmpnam
function may modify the same object). If the argument is not a null pointer, it is assumed
to point to an array of at least L_tmpnam chars; the tmpnam function writes its resultin that array and returns the argument as its value.
Environmental limits

6

The value of the macro TMP_MAX shall be at least 25.

7.19.5 File access functions
7.19.5.1 The fclose function
Synopsis1#include <stdio.h>
int fclose(FILE *stream);
Description

2

A successful call to the fclose function causes the stream pointed to by stream to be
flushed and the associated file to be closed. Any unwritten buffered data for the stream
are delivered to the host environment to be written to the file; any unread buffered data
are discarded. Whether or not the call succeeds, the stream is disassociated from the fileand any buffer set by the setbuf or setvbuf function is disassociated from the stream(and deallocated if it was automatically allocated).
Returns

3

The fclose function returns zero if the stream was successfully closed, or EOF if any
errors were detected.

7.19.5.2 The fflush function
Synopsis1#include <stdio.h>
int fflush(FILE *stream);

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Description
2

If stream points to an output stream or an update stream in which the most recent
operation was not input, the fflush function causes any unwritten data for that stream
to be delivered to the host environment to be written to the file; otherwise, the behavior isundefined.

3

If stream is a null pointer, the fflush function performs this flushing action on all
streams for which the behavior is defined above.
Returns

4

The fflush function sets the error indicator for the stream and returns EOF if a write
error occurs, otherwise it returns zero.
Forward references: the fopen function (7.19.5.3).

7.19.5.3 The fopen function
Synopsis1#include <stdio.h>
FILE *fopen(const char * restrict filename,const char * restrict mode);
Description

2

The fopen function opens the file whose name is the string pointed to by filename,and associates a stream with it.

3

The argument mode points to a string. If the string is one of the following, the file isopen in the indicated mode. Otherwise, the behavior is undefined.237)
r
w
a
rb
wb
ab
r+
w+
a+

open text file for reading
truncate to zero length or create text file for writing
append; open or create text file for writing at end-of-fileopen binary file for reading
truncate to zero length or create binary file for writing
append; open or create binary file for writing at end-of-fileopen text file for update (reading and writing)truncate to zero length or create text file for update
append; open or create text file for update, writing at end-of-file237) If the string begins with one of the above sequences, the implementation might choose to ignore theremaining characters, or it might use them to select different kinds of a file (some of which might notconform to the properties in 7.19.2).

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r+b or rb+ open binary file for update (reading and writing)w+b or wb+ truncate to zero length or create binary file for update
a+b or ab+ append; open or create binary file for update, writing at end-of-file4

Opening a file with read mode ('r' as the first character in the mode argument) fails if
the file does not exist or cannot be read.

5

Opening a file with append mode ('a' as the first character in the mode argument)
causes all subsequent writes to the file to be forced to the then current end-of-file,regardless of intervening calls to the fseek function. In some implementations, opening
a binary file with append mode ('b' as the second or third character in the above list ofmode argument values) may initially position the file position indicator for the stream
beyond the last data written, because of null character padding.

6

When a file is opened with update mode ('+' as the second or third character in theabove list of mode argument values), both input and output may be performed on theassociated stream. However, output shall not be directly followed by input without anintervening call to the fflush function or to a file positioning function (fseek,
fsetpos, or rewind), and input shall not be directly followed by output without anintervening call to a file positioning function, unless the input operation encounters endof-file. Opening (or creating) a text file with update mode may instead open (or create) abinary stream in some implementations.

7

When opened, a stream is fully buffered if and only if it can be determined not to refer toan interactive device. The error and end-of-file indicators for the stream are cleared.
Returns

8

The fopen function returns a pointer to the object controlling the stream. If the open
operation fails, fopen returns a null pointer.
Forward references: file positioning functions (7.19.9).

7.19.5.4 The freopen function
Synopsis1#include <stdio.h>
FILE *freopen(const char * restrict filename,const char * restrict mode,
FILE * restrict stream);
Description

2

The freopen function opens the file whose name is the string pointed to by filename
and associates the stream pointed to by stream with it. The mode argument is used just272

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as in the fopen function.238)
3

If filename is a null pointer, the freopen function attempts to change the mode of
the stream to that specified by mode, as if the name of the file currently associated withthe stream had been used. It is implementation-defined which changes of mode are
permitted (if any), and under what circumstances.

4

The freopen function first attempts to close any file that is associated with the specified
stream. Failure to close the file is ignored. The error and end-of-file indicators for the
stream are cleared.
Returns

5

The freopen function returns a null pointer if the open operation fails. Otherwise,
freopen returns the value of stream.

7.19.5.5 The setbuf function
Synopsis1#include <stdio.h>void setbuf(FILE * restrict stream,char * restrict buf);
Description

2

Except that it returns no value, the setbuf function is equivalent to the setvbuf
function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
is a null pointer), with the value _IONBF for mode.
Returns

3

The setbuf function returns no value.
Forward references: the setvbuf function (7.19.5.6).

7.19.5.6 The setvbuf function
Synopsis1#include <stdio.h>
int setvbuf(FILE * restrict stream,char * restrict buf,
int mode, size_t size);

238) The primary use of the freopen function is to change the file associated with a standard text stream(stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
returned by the fopen function may be assigned.

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Description
2

The setvbuf function may be used only after the stream pointed to by stream has
been associated with an open file and before any other operation (other than an
unsuccessful call to setvbuf) is performed on the stream. The argument mode
determines how stream will be buffered, as follows: _IOFBF causes input/output to be
fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
used instead of a buffer allocated by the setvbuf function239) and the argument size
specifies the size of the array; otherwise, size may determine the size of a buffer
allocated by the setvbuf function. The contents of the array at any time areindeterminate.
Returns

3

The setvbuf function returns zero on success, or nonzero if an invalid value is given
for mode or if the request cannot be honored.

7.19.6 Formatted input/output functions
1

The formatted input/output functions shall behave as if there is a sequence point after theactions associated with each specifier.240)

7.19.6.1 The fprintf function
Synopsis1#include <stdio.h>
int fprintf(FILE * restrict stream,
const char * restrict format, ...);
Description

2

The fprintf function writes output to the stream pointed to by stream, under controlof the string pointed to by format that specifies how subsequent arguments areconverted for output. If there are insufficient arguments for the format, the behavior isundefined. If the format is exhausted while arguments remain, the excess arguments areevaluated (as always) but are otherwise ignored. The fprintf function returns whenthe end of the format string is encountered.

3

The format shall be a multibyte character sequence, beginning and ending in its initial
shift state. The format is composed of zero or more directives: ordinary multibyte
characters (not %), which are copied unchanged to the output stream; and conversion

239) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
before a buffer that has automatic storage duration is deallocated upon block exit.
240) The fprintf functions perform writes to memory for the %n specifier.

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specifications, each of which results in fetching zero or more subsequent arguments,
converting them, if applicable, according to the corresponding conversion specifier, andthen writing the result to the output stream.
4

Each conversion specification is introduced by the character %. After the %, the following
appear in sequence:— Zero or more flags (in any order) that modify the meaning of the conversion
specification.
— An optional minimum field width. If the converted value has fewer characters than thefield width, it is padded with spaces (by default) on the left (or right, if the left
adjustment flag, described later, has been given) to the field width. The field width
takes the form of an asterisk * (described later) or a nonnegative decimal integer.241)— An optional precision that gives the minimum number of digits to appear for the d, i,o, u, x, and X conversions, the number of digits to appear after the decimal-point
character for a, A, e, E, f, and F conversions, the maximum number of significant
digits for the g and G conversions, or the maximum number of bytes to be written fors conversions. The precision takes the form of a period (.) followed either by anasterisk * (described later) or by an optional decimal integer; if only the period is
specified, the precision is taken as zero. If a precision appears with any otherconversion specifier, the behavior is undefined.
— An optional length modifier that specifies the size of the argument.
— A conversion specifier character that specifies the type of conversion to be applied.
5

As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
this case, an int argument supplies the field width or precision. The arguments
specifying field width, or precision, or both, shall appear (in that order) before theargument (if any) to be converted. A negative field width argument is taken as a - flag
followed by a positive field width. A negative precision argument is taken as if the
precision were omitted.

6

The flag characters and their meanings are:-

The result of the conversion is left-justified within the field. (It is right-justified if
this flag is not specified.)+

The result of a signed conversion always begins with a plus or minus sign. (Itbegins with a sign only when a negative value is converted if this flag is not241) Note that 0 is taken as a flag, not as the beginning of a field width.

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specified.)242)
space If the first character of a signed conversion is not a sign, or if a signed conversion
results in no characters, a space is prefixed to the result. If the space and + flags
both appear, the space flag is ignored.

7#

The result is converted to an ‘‘alternative form’’. For o conversion, it increases
the precision, if and only if necessary, to force the first digit of the result to be azero (if the value and precision are both 0, a single 0 is printed). For x (or X)
conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
and G conversions, the result of converting a floating-point number always
contains a decimal-point character, even if no digits follow it. (Normally, adecimal-point character appears in the result of these conversions only if a digit
follows it.) For g and G conversions, trailing zeros are not removed from theresult. For other conversions, the behavior is undefined.

0

For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros(following any indication of sign or base) are used to pad to the field width rather
than performing space padding, except when converting an infinity or NaN. If the
0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
conversions, if a precision is specified, the 0 flag is ignored. For otherconversions, the behavior is undefined.

The length modifiers and their meanings are:hhSpecifies that a following d, i, o, u, x, or X conversion specifier applies to asigned char or unsigned char argument (the argument will havebeen promoted according to the integer promotions, but its value shall be
converted to signed char or unsigned char before printing); or thata following n conversion specifier applies to a pointer to a signed charargument.

hSpecifies that a following d, i, o, u, x, or X conversion specifier applies to ashort int or unsigned short int argument (the argument will
have been promoted according to the integer promotions, but its value shallbe converted to short int or unsigned short int before printing);or that a following n conversion specifier applies to a pointer to a short
int argument.

l (ell)Specifies that a following d, i, o, u, x, or X conversion specifier applies to along int or unsigned long int argument; that a following nconversion specifier applies to a pointer to a long int argument; that a242) The results of all floating conversions of a negative zero, and of negative values that round to zero,include a minus sign.

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following c conversion specifier applies to a wint_t argument; that afollowing s conversion specifier applies to a pointer to a wchar_t
argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
specifier.
ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to along long int or unsigned long long int argument; or that afollowing n conversion specifier applies to a pointer to a long long int
argument.
jSpecifies that a following d, i, o, u, x, or X conversion specifier applies toan intmax_t or uintmax_t argument; or that a following n conversion
specifier applies to a pointer to an intmax_t argument.

zSpecifies that a following d, i, o, u, x, or X conversion specifier applies to asize_t or the corresponding signed integer type argument; or that afollowing n conversion specifier applies to a pointer to a signed integer typecorresponding to size_t argument.

tSpecifies that a following d, i, o, u, x, or X conversion specifier applies to a
ptrdiff_t or the corresponding unsigned integer type argument; or that afollowing n conversion specifier applies to a pointer to a ptrdiff_t
argument.

LSpecifies that a following a, A, e, E, f, F, g, or G conversion specifier
applies to a long double argument.

If a length modifier appears with any conversion specifier other than as specified above,
the behavior is undefined.
8

The conversion specifiers and their meanings are:d,i

The int argument is converted to signed decimal in the style [−]dddd. The
precision specifies the minimum number of digits to appear; if the value
being converted can be represented in fewer digits, it is expanded withleading zeros. The default precision is 1. The result of converting a zero
value with a precision of zero is no characters.

o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; theletters abcdef are used for x conversion and the letters ABCDEF for X
conversion. The precision specifies the minimum number of digits to appear;
if the value being converted can be represented in fewer digits, it is expandedwith leading zeros. The default precision is 1. The result of converting azero value with a precision of zero is no characters.

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A double argument representing a floating-point number is converted todecimal notation in the style [−]ddd.ddd, where the number of digits after
the decimal-point character is equal to the precision specification. If the
precision is missing, it is taken as 6; if the precision is zero and the # flag is
not specified, no decimal-point character appears. If a decimal-point
character appears, at least one digit appears before it. The value is rounded tothe appropriate number of digits.
A double argument representing an infinity is converted in one of the styles[-]inf or [-]infinity — which style is implementation-defined. A
double argument representing a NaN is converted in one of the styles[-]nan or [-]nan(n-char-sequence) — which style, and the meaning of
any n-char-sequence, is implementation-defined. The F conversion specifier
produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
respectively.243)

e,E

A double argument representing a floating-point number is converted in thestyle [−]d.ddd e±dd, where there is one digit (which is nonzero if theargument is nonzero) before the decimal-point character and the number ofdigits after it is equal to the precision; if the precision is missing, it is taken as
6; if the precision is zero and the # flag is not specified, no decimal-point
character appears. The value is rounded to the appropriate number of digits.
The E conversion specifier produces a number with E instead of e
introducing the exponent. The exponent always contains at least two digits,
and only as many more digits as necessary to represent the exponent. If thevalue is zero, the exponent is zero.
A double argument representing an infinity or NaN is converted in the styleof an f or F conversion specifier.

g,GA double argument representing a floating-point number is converted instyle f or e (or in style F or E in the case of a G conversion specifier),
depending on the value converted and the precision. Let P equal the
precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
Then, if a conversion with style E would have an exponent of X :— if P > X ≥ −4, the conversion is with style f (or F) and precisionP − (X + 1).

— otherwise, the conversion is with style e (or E) and precision P − 1.

Finally, unless the # flag is used, any trailing zeros are removed from the243) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;the # and 0 flag characters have no effect.

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fractional portion of the result and the decimal-point character is removed if
there is no fractional portion remaining.

A double argument representing an infinity or NaN is converted in the styleof an f or F conversion specifier.
a,AA double argument representing a floating-point number is converted in thestyle [−]0xh.hhhh p±d, where there is one hexadecimal digit (which isnonzero if the argument is a normalized floating-point number and isotherwise unspecified) before the decimal-point character244) and the numberof hexadecimal digits after it is equal to the precision; if the precision is
missing and FLT_RADIX is a power of 2, then the precision is sufficient foran exact representation of the value; if the precision is missing and
FLT_RADIX is not a power of 2, then the precision is sufficient todistinguish245) values of type double, except that trailing zeros may beomitted; if the precision is zero and the # flag is not specified, no decimalpoint character appears. The letters abcdef are used for a conversion andthe letters ABCDEF for A conversion. The A conversion specifier produces a
number with X and P instead of x and p. The exponent always contains atleast one digit, and only as many more digits as necessary to represent thedecimal exponent of 2. If the value is zero, the exponent is zero.
A double argument representing an infinity or NaN is converted in the styleof an f or F conversion specifier.

c

If no l length modifier is present, the int argument is converted to an
unsigned char, and the resulting character is written.
If an l length modifier is present, the wint_t argument is converted as if by
an ls conversion specification with no precision and an argument that points
to the initial element of a two-element array of wchar_t, the first element
containing the wint_t argument to the lc conversion specification and thesecond a null wide character.

s

If no l length modifier is present, the argument shall be a pointer to the initial
element of an array of character type.246) Characters from the array are244) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character sothat subsequent digits align to nibble (4-bit) boundaries.
245) The precision p is sufficient to distinguish values of the source type if 16 p−1 > b n where b is
FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller pmight suffice depending on the implementation’s scheme for determining the digit to the left of thedecimal-point character.
246) No special provisions are made for multibyte characters.

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written up to (but not including) the terminating null character. If the
precision is specified, no more than that many bytes are written. If the
precision is not specified or is greater than the size of the array, the array shallcontain a null character.
If an l length modifier is present, the argument shall be a pointer to the initial
element of an array of wchar_t type. Wide characters from the array areconverted to multibyte characters (each as if by a call to the wcrtomb
function, with the conversion state described by an mbstate_t object
initialized to zero before the first wide character is converted) up to andincluding a terminating null wide character. The resulting multibyte
characters are written up to (but not including) the terminating null character(byte). If no precision is specified, the array shall contain a null wide
character. If a precision is specified, no more than that many bytes are
written (including shift sequences, if any), and the array shall contain a nullwide character if, to equal the multibyte character sequence length given by
the precision, the function would need to access a wide character one past theend of the array. In no case is a partial multibyte character written.247)
p

The argument shall be a pointer to void. The value of the pointer isconverted to a sequence of printing characters, in an implementation-definedmanner.

n

The argument shall be a pointer to signed integer into which is written thenumber of characters written to the output stream so far by this call tofprintf. No argument is converted, but one is consumed. If the conversion
specification includes any flags, a field width, or a precision, the behavior isundefined.

%

A % character is written. No argument is converted. The complete
conversion specification shall be %%.

9

If a conversion specification is invalid, the behavior is undefined.248) If any argument is
not the correct type for the corresponding conversion specification, the behavior isundefined.

10

In no case does a nonexistent or small field width cause truncation of a field; if the resultof a conversion is wider than the field width, the field is expanded to contain theconversion result.

247) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
248) See ‘‘future library directions’’ (7.26.9).

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For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
to a hexadecimal floating number with the given precision.
Recommended practice12

For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
representable in the given precision, the result should be one of the two adjacent numbers
in hexadecimal floating style with the given precision, with the extra stipulation that theerror should have a correct sign for the current rounding direction.

13

For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
DECIMAL_DIG, then the result should be correctly rounded.249) If the number ofsignificant decimal digits is more than DECIMAL_DIG but the source value is exactly
representable with DECIMAL_DIG digits, then the result should be an exact
representation with trailing zeros. Otherwise, the source value is bounded by two
adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the valueof the resultant decimal string D should satisfy L ≤ D ≤ U, with the extra stipulation thatthe error should have a correct sign for the current rounding direction.
Returns

14

The fprintf function returns the number of characters transmitted, or a negative value
if an output or encoding error occurred.
Environmental limits

15

The number of characters that can be produced by any single conversion shall be at least
4095.

16

EXAMPLE 1
places:To print a date and time in the form ‘‘Sunday, July 3, 10:02’’ followed by π to five decimal#include <math.h>#include <stdio.h>/* ... */char *weekday, *month;// pointers to strings
int day, hour, min;fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",weekday, month, day, hour, min);fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

17

EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and themembers of the extended character set that consist of more than one byte each consist of exactly two bytes,
the first of which is denoted here by a and the second by an uppercase letter.

249) For binary-to-decimal conversion, the result format’s values are the numbers representable with thegiven format specifier. The number of significant digits is determined by the format specifier, and in
the case of fixed-point conversion by the source value as well.

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Given the following wide string with length seven,static wchar_t wstr[] = L" X Yabc Z W";
the seven calls
fprintf(stdout, "|1234567890123|\n");fprintf(stdout, "|%13ls|\n", wstr);
fprintf(stdout, "|%-13.9ls|\n", wstr);
fprintf(stdout, "|%13.10ls|\n", wstr);
fprintf(stdout, "|%13.11ls|\n", wstr);
fprintf(stdout, "|%13.15ls|\n", &wstr[2]);fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);will print the following seven lines:|1234567890123||
X Yabc Z W||
| X Yabc Z|
X Yabc Z||
X Yabc Z W||
abc Z W||
Z|

Forward references: conversion state (7.24.6), the wcrtomb function (7.24.6.3.3).

7.19.6.2 The fscanf function
Synopsis1#include <stdio.h>
int fscanf(FILE * restrict stream,
const char * restrict format, ...);
Description

2

The fscanf function reads input from the stream pointed to by stream, under controlof the string pointed to by format that specifies the admissible input sequences and how
they are to be converted for assignment, using subsequent arguments as pointers to theobjects to receive the converted input. If there are insufficient arguments for the format,
the behavior is undefined. If the format is exhausted while arguments remain, the excess
arguments are evaluated (as always) but are otherwise ignored.

3

The format shall be a multibyte character sequence, beginning and ending in its initial
shift state. The format is composed of zero or more directives: one or more white-spacecharacters, an ordinary multibyte character (neither % nor a white-space character), or aconversion specification. Each conversion specification is introduced by the character %.
After the %, the following appear in sequence:— An optional assignment-suppressing character *.
— An optional decimal integer greater than zero that specifies the maximum field width(in characters).

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ISO/IEC 9899:TC3— An optional length modifier that specifies the size of the receiving object.
— A conversion specifier character that specifies the type of conversion to be applied.
4

The fscanf function executes each directive of the format in turn. If a directive fails, asdetailed below, the function returns. Failures are described as input failures (due to theoccurrence of an encoding error or the unavailability of input characters), or matching
failures (due to inappropriate input).

5

A directive composed of white-space character(s) is executed by reading input up to thefirst non-white-space character (which remains unread), or until no more characters canbe read.

6

A directive that is an ordinary multibyte character is executed by reading the next
characters of the stream. If any of those characters differ from the ones composing thedirective, the directive fails and the differing and subsequent characters remain unread.
Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
read, the directive fails.

7

A directive that is a conversion specification defines a set of matching input sequences, as
described below for each specifier. A conversion specification is executed in thefollowing steps:

8

Input white-space characters (as specified by the isspace function) are skipped, unlessthe specification includes a [, c, or n specifier.250)

9An input item is read from the stream, unless the specification includes an n specifier. An
input item is defined as the longest sequence of input characters which does not exceed
any specified field width and which is, or is a prefix of, a matching input sequence.251)
The first character, if any, after the input item remains unread. If the length of the input
item is zero, the execution of the directive fails; this condition is a matching failure unlessend-of-file, an encoding error, or a read error prevented input from the stream, in whichcase it is an input failure.

10

Except in the case of a % specifier, the input item (or, in the case of a %n directive, thecount of input characters) is converted to a type appropriate to the conversion specifier. If
the input item is not a matching sequence, the execution of the directive fails: thiscondition is a matching failure. Unless assignment suppression was indicated by a *, theresult of the conversion is placed in the object pointed to by the first argument following
the format argument that has not already received a conversion result. If this object
does not have an appropriate type, or if the result of the conversion cannot be represented250) These white-space characters are not counted against a specified field width.
251) fscanf pushes back at most one input character onto the input stream. Therefore, some sequencesthat are acceptable to strtod, strtol, etc., are unacceptable to fscanf.

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in the object, the behavior is undefined.
11

The length modifiers and their meanings are:hhSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to signed char or unsigned char.

hSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to short int or unsigned shortint.

l (ell)Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to long int or unsigned longint; that a following a, A, e, E, f, F, g, or G conversion specifier applies toan argument with type pointer to double; or that a following c, s, or [conversion specifier applies to an argument with type pointer to wchar_t.

ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to long long int or unsigned
long long int.
jSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to intmax_t or uintmax_t.

zSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to size_t or the corresponding signed
integer type.

t

Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to ptrdiff_t or the corresponding
unsigned integer type.

L

Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
applies to an argument with type pointer to long double.

If a length modifier appears with any conversion specifier other than as specified above,
the behavior is undefined.
12

The conversion specifiers and their meanings are:dMatches an optionally signed decimal integer, whose format is the same as
expected for the subject sequence of the strtol function with the value 10
for the base argument. The corresponding argument shall be a pointer tosigned integer.

iMatches an optionally signed integer, whose format is the same as expected
for the subject sequence of the strtol function with the value 0 for thebase argument. The corresponding argument shall be a pointer to signed
integer.

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ISO/IEC 9899:TC3oMatches an optionally signed octal integer, whose format is the same as
expected for the subject sequence of the strtoul function with the value 8
for the base argument. The corresponding argument shall be a pointer tounsigned integer.

uMatches an optionally signed decimal integer, whose format is the same as
expected for the subject sequence of the strtoul function with the value 10
for the base argument. The corresponding argument shall be a pointer tounsigned integer.

xMatches an optionally signed hexadecimal integer, whose format is the same
as expected for the subject sequence of the strtoul function with the value
16 for the base argument. The corresponding argument shall be a pointer tounsigned integer.

a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
format is the same as expected for the subject sequence of the strtod
function. The corresponding argument shall be a pointer to floating.
cMatches a sequence of characters of exactly the number specified by the field
width (1 if no field width is present in the directive).252)
If no l length modifier is present, the corresponding argument shall be apointer to the initial element of a character array large enough to accept thesequence. No null character is added.
If an l length modifier is present, the input shall be a sequence of multibyte
characters that begins in the initial shift state. Each multibyte character in thesequence is converted to a wide character as if by a call to the mbrtowc
function, with the conversion state described by an mbstate_t object
initialized to zero before the first multibyte character is converted. The
corresponding argument shall be a pointer to the initial element of an array ofwchar_t large enough to accept the resulting sequence of wide characters.
No null wide character is added.

sMatches a sequence of non-white-space characters.252)
If no l length modifier is present, the corresponding argument shall be apointer to the initial element of a character array large enough to accept thesequence and a terminating null character, which will be added automatically.
If an l length modifier is present, the input shall be a sequence of multibyte

252) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [conversion specifiers — the extent of the input field is determined on a byte-by-byte basis. The
resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.

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characters that begins in the initial shift state. Each multibyte character isconverted to a wide character as if by a call to the mbrtowc function, withthe conversion state described by an mbstate_t object initialized to zero
before the first multibyte character is converted. The corresponding argument
shall be a pointer to the initial element of an array of wchar_t large enoughto accept the sequence and the terminating null wide character, which will be
added automatically.
[

Matches a nonempty sequence of characters from a set of expected characters(the scanset).252)
If no l length modifier is present, the corresponding argument shall be apointer to the initial element of a character array large enough to accept thesequence and a terminating null character, which will be added automatically.
If an l length modifier is present, the input shall be a sequence of multibyte
characters that begins in the initial shift state. Each multibyte character isconverted to a wide character as if by a call to the mbrtowc function, withthe conversion state described by an mbstate_t object initialized to zero
before the first multibyte character is converted. The corresponding argument
shall be a pointer to the initial element of an array of wchar_t large enoughto accept the sequence and the terminating null wide character, which will be
added automatically.
The conversion specifier includes all subsequent characters in the format
string, up to and including the matching right bracket (]). The characters
between the brackets (the scanlist) compose the scanset, unless the character
after the left bracket is a circumflex (^), in which case the scanset contains all
characters that do not appear in the scanlist between the circumflex and theright bracket. If the conversion specifier begins with [] or [^], the rightbracket character is in the scanlist and the next following right bracket
character is the matching right bracket that ends the specification; otherwise
the first following right bracket character is the one that ends the
specification. If a - character is in the scanlist and is not the first, nor thesecond where the first character is a ^, nor the last character, the behavior is
implementation-defined.

p286

Matches an implementation-defined set of sequences, which should be thesame as the set of sequences that may be produced by the %p conversion of
the fprintf function. The corresponding argument shall be a pointer to apointer to void. The input item is converted to a pointer value in an
implementation-defined manner. If the input item is a value converted earlier
during the same program execution, the pointer that results shall compare
equal to that value; otherwise the behavior of the %p conversion is undefined.
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No input is consumed. The corresponding argument shall be a pointer tosigned integer into which is to be written the number of characters read fromthe input stream so far by this call to the fscanf function. Execution of a%n directive does not increment the assignment count returned at thecompletion of execution of the fscanf function. No argument is converted,but one is consumed. If the conversion specification includes an assignmentsuppressing character or a field width, the behavior is undefined.

%

Matches a single % character; no conversion or assignment occurs. The
complete conversion specification shall be %%.

13

If a conversion specification is invalid, the behavior is undefined.253)

14

The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
respectively, a, e, f, g, and x.

15

Trailing white space (including new-line characters) is left unread unless matched by adirective. The success of literal matches and suppressed assignments is not directly
determinable other than via the %n directive.
Returns

16

The fscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the function returns the number of input items
assigned, which can be fewer than provided for, or even zero, in the event of an earlymatching failure.

17

EXAMPLE 1

The call:#include <stdio.h>/* ... */int n, i; float x; char name[50];n = fscanf(stdin, "%d%f%s", &i, &x, name);with the input line:
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
thompson\0.

18

EXAMPLE 2

The call:#include <stdio.h>/* ... */int i; float x; char name[50];fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);with input:

253) See ‘‘future library directions’’ (7.26.9).

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56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name thesequence 56\0. The next character read from the input stream will be a.

19

EXAMPLE 3

To accept repeatedly from stdin a quantity, a unit of measure, and an item name:#include <stdio.h>/* ... */int count; float quant; char units[21], item[21];do {count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);fscanf(stdin,"%*[^\n]");} while (!feof(stdin) && !ferror(stdin));20

If the stdin stream contains the following lines:
2 quarts of oil-12.8degrees Celsius
lots of luck
10.0LBSofdirt
100ergs of energy
the execution of the above example will be analogous to the following assignments:
quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");count = 3;
quant = -12.8; strcpy(units, "degrees");count = 2; // "C" fails to match "o"count = 0; // "l" fails to match "%f"quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");count = 3;
count = 0; // "100e" fails to match "%f"count = EOF;

21

EXAMPLE 4

In:#include <stdio.h>/* ... */int d1, d2, n1, n2, i;i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the valueof 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.

22

EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and themembers of the extended character set that consist of more than one byte each consist of exactly two bytes,
the first of which is denoted here by a and the second by an uppercase letter, but are only recognized assuch when in the alternate shift state. The shift sequences are denoted by ↑ and ↓, in which the first causes
entry into the alternate shift state.

23

After the call:288

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ISO/IEC 9899:TC3#include <stdio.h>/* ... */char str[50];fscanf(stdin, "a%s", str);with the input line:a↑ X Y↓ bc

str will contain ↑ X Y↓\0 assuming that none of the bytes of the shift sequences (or of the multibyte
characters, in the more general case) appears to be a single-byte white-space character.

24

In contrast, after the call:#include <stdio.h>#include <stddef.h>/* ... */wchar_t wstr[50];fscanf(stdin, "a%ls", wstr);with the same input line, wstr will contain the two wide characters that correspond to X and Y and aterminating null wide character.

25

However, the call:#include <stdio.h>#include <stddef.h>/* ... */wchar_t wstr[50];fscanf(stdin, "a↑ X↓%ls", wstr);with the same input line will return zero due to a matching failure against the ↓ sequence in the format
string.

26

Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
character Y, after the call:#include <stdio.h>#include <stddef.h>/* ... */wchar_t wstr[50];fscanf(stdin, "a↑ Y↓%ls", wstr);with the same input line, zero will again be returned, but stdin will be left with a partially consumed
multibyte character.

Forward references: the strtod, strtof, and strtold functions (7.20.1.3), thestrtol, strtoll, strtoul, and strtoull functions (7.20.1.4), conversion state(7.24.6), the wcrtomb function (7.24.6.3.3).

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7.19.6.3 The printf function
Synopsis1#include <stdio.h>
int printf(const char * restrict format, ...);
Description

2

The printf function is equivalent to fprintf with the argument stdout interposed
before the arguments to printf.
Returns3

The printf function returns the number of characters transmitted, or a negative value if
an output or encoding error occurred.

7.19.6.4 The scanf function
Synopsis1#include <stdio.h>
int scanf(const char * restrict format, ...);
Description

2

The scanf function is equivalent to fscanf with the argument stdin interposed
before the arguments to scanf.
Returns

3

The scanf function returns the value of the macro EOF if an input failure occurs before
any conversion. Otherwise, the scanf function returns the number of input items
assigned, which can be fewer than provided for, or even zero, in the event of an earlymatching failure.

7.19.6.5 The snprintf function
Synopsis1#include <stdio.h>
int snprintf(char * restrict s, size_t n,
const char * restrict format, ...);
Description

2

The snprintf function is equivalent to fprintf, except that the output is written into
an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
and s may be a null pointer. Otherwise, output characters beyond the n-1st are
discarded rather than being written to the array, and a null character is written at the endof the characters actually written into the array. If copying takes place between objects
that overlap, the behavior is undefined.
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Returns
3

The snprintf function returns the number of characters that would have been written
had n been sufficiently large, not counting the terminating null character, or a negativevalue if an encoding error occurred. Thus, the null-terminated output has been
completely written if and only if the returned value is nonnegative and less than n.

7.19.6.6 The sprintf function
Synopsis1#include <stdio.h>
int sprintf(char * restrict s,
const char * restrict format, ...);
Description

2

The sprintf function is equivalent to fprintf, except that the output is written into
an array (specified by the argument s) rather than to a stream. A null character is written
at the end of the characters written; it is not counted as part of the returned value. If
copying takes place between objects that overlap, the behavior is undefined.
Returns

3

The sprintf function returns the number of characters written in the array, notcounting the terminating null character, or a negative value if an encoding error occurred.

7.19.6.7 The sscanf function
Synopsis1#include <stdio.h>
int sscanf(const char * restrict s,
const char * restrict format, ...);
Description

2

The sscanf function is equivalent to fscanf, except that input is obtained from astring (specified by the argument s) rather than from a stream. Reaching the end of thestring is equivalent to encountering end-of-file for the fscanf function. If copying
takes place between objects that overlap, the behavior is undefined.
Returns

3

The sscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the sscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

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7.19.6.8 The vfprintf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vfprintf(FILE * restrict stream,
const char * restrict format,
va_list arg);
Description

2

The vfprintf function is equivalent to fprintf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vfprintf function does not invoke theva_end macro.254)
Returns3

The vfprintf function returns the number of characters transmitted, or a negativevalue if an output or encoding error occurred.

4

EXAMPLEThe following shows the use of the vfprintf function in a general error-reporting routine.

#include <stdarg.h>#include <stdio.h>void error(char *function_name, char *format, ...){
va_list args;
va_start(args, format);// print out name of function causing error
fprintf(stderr, "ERROR in %s: ", function_name);// print out remainder of message
vfprintf(stderr, format, args);
va_end(args);}254) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, andvsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

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7.19.6.9 The vfscanf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vfscanf(FILE * restrict stream,
const char * restrict format,
va_list arg);
Description

2

The vfscanf function is equivalent to fscanf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vfscanf function does not invoke theva_end macro.254)
Returns3

The vfscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the vfscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

7.19.6.10 The vprintf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vprintf(const char * restrict format,
va_list arg);
Description

2

The vprintf function is equivalent to printf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vprintf function does not invoke theva_end macro.254)
Returns3

The vprintf function returns the number of characters transmitted, or a negative value
if an output or encoding error occurred.

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7.19.6.11 The vscanf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vscanf(const char * restrict format,
va_list arg);
Description

2

The vscanf function is equivalent to scanf, with the variable argument list replacedby arg, which shall have been initialized by the va_start macro (and possiblysubsequent va_arg calls). The vscanf function does not invoke the va_end
macro.254)
Returns3

The vscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the vscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

7.19.6.12 The vsnprintf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vsnprintf(char * restrict s, size_t n,
const char * restrict format,
va_list arg);

Description
2

The vsnprintf function is equivalent to snprintf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vsnprintf function does not invoke theva_end macro.254) If copying takes place between objects that overlap, the behavior isundefined.
Returns3

The vsnprintf function returns the number of characters that would have been written
had n been sufficiently large, not counting the terminating null character, or a negativevalue if an encoding error occurred. Thus, the null-terminated output has been
completely written if and only if the returned value is nonnegative and less than n.

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7.19.6.13 The vsprintf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vsprintf(char * restrict s,
const char * restrict format,
va_list arg);
Description

2

The vsprintf function is equivalent to sprintf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vsprintf function does not invoke theva_end macro.254) If copying takes place between objects that overlap, the behavior isundefined.
Returns3

The vsprintf function returns the number of characters written in the array, notcounting the terminating null character, or a negative value if an encoding error occurred.

7.19.6.14 The vsscanf function
Synopsis1#include <stdarg.h>#include <stdio.h>
int vsscanf(const char * restrict s,
const char * restrict format,
va_list arg);
Description

2

The vsscanf function is equivalent to sscanf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vsscanf function does not invoke theva_end macro.254)
Returns3

The vsscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the vsscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

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7.19.7 Character input/output functions
7.19.7.1 The fgetc function
Synopsis1#include <stdio.h>
int fgetc(FILE *stream);
Description

2

If the end-of-file indicator for the input stream pointed to by stream is not set and anext character is present, the fgetc function obtains that character as an unsigned
char converted to an int and advances the associated file position indicator for the
stream (if defined).
Returns3

If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the endof-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, thefgetc function returns the next character from the input stream pointed to by stream.
If a read error occurs, the error indicator for the stream is set and the fgetc function
returns EOF.255)

7.19.7.2 The fgets function
Synopsis1#include <stdio.h>char *fgets(char * restrict s, int n,
FILE * restrict stream);
Description

2

The fgets function reads at most one less than the number of characters specified by nfrom the stream pointed to by stream into the array pointed to by s. No additional
characters are read after a new-line character (which is retained) or after end-of-file. A
null character is written immediately after the last character read into the array.
Returns

3

The fgets function returns s if successful. If end-of-file is encountered and no
characters have been read into the array, the contents of the array remain unchanged and anull pointer is returned. If a read error occurs during the operation, the array contents areindeterminate and a null pointer is returned.

255) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.

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7.19.7.3 The fputc function
Synopsis1#include <stdio.h>
int fputc(int c, FILE *stream);
Description

2

The fputc function writes the character specified by c (converted to an unsignedchar) to the output stream pointed to by stream, at the position indicated by the
associated file position indicator for the stream (if defined), and advances the indicator
appropriately. If the file cannot support positioning requests, or if the stream was opened
with append mode, the character is appended to the output stream.
Returns

3

The fputc function returns the character written. If a write error occurs, the error
indicator for the stream is set and fputc returns EOF.

7.19.7.4 The fputs function
Synopsis1#include <stdio.h>
int fputs(const char * restrict s,
FILE * restrict stream);
Description

2

The fputs function writes the string pointed to by s to the stream pointed to bystream. The terminating null character is not written.
Returns

3

The fputs function returns EOF if a write error occurs; otherwise it returns anonnegative value.

7.19.7.5 The getc function
Synopsis1#include <stdio.h>
int getc(FILE *stream);
Description

2

The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
may evaluate stream more than once, so the argument should never be an expression
with side effects.

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Returns
3

The getc function returns the next character from the input stream pointed to bystream. If the stream is at end-of-file, the end-of-file indicator for the stream is set andgetc returns EOF. If a read error occurs, the error indicator for the stream is set andgetc returns EOF.

7.19.7.6 The getchar function
Synopsis1#include <stdio.h>
int getchar(void);
Description

2

The getchar function is equivalent to getc with the argument stdin.
Returns

3

The getchar function returns the next character from the input stream pointed to by
stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set andgetchar returns EOF. If a read error occurs, the error indicator for the stream is set andgetchar returns EOF.

7.19.7.7 The gets function
Synopsis1#include <stdio.h>char *gets(char *s);
Description

2

The gets function reads characters from the input stream pointed to by stdin, into thearray pointed to by s, until end-of-file is encountered or a new-line character is read.
Any new-line character is discarded, and a null character is written immediately after thelast character read into the array.
Returns

3

The gets function returns s if successful. If end-of-file is encountered and no
characters have been read into the array, the contents of the array remain unchanged and anull pointer is returned. If a read error occurs during the operation, the array contents areindeterminate and a null pointer is returned.

Forward references: future library directions (7.26.9).

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7.19.7.8 The putc function
Synopsis1#include <stdio.h>
int putc(int c, FILE *stream);
Description

2

The putc function is equivalent to fputc, except that if it is implemented as a macro, it
may evaluate stream more than once, so that argument should never be an expression
with side effects.
Returns3

The putc function returns the character written. If a write error occurs, the error
indicator for the stream is set and putc returns EOF.

7.19.7.9 The putchar function
Synopsis1#include <stdio.h>
int putchar(int c);
Description

2

The putchar function is equivalent to putc with the second argument stdout.
Returns3

The putchar function returns the character written. If a write error occurs, the error
indicator for the stream is set and putchar returns EOF.

7.19.7.10 The puts function
Synopsis1#include <stdio.h>
int puts(const char *s);
Description

2

The puts function writes the string pointed to by s to the stream pointed to by stdout,
and appends a new-line character to the output. The terminating null character is not
written.
Returns3

The puts function returns EOF if a write error occurs; otherwise it returns a nonnegativevalue.

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7.19.7.11 The ungetc function
Synopsis1#include <stdio.h>
int ungetc(int c, FILE *stream);
Description

2

The ungetc function pushes the character specified by c (converted to an unsignedchar) back onto the input stream pointed to by stream. Pushed-back characters will be
returned by subsequent reads on that stream in the reverse order of their pushing. A
successful intervening call (with the stream pointed to by stream) to a file positioning
function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
stream. The external storage corresponding to the stream is unchanged.

3

One character of pushback is guaranteed. If the ungetc function is called too manytimes on the same stream without an intervening read or file positioning operation on thatstream, the operation may fail.

4

If the value of c equals that of the macro EOF, the operation fails and the input stream isunchanged.

5

A successful call to the ungetc function clears the end-of-file indicator for the stream.
The value of the file position indicator for the stream after reading or discarding all
pushed-back characters shall be the same as it was before the characters were pushed
back. For a text stream, the value of its file position indicator after a successful call to theungetc function is unspecified until all pushed-back characters are read or discarded.
For a binary stream, its file position indicator is decremented by each successful call tothe ungetc function; if its value was zero before a call, it is indeterminate after thecall.256)
Returns

6

The ungetc function returns the character pushed back after conversion, or EOF if theoperation fails.
Forward references: file positioning functions (7.19.9).

256) See ‘‘future library directions’’ (7.26.9).

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7.19.8 Direct input/output functions
7.19.8.1 The fread function
Synopsis1#include <stdio.h>
size_t fread(void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
Description

2

The fread function reads, into the array pointed to by ptr, up to nmemb elements
whose size is specified by size, from the stream pointed to by stream. For eachobject, size calls are made to the fgetc function and the results stored, in the orderread, in an array of unsigned char exactly overlaying the object. The file positionindicator for the stream (if defined) is advanced by the number of characters successfully
read. If an error occurs, the resulting value of the file position indicator for the stream isindeterminate. If a partial element is read, its value is indeterminate.
Returns

3

The fread function returns the number of elements successfully read, which may beless than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
fread returns zero and the contents of the array and the state of the stream remainunchanged.

7.19.8.2 The fwrite function
Synopsis1#include <stdio.h>
size_t fwrite(const void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
Description

2

The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
whose size is specified by size, to the stream pointed to by stream. For each object,size calls are made to the fputc function, taking the values (in order) from an array ofunsigned char exactly overlaying the object. The file position indicator for the
stream (if defined) is advanced by the number of characters successfully written. If anerror occurs, the resulting value of the file position indicator for the stream isindeterminate.

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Returns
3

The fwrite function returns the number of elements successfully written, which will beless than nmemb only if a write error is encountered. If size or nmemb is zero,fwrite returns zero and the state of the stream remains unchanged.

7.19.9 File positioning functions
7.19.9.1 The fgetpos function
Synopsis1#include <stdio.h>
int fgetpos(FILE * restrict stream,
fpos_t * restrict pos);
Description

2

The fgetpos function stores the current values of the parse state (if any) and fileposition indicator for the stream pointed to by stream in the object pointed to by pos.
The values stored contain unspecified information usable by the fsetpos function forrepositioning the stream to its position at the time of the call to the fgetpos function.
Returns3

If successful, the fgetpos function returns zero; on failure, the fgetpos function
returns nonzero and stores an implementation-defined positive value in errno.
Forward references: the fsetpos function (7.19.9.3).

7.19.9.2 The fseek function
Synopsis1#include <stdio.h>
int fseek(FILE *stream, long int offset, int whence);
Description

2

The fseek function sets the file position indicator for the stream pointed to by stream.
If a read or write error occurs, the error indicator for the stream is set and fseek fails.

3

For a binary stream, the new position, measured in characters from the beginning of thefile, is obtained by adding offset to the position specified by whence. The specified
position is the beginning of the file if whence is SEEK_SET, the current value of the fileposition indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need notmeaningfully support fseek calls with a whence value of SEEK_END.

4

For a text stream, either offset shall be zero, or offset shall be a value returned byan earlier successful call to the ftell function on a stream associated with the same fileand whence shall be SEEK_SET.
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After determining the new position, a successful call to the fseek function undoes any
effects of the ungetc function on the stream, clears the end-of-file indicator for the
stream, and then establishes the new position. After a successful fseek call, the next
operation on an update stream may be either input or output.
Returns

6

The fseek function returns nonzero only for a request that cannot be satisfied.
Forward references: the ftell function (7.19.9.4).

7.19.9.3 The fsetpos function
Synopsis1#include <stdio.h>
int fsetpos(FILE *stream, const fpos_t *pos);
Description

2

The fsetpos function sets the mbstate_t object (if any) and file position indicator
for the stream pointed to by stream according to the value of the object pointed to bypos, which shall be a value obtained from an earlier successful call to the fgetpos
function on a stream associated with the same file. If a read or write error occurs, theerror indicator for the stream is set and fsetpos fails.

3

A successful call to the fsetpos function undoes any effects of the ungetc function
on the stream, clears the end-of-file indicator for the stream, and then establishes the newparse state and position. After a successful fsetpos call, the next operation on an
update stream may be either input or output.
Returns4

If successful, the fsetpos function returns zero; on failure, the fsetpos function
returns nonzero and stores an implementation-defined positive value in errno.

7.19.9.4 The ftell function
Synopsis1#include <stdio.h>long int ftell(FILE *stream);
Description

2

The ftell function obtains the current value of the file position indicator for the stream
pointed to by stream. For a binary stream, the value is the number of characters fromthe beginning of the file. For a text stream, its file position indicator contains unspecified
information, usable by the fseek function for returning the file position indicator for the
stream to its position at the time of the ftell call; the difference between two such
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or read.
Returns3

If successful, the ftell function returns the current value of the file position indicator
for the stream. On failure, the ftell function returns −1L and stores animplementation-defined positive value in errno.

7.19.9.5 The rewind function
Synopsis1#include <stdio.h>void rewind(FILE *stream);
Description

2

The rewind function sets the file position indicator for the stream pointed to bystream to the beginning of the file. It is equivalent to(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared.
Returns3

The rewind function returns no value.

7.19.10 Error-handling functions
7.19.10.1 The clearerr function
Synopsis1#include <stdio.h>void clearerr(FILE *stream);
Description

2

The clearerr function clears the end-of-file and error indicators for the stream pointed
to by stream.
Returns3

The clearerr function returns no value.

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7.19.10.2 The feof function
Synopsis1#include <stdio.h>
int feof(FILE *stream);
Description

2

The feof function tests the end-of-file indicator for the stream pointed to by stream.
Returns

3

The feof function returns nonzero if and only if the end-of-file indicator is set for
stream.

7.19.10.3 The ferror function
Synopsis1#include <stdio.h>
int ferror(FILE *stream);
Description

2

The ferror function tests the error indicator for the stream pointed to by stream.
Returns

3

The ferror function returns nonzero if and only if the error indicator is set for
stream.

7.19.10.4 The perror function
Synopsis1#include <stdio.h>void perror(const char *s);
Description

2

The perror function maps the error number in the integer expression errno to anerror message. It writes a sequence of characters to the standard error stream thus: first(if s is not a null pointer and the character pointed to by s is not the null character), thestring pointed to by s followed by a colon (:) and a space; then an appropriate error
message string followed by a new-line character. The contents of the error message
strings are the same as those returned by the strerror function with argument errno.
Returns3

The perror function returns no value.
Forward references: the strerror function (7.21.6.2).

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7.20 General utilities <stdlib.h>
1

The header <stdlib.h> declares five types and several functions of general utility, anddefines several macros.257)

2

The types declared are size_t and wchar_t (both described in 7.17),
div_twhich is a structure type that is the type of the value returned by the div function,
ldiv_twhich is a structure type that is the type of the value returned by the ldiv function, andlldiv_t
which is a structure type that is the type of the value returned by the lldiv function.

3

The macros defined are NULL (described in 7.17);
EXIT_FAILURE
andEXIT_SUCCESS
which expand to integer constant expressions that can be used as the argument to theexit function to return unsuccessful or successful termination status, respectively, to thehost environment;
RAND_MAX
which expands to an integer constant expression that is the maximum value returned by
the rand function; and
MB_CUR_MAX
which expands to a positive integer expression with type size_t that is the maximum
number of bytes in a multibyte character for the extended character set specified by thecurrent locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.

257) See ‘‘future library directions’’ (7.26.10).

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7.20.1 Numeric conversion functions
1

The functions atof, atoi, atol, and atoll need not affect the value of the integer
expression errno on an error. If the value of the result cannot be represented, thebehavior is undefined.

7.20.1.1 The atof function
Synopsis1#include <stdlib.h>double atof(const char *nptr);
Description

2

The atof function converts the initial portion of the string pointed to by nptr to
double representation. Except for the behavior on error, it is equivalent tostrtod(nptr, (char **)NULL)
Returns3

The atof function returns the converted value.
Forward references: the strtod, strtof, and strtold functions (7.20.1.3).

7.20.1.2 The atoi, atol, and atoll functions
Synopsis1#include <stdlib.h>
int atoi(const char *nptr);
long int atol(const char *nptr);
long long int atoll(const char *nptr);
Description

2

The atoi, atol, and atoll functions convert the initial portion of the string pointed
to by nptr to int, long int, and long long int representation, respectively.
Except for the behavior on error, they are equivalent toatoi: (int)strtol(nptr, (char **)NULL, 10)
atol: strtol(nptr, (char **)NULL, 10)atoll: strtoll(nptr, (char **)NULL, 10)
Returns3

The atoi, atol, and atoll functions return the converted value.
Forward references: the strtol, strtoll, strtoul, and strtoull functions(7.20.1.4).

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7.20.1.3 The strtod, strtof, and strtold functions
Synopsis1#include <stdlib.h>double strtod(const char * restrict nptr,
char ** restrict endptr);
float strtof(const char * restrict nptr,
char ** restrict endptr);
long double strtold(const char * restrict nptr,
char ** restrict endptr);
Description

2

The strtod, strtof, and strtold functions convert the initial portion of the string
pointed to by nptr to double, float, and long double representation,
respectively. First, they decompose the input string into three parts: an initial, possibly
empty, sequence of white-space characters (as specified by the isspace function), a
subject sequence resembling a floating-point constant or representing an infinity or NaN;
and a final string of one or more unrecognized characters, including the terminating nullcharacter of the input string. Then, they attempt to convert the subject sequence to afloating-point number, and return the result.

3

The expected form of the subject sequence is an optional plus or minus sign, then one of
the following:— a nonempty sequence of decimal digits optionally containing a decimal-point
character, then an optional exponent part as defined in 6.4.4.2;— a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing adecimal-point character, then an optional binary exponent part as defined in 6.4.4.2;— INF or INFINITY, ignoring case

— NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:n-char-sequence:
digit
nondigitn-char-sequence digitn-char-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input string,
starting with the first non-white-space character, that is of the expected form. The subject
sequence contains no characters if the input string is not of the expected form.
4

If the subject sequence has the expected form for a floating-point number, the sequence ofcharacters starting with the first digit or the decimal-point character (whichever occurs
first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the308
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decimal-point character is used in place of a period, and that if neither an exponent partnor a decimal-point character appears in a decimal floating point number, or if a binary
exponent part does not appear in a hexadecimal floating point number, an exponent partof the appropriate type with value zero is assumed to follow the last digit in the string. If
the subject sequence begins with a minus sign, the sequence is interpreted as negated.258)
A character sequence INF or INFINITY is interpreted as an infinity, if representable in
the return type, else like a floating constant that is too large for the range of the return
type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet
NaN, if supported in the return type, else like a subject sequence part that does not havethe expected form; the meaning of the n-char sequences is implementation-defined.259) A
pointer to the final string is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
5

If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, thevalue resulting from the conversion is correctly rounded.

6

In other than the "C" locale, additional locale-specific subject sequence forms may be
accepted.

7

If the subject sequence is empty or does not have the expected form, no conversion is
performed; the value of nptr is stored in the object pointed to by endptr, provided
that endptr is not a null pointer.
Recommended practice8

If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, andthe result is not exactly representable, the result should be one of the two numbers in theappropriate internal format that are adjacent to the hexadecimal floating source value,with the extra stipulation that the error should have a correct sign for the current rounding
direction.

9

If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in<float.h>) significant digits, the result should be correctly rounded. If the subject
sequence D has the decimal form and more than DECIMAL_DIG significant digits,
consider the two bounding, adjacent decimal strings L and U, both having
DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L ≤ D ≤ U.
The result should be one of the (equal or adjacent) values that would be obtained bycorrectly rounding L and U according to the current rounding direction, with the extra
258) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
methods may yield different results if rounding is toward positive or negative infinity. In either case,the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
259) An implementation may use the n-char sequence to determine extra information to be represented in
the NaN’s significand.

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stipulation that the error with respect to D should have a correct sign for the current
rounding direction.260)
Returns
10

The functions return the converted value, if any. If no conversion could be performed,
zero is returned. If the correct value is outside the range of representable values, plus orminus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return
type and sign of the value), and the value of the macro ERANGE is stored in errno. If
the result underflows (7.12.1), the functions return a value whose magnitude is no greaterthan the smallest normalized positive number in the return type; whether errno acquires
the value ERANGE is implementation-defined.

7.20.1.4 The strtol, strtoll, strtoul, and strtoull functions
Synopsis1#include <stdlib.h>long int strtol(
const char * restrict nptr,
char ** restrict endptr,
int base);long long int strtoll(
const char * restrict nptr,
char ** restrict endptr,
int base);
unsigned long int strtoul(
const char * restrict nptr,
char ** restrict endptr,
int base);
unsigned long long int strtoull(const char * restrict nptr,
char ** restrict endptr,
int base);
Description

2

The strtol, strtoll, strtoul, and strtoull functions convert the initial
portion of the string pointed to by nptr to long int, long long int, unsigned
long int, and unsigned long long int representation, respectively. First,
they decompose the input string into three parts: an initial, possibly empty, sequence ofwhite-space characters (as specified by the isspace function), a subject sequence260) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually roundto the same internal floating value, but if not will round to adjacent values.

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resembling an integer represented in some radix determined by the value of base, and a
final string of one or more unrecognized characters, including the terminating nullcharacter of the input string. Then, they attempt to convert the subject sequence to an
integer, and return the result.
3

If the value of base is zero, the expected form of the subject sequence is that of an
integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
not including an integer suffix. If the value of base is between 2 and 36 (inclusive), theexpected form of the subject sequence is a sequence of letters and digits representing an
integer with the radix specified by base, optionally preceded by a plus or minus sign,
but not including an integer suffix. The letters from a (or A) through z (or Z) are
ascribed the values 10 through 35; only letters and digits whose ascribed values are lessthan that of base are permitted. If the value of base is 16, the characters 0x or 0X may
optionally precede the sequence of letters and digits, following the sign if present.

4

The subject sequence is defined as the longest initial subsequence of the input string,
starting with the first non-white-space character, that is of the expected form. The subject
sequence contains no characters if the input string is empty or consists entirely of whitespace, or if the first non-white-space character is other than a sign or a permissible letteror digit.

5

If the subject sequence has the expected form and the value of base is zero, the sequenceof characters starting with the first digit is interpreted as an integer constant according to
the rules of 6.4.4.1. If the subject sequence has the expected form and the value of baseis between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
as given above. If the subject sequence begins with a minus sign, the value resulting fromthe conversion is negated (in the return type). A pointer to the final string is stored in theobject pointed to by endptr, provided that endptr is not a null pointer.

6

In other than the "C" locale, additional locale-specific subject sequence forms may be
accepted.

7

If the subject sequence is empty or does not have the expected form, no conversion is
performed; the value of nptr is stored in the object pointed to by endptr, provided
that endptr is not a null pointer.
Returns

8

The strtol, strtoll, strtoul, and strtoull functions return the converted
value, if any. If no conversion could be performed, zero is returned. If the correct value
is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return typeand sign of the value, if any), and the value of the macro ERANGE is stored in errno.

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7.20.2 Pseudo-random sequence generation functions
7.20.2.1 The rand function
Synopsis1#include <stdlib.h>
int rand(void);
Description

2

The rand function computes a sequence of pseudo-random integers in the range 0 to
RAND_MAX.

3

The implementation shall behave as if no library function calls the rand function.
Returns4

The rand function returns a pseudo-random integer.
Environmental limits

5

The value of the RAND_MAX macro shall be at least 32767.

7.20.2.2 The srand function
Synopsis1#include <stdlib.h>void srand(unsigned int seed);
Description

2

The srand function uses the argument as a seed for a new sequence of pseudo-random
numbers to be returned by subsequent calls to rand. If srand is then called with thesame seed value, the sequence of pseudo-random numbers shall be repeated. If rand iscalled before any calls to srand have been made, the same sequence shall be generated
as when srand is first called with a seed value of 1.

3

The implementation shall behave as if no library function calls the srand function.
Returns

4

The srand function returns no value.

5

EXAMPLEThe following functions define a portable implementation of rand and srand.

static unsigned long int next = 1;
int rand(void)// RAND_MAX assumed to be 32767{
next = next * 1103515245 + 12345;
return (unsigned int)(next/65536) % 32768;}

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void srand(unsigned int seed){next = seed;}

7.20.3 Memory management functions
1

The order and contiguity of storage allocated by successive calls to the calloc,
malloc, and realloc functions is unspecified. The pointer returned if the allocation
succeeds is suitably aligned so that it may be assigned to a pointer to any type of object
and then used to access such an object or an array of such objects in the space allocated(until the space is explicitly deallocated). The lifetime of an allocated object extends
from the allocation until the deallocation. Each such allocation shall yield a pointer to an
object disjoint from any other object. The pointer returned points to the start (lowest byte
address) of the allocated space. If the space cannot be allocated, a null pointer isreturned. If the size of the space requested is zero, the behavior is implementationdefined: either a null pointer is returned, or the behavior is as if the size were somenonzero value, except that the returned pointer shall not be used to access an object.

7.20.3.1 The calloc function
Synopsis1#include <stdlib.h>void *calloc(size_t nmemb, size_t size);
Description

2

The calloc function allocates space for an array of nmemb objects, each of whose size
is size. The space is initialized to all bits zero.261)
Returns3

The calloc function returns either a null pointer or a pointer to the allocated space.

7.20.3.2 The free function
Synopsis1#include <stdlib.h>void free(void *ptr);
Description

2

The free function causes the space pointed to by ptr to be deallocated, that is, madeavailable for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
the argument does not match a pointer earlier returned by the calloc, malloc, or261) Note that this need not be the same as the representation of floating-point zero or a null pointerconstant.

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realloc function, or if the space has been deallocated by a call to free or realloc,
the behavior is undefined.
Returns
3

The free function returns no value.

7.20.3.3 The malloc function
Synopsis1#include <stdlib.h>void *malloc(size_t size);
Description

2

The malloc function allocates space for an object whose size is specified by size andwhose value is indeterminate.
Returns3

The malloc function returns either a null pointer or a pointer to the allocated space.

7.20.3.4 The realloc function
Synopsis1#include <stdlib.h>void *realloc(void *ptr, size_t size);
Description

2

The realloc function deallocates the old object pointed to by ptr and returns apointer to a new object that has the size specified by size. The contents of the new
object shall be the same as that of the old object prior to deallocation, up to the lesser ofthe new and old sizes. Any bytes in the new object beyond the size of the old object haveindeterminate values.

3

If ptr is a null pointer, the realloc function behaves like the malloc function for the
specified size. Otherwise, if ptr does not match a pointer earlier returned by thecalloc, malloc, or realloc function, or if the space has been deallocated by a callto the free or realloc function, the behavior is undefined. If memory for the new
object cannot be allocated, the old object is not deallocated and its value is unchanged.
Returns4

The realloc function returns a pointer to the new object (which may have the samevalue as a pointer to the old object), or a null pointer if the new object could not beallocated.

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7.20.4 Communication with the environment
7.20.4.1 The abort function
Synopsis1#include <stdlib.h>void abort(void);
Description

2

The abort function causes abnormal program termination to occur, unless the signal
SIGABRT is being caught and the signal handler does not return. Whether open streams
with unwritten buffered data are flushed, open streams are closed, or temporary files are
removed is implementation-defined. An implementation-defined form of the status
unsuccessful termination is returned to the host environment by means of the function
call raise(SIGABRT).
Returns3

The abort function does not return to its caller.

7.20.4.2 The atexit function
Synopsis1#include <stdlib.h>
int atexit(void (*func)(void));
Description

2

The atexit function registers the function pointed to by func, to be called without
arguments at normal program termination.
Environmental limits

3

The implementation shall support the registration of at least 32 functions.
Returns

4

The atexit function returns zero if the registration succeeds, nonzero if it fails.
Forward references: the exit function (7.20.4.3).

7.20.4.3 The exit function
Synopsis1#include <stdlib.h>void exit(int status);
Description

2

The exit function causes normal program termination to occur. If more than one call tothe exit function is executed by a program, the behavior is undefined.
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3First, all functions registered by the atexit function are called, in the reverse order of
their registration,262) except that a function is called after any previously registeredfunctions that had already been called at the time it was registered. If, during the call to
any such function, a call to the longjmp function is made that would terminate the callto the registered function, the behavior is undefined.

4

Next, all open streams with unwritten buffered data are flushed, all open streams areclosed, and all files created by the tmpfile function are removed.

5

Finally, control is returned to the host environment. If the value of status is zero or
EXIT_SUCCESS, an implementation-defined form of the status successful termination isreturned. If the value of status is EXIT_FAILURE, an implementation-defined formof the status unsuccessful termination is returned. Otherwise the status returned is
implementation-defined.
Returns

6

The exit function cannot return to its caller.

7.20.4.4 The _Exit function
Synopsis1#include <stdlib.h>void _Exit(int status);
Description

2

The _Exit function causes normal program termination to occur and control to be
returned to the host environment. No functions registered by the atexit function orsignal handlers registered by the signal function are called. The status returned to thehost environment is determined in the same way as for the exit function (7.20.4.3).
Whether open streams with unwritten buffered data are flushed, open streams are closed,or temporary files are removed is implementation-defined.
Returns3

The _Exit function cannot return to its caller.

262) Each function is called as many times as it was registered, and in the correct order with respect toother registered functions.

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7.20.4.5 The getenv function
Synopsis1#include <stdlib.h>char *getenv(const char *name);
Description

2

The getenv function searches an environment list, provided by the host environment,
for a string that matches the string pointed to by name. The set of environment names
and the method for altering the environment list are implementation-defined.

3

The implementation shall behave as if no library function calls the getenv function.
Returns

4

The getenv function returns a pointer to a string associated with the matched list
member. The string pointed to shall not be modified by the program, but may beoverwritten by a subsequent call to the getenv function. If the specified name cannot
be found, a null pointer is returned.

7.20.4.6 The system function
Synopsis1#include <stdlib.h>
int system(const char *string);
Description

2

If string is a null pointer, the system function determines whether the hostenvironment has a command processor. If string is not a null pointer, the system
function passes the string pointed to by string to that command processor to be
executed in a manner which the implementation shall document; this might then cause theprogram calling system to behave in a non-conforming manner or to terminate.
Returns3

If the argument is a null pointer, the system function returns nonzero only if acommand processor is available. If the argument is not a null pointer, and the system
function does return, it returns an implementation-defined value.

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7.20.5 Searching and sorting utilities
1

These utilities make use of a comparison function to search or sort arrays of unspecified
type. Where an argument declared as size_t nmemb specifies the length of the arrayfor a function, nmemb can have the value zero on a call to that function; the comparison
function is not called, a search finds no matching element, and sorting performs norearrangement. Pointer arguments on such a call shall still have valid values, as describedin 7.1.4.

2

The implementation shall ensure that the second argument of the comparison function(when called from bsearch), or both arguments (when called from qsort), arepointers to elements of the array.263) The first argument when called from bsearchshall equal key.

3

The comparison function shall not alter the contents of the array. The implementation
may reorder elements of the array between calls to the comparison function, but shall notalter the contents of any individual element.

4

When the same objects (consisting of size bytes, irrespective of their current positionsin the array) are passed more than once to the comparison function, the results shall beconsistent with one another. That is, for qsort they shall define a total ordering on thearray, and for bsearch the same object shall always compare the same way with thekey.

5

A sequence point occurs immediately before and immediately after each call to thecomparison function, and also between any call to the comparison function and any
movement of the objects passed as arguments to that call.

7.20.5.1 The bsearch function
Synopsis1#include <stdlib.h>void *bsearch(const void *key, const void *base,size_t nmemb, size_t size,int (*compar)(const void *, const void *));
Description

2

The bsearch function searches an array of nmemb objects, the initial element of whichis pointed to by base, for an element that matches the object pointed to by key. The

263) That is, if the value passed is p, then the following expressions are always nonzero:((char *)p - (char *)base) % size == 0(char *)p >= (char *)base(char *)p < (char *)base + nmemb * size

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size of each element of the array is specified by size.
3

The comparison function pointed to by compar is called with two arguments that point
to the key object and to an array element, in that order. The function shall return an
integer less than, equal to, or greater than zero if the key object is considered,respectively, to be less than, to match, or to be greater than the array element. The array
shall consist of: all the elements that compare less than, all the elements that compare
equal to, and all the elements that compare greater than the key object, in that order.264)
Returns

4

The bsearch function returns a pointer to a matching element of the array, or a nullpointer if no match is found. If two elements compare as equal, which element ismatched is unspecified.

7.20.5.2 The qsort function
Synopsis1#include <stdlib.h>void qsort(void *base, size_t nmemb, size_t size,int (*compar)(const void *, const void *));
Description

2

The qsort function sorts an array of nmemb objects, the initial element of which ispointed to by base. The size of each object is specified by size.

3

The contents of the array are sorted into ascending order according to a comparison
function pointed to by compar, which is called with two arguments that point to theobjects being compared. The function shall return an integer less than, equal to, or
greater than zero if the first argument is considered to be respectively less than, equal to,or greater than the second.

4

If two elements compare as equal, their order in the resulting sorted array is unspecified.
Returns5

The qsort function returns no value.

264) In practice, the entire array is sorted according to the comparison function.

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7.20.6 Integer arithmetic functions
7.20.6.1 The abs, labs and llabs functions
Synopsis1#include <stdlib.h>
int abs(int j);long int labs(long int j);long long int llabs(long long int j);
Description

2

The abs, labs, and llabs functions compute the absolute value of an integer j. If theresult cannot be represented, the behavior is undefined.265)
Returns3

The abs, labs, and llabs, functions return the absolute value.

7.20.6.2 The div, ldiv, and lldiv functions
Synopsis1#include <stdlib.h>
div_t div(int numer, int denom);
ldiv_t ldiv(long int numer, long int denom);
lldiv_t lldiv(long long int numer, long long int denom);
Description

2

The div, ldiv, and lldiv, functions compute numer / denom and numer %denom in a single operation.
Returns3

The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, andlldiv_t, respectively, comprising both the quotient and the remainder. The structures
shall contain (in either order) the members quot (the quotient) and rem (the remainder),each of which has the same type as the arguments numer and denom. If either part of
the result cannot be represented, the behavior is undefined.

265) The absolute value of the most negative number cannot be represented in two’s complement.

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7.20.7 Multibyte/wide character conversion functions
1

The behavior of the multibyte character functions is affected by the LC_CTYPE categoryof the current locale. For a state-dependent encoding, each function is placed into its
initial conversion state by a call for which its character pointer argument, s, is a nullpointer. Subsequent calls with s as other than a null pointer cause the internal conversion
state of the function to be altered as necessary. A call with s as a null pointer causes
these functions to return a nonzero value if encodings have state dependency, and zerootherwise.266) Changing the LC_CTYPE category causes the conversion state of thesefunctions to be indeterminate.

7.20.7.1 The mblen function
Synopsis1#include <stdlib.h>
int mblen(const char *s, size_t n);
Description2

If s is not a null pointer, the mblen function determines the number of bytes containedin the multibyte character pointed to by s. Except that the conversion state of the
mbtowc function is not affected, it is equivalent tombtowc((wchar_t *)0, s, n);3

The implementation shall behave as if no library function calls the mblen function.
Returns

4

If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
character encodings, respectively, do or do not have state-dependent encodings. If s is
not a null pointer, the mblen function either returns 0 (if s points to the null character),or returns the number of bytes that are contained in the multibyte character (if the next n
or fewer bytes form a valid multibyte character), or returns −1 (if they do not form a valid
multibyte character).
Forward references: the mbtowc function (7.20.7.2).

266) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
character codes, but are grouped with an adjacent multibyte character.

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7.20.7.2 The mbtowc function
Synopsis1#include <stdlib.h>
int mbtowc(wchar_t * restrict pwc,
const char * restrict s,size_t n);
Description2

If s is not a null pointer, the mbtowc function inspects at most n bytes beginning withthe byte pointed to by s to determine the number of bytes needed to complete the next
multibyte character (including any shift sequences). If the function determines that thenext multibyte character is complete and valid, it determines the value of thecorresponding wide character and then, if pwc is not a null pointer, stores that value inthe object pointed to by pwc. If the corresponding wide character is the null wide
character, the function is left in the initial conversion state.

3

The implementation shall behave as if no library function calls the mbtowc function.
Returns

4

If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
character encodings, respectively, do or do not have state-dependent encodings. If s is
not a null pointer, the mbtowc function either returns 0 (if s points to the null character),or returns the number of bytes that are contained in the converted multibyte character (ifthe next n or fewer bytes form a valid multibyte character), or returns −1 (if they do notform a valid multibyte character).

5

In no case will the value returned be greater than n or the value of the MB_CUR_MAX
macro.

7.20.7.3 The wctomb function
Synopsis1#include <stdlib.h>
int wctomb(char *s, wchar_t wc);
Description

2

The wctomb function determines the number of bytes needed to represent the multibyte
character corresponding to the wide character given by wc (including any shift
sequences), and stores the multibyte character representation in the array whose firstelement is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
sequence needed to restore the initial shift state, and the function is left in the initialconversion state.
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The implementation shall behave as if no library function calls the wctomb function.
Returns

4

If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
character encodings, respectively, do or do not have state-dependent encodings. If s is
not a null pointer, the wctomb function returns −1 if the value of wc does not correspondto a valid multibyte character, or returns the number of bytes that are contained in themultibyte character corresponding to the value of wc.

5

In no case will the value returned be greater than the value of the MB_CUR_MAX macro.

7.20.8 Multibyte/wide string conversion functions
1

The behavior of the multibyte string functions is affected by the LC_CTYPE category of
the current locale.

7.20.8.1 The mbstowcs function
Synopsis1#include <stdlib.h>size_t mbstowcs(wchar_t * restrict pwcs,
const char * restrict s,size_t n);
Description

2

The mbstowcs function converts a sequence of multibyte characters that begins in theinitial shift state from the array pointed to by s into a sequence of corresponding wide
characters and stores not more than n wide characters into the array pointed to by pwcs.
No multibyte characters that follow a null character (which is converted into a null wide
character) will be examined or converted. Each multibyte character is converted as if by
a call to the mbtowc function, except that the conversion state of the mbtowc function is
not affected.

3

No more than n elements will be modified in the array pointed to by pwcs. If copying
takes place between objects that overlap, the behavior is undefined.
Returns

4

If an invalid multibyte character is encountered, the mbstowcs function returns(size_t)(-1). Otherwise, the mbstowcs function returns the number of arrayelements modified, not including a terminating null wide character, if any.267)

267) The array will not be null-terminated if the value returned is n.

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7.20.8.2 The wcstombs function
Synopsis1#include <stdlib.h>size_t wcstombs(char * restrict s,
const wchar_t * restrict pwcs,
size_t n);
Description

2

The wcstombs function converts a sequence of wide characters from the array pointed
to by pwcs into a sequence of corresponding multibyte characters that begins in theinitial shift state, and stores these multibyte characters into the array pointed to by s,
stopping if a multibyte character would exceed the limit of n total bytes or if a nullcharacter is stored. Each wide character is converted as if by a call to the wctomb
function, except that the conversion state of the wctomb function is not affected.

3

No more than n bytes will be modified in the array pointed to by s. If copying takes place
between objects that overlap, the behavior is undefined.
Returns4

If a wide character is encountered that does not correspond to a valid multibyte character,the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
returns the number of bytes modified, not including a terminating null character, if
any.267)324

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7.21 String handling <string.h>
7.21.1 String function conventions
1

The header <string.h> declares one type and several functions, and defines one
macro useful for manipulating arrays of character type and other objects treated as arraysof character type.268) The type is size_t and the macro is NULL (both described in7.17). Various methods are used for determining the lengths of the arrays, but in all casesa char * or void * argument points to the initial (lowest addressed) character of thearray. If an array is accessed beyond the end of an object, the behavior is undefined.

2

Where an argument declared as size_t n specifies the length of the array for afunction, n can have the value zero on a call to that function. Unless explicitly statedotherwise in the description of a particular function in this subclause, pointer arguments
on such a call shall still have valid values, as described in 7.1.4. On such a call, afunction that locates a character finds no occurrence, a function that compares two
character sequences returns zero, and a function that copies characters copies zero
characters.

3

For all functions in this subclause, each character shall be interpreted as if it had the typeunsigned char (and therefore every possible object representation is valid and has adifferent value).

7.21.2 Copying functions
7.21.2.1 The memcpy function
Synopsis1#include <string.h>void *memcpy(void * restrict s1,
const void * restrict s2,
size_t n);
Description

2

The memcpy function copies n characters from the object pointed to by s2 into theobject pointed to by s1. If copying takes place between objects that overlap, the behavior
is undefined.
Returns3

The memcpy function returns the value of s1.

268) See ‘‘future library directions’’ (7.26.11).

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7.21.2.2 The memmove function
Synopsis1#include <string.h>void *memmove(void *s1, const void *s2, size_t n);
Description

2

The memmove function copies n characters from the object pointed to by s2 into theobject pointed to by s1. Copying takes place as if the n characters from the object
pointed to by s2 are first copied into a temporary array of n characters that does notoverlap the objects pointed to by s1 and s2, and then the n characters from thetemporary array are copied into the object pointed to by s1.
Returns3

The memmove function returns the value of s1.

7.21.2.3 The strcpy function
Synopsis1#include <string.h>char *strcpy(char * restrict s1,
const char * restrict s2);
Description

2

The strcpy function copies the string pointed to by s2 (including the terminating nullcharacter) into the array pointed to by s1. If copying takes place between objects thatoverlap, the behavior is undefined.
Returns

3

The strcpy function returns the value of s1.

7.21.2.4 The strncpy function
Synopsis1#include <string.h>char *strncpy(char * restrict s1,
const char * restrict s2,
size_t n);
Description

2

The strncpy function copies not more than n characters (characters that follow a nullcharacter are not copied) from the array pointed to by s2 to the array pointed to by326

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s1.269) If copying takes place between objects that overlap, the behavior is undefined.
3

If the array pointed to by s2 is a string that is shorter than n characters, null characters
are appended to the copy in the array pointed to by s1, until n characters in all have been
written.
Returns

4

The strncpy function returns the value of s1.

7.21.3 Concatenation functions
7.21.3.1 The strcat function
Synopsis1#include <string.h>char *strcat(char * restrict s1,
const char * restrict s2);
Description

2

The strcat function appends a copy of the string pointed to by s2 (including theterminating null character) to the end of the string pointed to by s1. The initial characterof s2 overwrites the null character at the end of s1. If copying takes place between
objects that overlap, the behavior is undefined.
Returns

3

The strcat function returns the value of s1.

7.21.3.2 The strncat function
Synopsis1#include <string.h>char *strncat(char * restrict s1,
const char * restrict s2,
size_t n);
Description

2

The strncat function appends not more than n characters (a null character andcharacters that follow it are not appended) from the array pointed to by s2 to the end of
the string pointed to by s1. The initial character of s2 overwrites the null character at theend of s1. A terminating null character is always appended to the result.270) If copying269) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
not be null-terminated.
270) Thus, the maximum number of characters that can end up in the array pointed to by s1 isstrlen(s1)+n+1.

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takes place between objects that overlap, the behavior is undefined.
Returns
3

The strncat function returns the value of s1.
Forward references: the strlen function (7.21.6.3).

7.21.4 Comparison functions
1

The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
and strncmp is determined by the sign of the difference between the values of the firstpair of characters (both interpreted as unsigned char) that differ in the objects being
compared.

7.21.4.1 The memcmp function
Synopsis1#include <string.h>
int memcmp(const void *s1, const void *s2, size_t n);
Description

2

The memcmp function compares the first n characters of the object pointed to by s1 to
the first n characters of the object pointed to by s2.271)
Returns3

The memcmp function returns an integer greater than, equal to, or less than zero,accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
pointed to by s2.

7.21.4.2 The strcmp function
Synopsis1#include <string.h>
int strcmp(const char *s1, const char *s2);
Description

2

The strcmp function compares the string pointed to by s1 to the string pointed to bys2.
Returns

3

The strcmp function returns an integer greater than, equal to, or less than zero,accordingly as the string pointed to by s1 is greater than, equal to, or less than the string271) The contents of ‘‘holes’’ used as padding for purposes of alignment within structure objects areindeterminate. Strings shorter than their allocated space and unions may also cause problems incomparison.

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pointed to by s2.

7.21.4.3 The strcoll function
Synopsis1#include <string.h>
int strcoll(const char *s1, const char *s2);
Description

2

The strcoll function compares the string pointed to by s1 to the string pointed to bys2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
Returns

3

The strcoll function returns an integer greater than, equal to, or less than zero,accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
pointed to by s2 when both are interpreted as appropriate to the current locale.

7.21.4.4 The strncmp function
Synopsis1#include <string.h>
int strncmp(const char *s1, const char *s2, size_t n);
Description

2

The strncmp function compares not more than n characters (characters that follow anull character are not compared) from the array pointed to by s1 to the array pointed toby s2.
Returns

3

The strncmp function returns an integer greater than, equal to, or less than zero,accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
to, or less than the possibly null-terminated array pointed to by s2.

7.21.4.5 The strxfrm function
Synopsis1#include <string.h>size_t strxfrm(char * restrict s1,
const char * restrict s2,
size_t n);
Description

2

The strxfrm function transforms the string pointed to by s2 and places the resulting
string into the array pointed to by s1. The transformation is such that if the strcmp
function is applied to two transformed strings, it returns a value greater than, equal to, or§7.21.4.5

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less than zero, corresponding to the result of the strcoll function applied to the sametwo original strings. No more than n characters are placed into the resulting arraypointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
be a null pointer. If copying takes place between objects that overlap, the behavior isundefined.
Returns
3

The strxfrm function returns the length of the transformed string (not including theterminating null character). If the value returned is n or more, the contents of the arraypointed to by s1 are indeterminate.

4

EXAMPLE The value of the following expression is the size of the array needed to hold thetransformation of the string pointed to by s.
1 + strxfrm(NULL, s, 0)

7.21.5 Search functions
7.21.5.1 The memchr function
Synopsis1#include <string.h>void *memchr(const void *s, int c, size_t n);
Description

2

The memchr function locates the first occurrence of c (converted to an unsignedchar) in the initial n characters (each interpreted as unsigned char) of the object
pointed to by s.
Returns3

The memchr function returns a pointer to the located character, or a null pointer if thecharacter does not occur in the object.

7.21.5.2 The strchr function
Synopsis1#include <string.h>char *strchr(const char *s, int c);
Description

2

The strchr function locates the first occurrence of c (converted to a char) in thestring pointed to by s. The terminating null character is considered to be part of thestring.
Returns

3

The strchr function returns a pointer to the located character, or a null pointer if thecharacter does not occur in the string.
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7.21.5.3 The strcspn function
Synopsis1#include <string.h>size_t strcspn(const char *s1, const char *s2);
Description

2

The strcspn function computes the length of the maximum initial segment of the string
pointed to by s1 which consists entirely of characters not from the string pointed to bys2.
Returns

3

The strcspn function returns the length of the segment.

7.21.5.4 The strpbrk function
Synopsis1#include <string.h>char *strpbrk(const char *s1, const char *s2);
Description

2

The strpbrk function locates the first occurrence in the string pointed to by s1 of any
character from the string pointed to by s2.
Returns

3

The strpbrk function returns a pointer to the character, or a null pointer if no characterfrom s2 occurs in s1.

7.21.5.5 The strrchr function
Synopsis1#include <string.h>char *strrchr(const char *s, int c);
Description

2

The strrchr function locates the last occurrence of c (converted to a char) in thestring pointed to by s. The terminating null character is considered to be part of thestring.
Returns

3

The strrchr function returns a pointer to the character, or a null pointer if c does notoccur in the string.

§7.21.5.5

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7.21.5.6 The strspn function
Synopsis1#include <string.h>size_t strspn(const char *s1, const char *s2);
Description

2

The strspn function computes the length of the maximum initial segment of the string
pointed to by s1 which consists entirely of characters from the string pointed to by s2.
Returns

3

The strspn function returns the length of the segment.

7.21.5.7 The strstr function
Synopsis1#include <string.h>char *strstr(const char *s1, const char *s2);
Description

2

The strstr function locates the first occurrence in the string pointed to by s1 of thesequence of characters (excluding the terminating null character) in the string pointed toby s2.
Returns

3

The strstr function returns a pointer to the located string, or a null pointer if the string
is not found. If s2 points to a string with zero length, the function returns s1.

7.21.5.8 The strtok function
Synopsis1#include <string.h>char *strtok(char * restrict s1,
const char * restrict s2);
Description

2

A sequence of calls to the strtok function breaks the string pointed to by s1 into asequence of tokens, each of which is delimited by a character from the string pointed toby s2. The first call in the sequence has a non-null first argument; subsequent calls in thesequence have a null first argument. The separator string pointed to by s2 may bedifferent from call to call.

3

The first call in the sequence searches the string pointed to by s1 for the first character
that is not contained in the current separator string pointed to by s2. If no such character
is found, then there are no tokens in the string pointed to by s1 and the strtok function332

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returns a null pointer. If such a character is found, it is the start of the first token.
4

The strtok function then searches from there for a character that is contained in thecurrent separator string. If no such character is found, the current token extends to theend of the string pointed to by s1, and subsequent searches for a token will return a nullpointer. If such a character is found, it is overwritten by a null character, which
terminates the current token. The strtok function saves a pointer to the following
character, from which the next search for a token will start.

5

Each subsequent call, with a null pointer as the value of the first argument, starts
searching from the saved pointer and behaves as described above.

6

The implementation shall behave as if no library function calls the strtok function.
Returns

7

The strtok function returns a pointer to the first character of a token, or a null pointerif there is no token.

8

EXAMPLE#include <string.h>static char str[] = "?a???b,,,#c";char *t;t = strtok(str, "?");// t points to the token "a"t = strtok(NULL, ","); // t points to the token "??b"t = strtok(NULL, "#,"); // t points to the token "c"t = strtok(NULL, "?"); // t is a null pointer7.21.6 Miscellaneous functions
7.21.6.1 The memset function
Synopsis1#include <string.h>void *memset(void *s, int c, size_t n);
Description

2

The memset function copies the value of c (converted to an unsigned char) into
each of the first n characters of the object pointed to by s.
Returns3

The memset function returns the value of s.

§7.21.6.1

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7.21.6.2 The strerror function
Synopsis1#include <string.h>char *strerror(int errnum);
Description

2

The strerror function maps the number in errnum to a message string. Typically,
the values for errnum come from errno, but strerror shall map any value of type
int to a message.

3

The implementation shall behave as if no library function calls the strerror function.
Returns

4

The strerror function returns a pointer to the string, the contents of which are localespecific. The array pointed to shall not be modified by the program, but may beoverwritten by a subsequent call to the strerror function.

7.21.6.3 The strlen function
Synopsis1#include <string.h>size_t strlen(const char *s);
Description

2

The strlen function computes the length of the string pointed to by s.
Returns

3

The strlen function returns the number of characters that precede the terminating nullcharacter.

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7.22 Type-generic math <tgmath.h>
1

The header <tgmath.h> includes the headers <math.h> and <complex.h> anddefines several type-generic macros.

2

Of the <math.h> and <complex.h> functions without an f (float) or l (longdouble) suffix, several have one or more parameters whose corresponding real type isdouble. For each such function, except modf, there is a corresponding type-genericmacro.272) The parameters whose corresponding real type is double in the function
synopsis are generic parameters. Use of the macro invokes a function whose
corresponding real type and type domain are determined by the arguments for the genericparameters.273)

3

Use of the macro invokes a function whose generic parameters have the corresponding
real type determined as follows:— First, if any argument for generic parameters has type long double, the typedetermined is long double.
— Otherwise, if any argument for generic parameters has type double or is of integer
type, the type determined is double.
— Otherwise, the type determined is float.

4

For each unsuffixed function in <math.h> for which there is a function in<complex.h> with the same name except for a c prefix, the corresponding typegeneric macro (for both functions) has the same name as the function in <math.h>. The
corresponding type-generic macro for fabs and cabs is fabs.

272) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed tomake available the corresponding ordinary function.
273) If the type of the argument is not compatible with the type of the parameter for the selected function,
the behavior is undefined.

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acos
asin
atan
acosh
asinh
atanh
cos
sin
tan
cosh
sinh
tanh
exp
log
pow
sqrt
fabs

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<complex.h>function
cacos
casin
catan
cacoshcasinhcatanh
ccos
csin
ctan
ccosh
csinh
ctanh
cexp
clog
cpow
csqrt
cabs

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type-generic
macro
acos
asin
atan
acosh
asinh
atanh
cos
sin
tan
cosh
sinh
tanh
exp
log
pow
sqrt
fabs

If at least one argument for a generic parameter is complex, then use of the macro invokes
a complex function; otherwise, use of the macro invokes a real function.
5

For each unsuffixed function in <math.h> without a c-prefixed counterpart in<complex.h> (except modf), the corresponding type-generic macro has the same
name as the function. These type-generic macros are:

atan2
cbrt
ceil
copysign
erf
erfc
exp2
expm1
fdim
floor

fma
fmax
fmin
fmod
frexp
hypot
ilogb
ldexp
lgammallrintllround
log10
log1p
log2
logb
lrint
lroundnearbyint
nextafter
nexttowardremainder
remquorint
round
scalbnscalblntgammatrunc

If all arguments for generic parameters are real, then use of the macro invokes a realfunction; otherwise, use of the macro results in undefined behavior.
6

For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to afunction in <math.h>, the corresponding type-generic macro has the same name as thefunction. These type-generic macros are:336

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creal

Use of the macro with any real or complex argument invokes a complex function.
7

EXAMPLEWith the declarations#include <tgmath.h>
int n;
float f;double d;long double ld;
float complex fc;
double complex dc;
long double complex ldc;
functions invoked by use of type-generic macros are shown in the following table:
macro use
exp(n)
acosh(f)sin(d)
atan(ld)log(fc)sqrt(dc)
pow(ldc, f)
remainder(n, n)
nextafter(d, f)
nexttoward(f, ld)
copysign(n, ld)ceil(fc)rint(dc)fmax(ldc, ld)carg(n)cproj(f)creal(d)cimag(ld)fabs(fc)carg(dc)
cproj(ldc)§7.22

invokesexp(n), the function
acoshf(f)sin(d), the function
atanl(ld)clogf(fc)csqrt(dc)cpowl(ldc, f)
remainder(n, n), the function
nextafter(d, f), the function
nexttowardf(f, ld)
copysignl(n, ld)
undefined behavior
undefined behavior
undefined behaviorcarg(n), the function
cprojf(f)creal(d), the function
cimagl(ld)cabsf(fc)carg(dc), the function
cprojl(ldc)

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7.23 Date and time <time.h>
7.23.1 Components of time1

The header <time.h> defines two macros, and declares several types and functions for
manipulating time. Many functions deal with a calendar time that represents the current
date (according to the Gregorian calendar) and time. Some functions deal with local
time, which is the calendar time expressed for some specific time zone, and with Daylight
Saving Time, which is a temporary change in the algorithm for determining local time.
The local time zone and Daylight Saving Time are implementation-defined.

2

The macros defined are NULL (described in 7.17); andCLOCKS_PER_SEC
which expands to an expression with type clock_t (described below) that is thenumber per second of the value returned by the clock function.

3

The types declared are size_t (described in 7.17);
clock_tandtime_twhich are arithmetic types capable of representing times; andstruct tm
which holds the components of a calendar time, called the broken-down time.

4

The range and precision of times representable in clock_t and time_t are
implementation-defined. The tm structure shall contain at least the following members,in any order. The semantics of the members and their normal ranges are expressed in thecomments.274)
int tm_sec;// seconds after the minute — [0, 60]
int tm_min;// minutes after the hour — [0, 59]
int tm_hour; // hours since midnight — [0, 23]
int tm_mday; // day of the month — [1, 31]
int tm_mon;// months since January — [0, 11]
int tm_year; // years since 1900
int tm_wday; // days since Sunday — [0, 6]
int tm_yday; // days since January 1 — [0, 365]
int tm_isdst; // Daylight Saving Time flag274) The range [0, 60] for tm_sec allows for a positive leap second.

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The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
Saving Time is not in effect, and negative if the information is not available.

7.23.2 Time manipulation functions
7.23.2.1 The clock function
Synopsis1#include <time.h>clock_t clock(void);
Description

2

The clock function determines the processor time used.
Returns3

The clock function returns the implementation’s best approximation to the processor
time used by the program since the beginning of an implementation-defined era related
only to the program invocation. To determine the time in seconds, the value returned by
the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
the processor time used is not available or its value cannot be represented, the function
returns the value (clock_t)(-1).275)

7.23.2.2 The difftime function
Synopsis1#include <time.h>double difftime(time_t time1, time_t time0);
Description

2

The difftime function computes the difference between two calendar times: time1 time0.
Returns3

The difftime function returns the difference expressed in seconds as a double.

275) In order to measure the time spent in a program, the clock function should be called at the start ofthe program and its return value subtracted from the value returned by subsequent calls.

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7.23.2.3 The mktime function
Synopsis1#include <time.h>
time_t mktime(struct tm *timeptr);
Description

2

The mktime function converts the broken-down time, expressed as local time, in the
structure pointed to by timeptr into a calendar time value with the same encoding asthat of the values returned by the time function. The original values of the tm_wday
and tm_yday components of the structure are ignored, and the original values of theother components are not restricted to the ranges indicated above.276) On successful
completion, the values of the tm_wday and tm_yday components of the structure are
set appropriately, and the other components are set to represent the specified calendar
time, but with their values forced to the ranges indicated above; the final value of
tm_mday is not set until tm_mon and tm_year are determined.
Returns3

The mktime function returns the specified calendar time encoded as a value of type
time_t. If the calendar time cannot be represented, the function returns the value(time_t)(-1).

4EXAMPLE

What day of the week is July 4, 2001?

#include <stdio.h>#include <time.h>static const char *const wday[] = {"Sunday", "Monday", "Tuesday", "Wednesday","Thursday", "Friday", "Saturday", "-unknown-"};
struct tm time_str;/* ... */276) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative valuecauses it to attempt to determine whether Daylight Saving Time is in effect for the specified time.

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time_str.tm_year= 2001 - 1900;
time_str.tm_mon= 7 - 1;
time_str.tm_mday= 4;
time_str.tm_hour= 0;time_str.tm_min= 0;time_str.tm_sec= 1;
time_str.tm_isdst = -1;
if (mktime(&time_str) == (time_t)(-1))
time_str.tm_wday = 7;
printf("%s\n", wday[time_str.tm_wday]);

7.23.2.4 The time function
Synopsis1#include <time.h>
time_t time(time_t *timer);
Description

2

The time function determines the current calendar time. The encoding of the value isunspecified.
Returns

3

The time function returns the implementation’s best approximation to the current
calendar time. The value (time_t)(-1) is returned if the calendar time is notavailable. If timer is not a null pointer, the return value is also assigned to the object it
points to.

7.23.3 Time conversion functions
1

Except for the strftime function, these functions each return a pointer to one of two
types of static objects: a broken-down time structure or an array of char. Execution of
any of the functions that return a pointer to one of these object types may overwrite theinformation in any object of the same type pointed to by the value returned from any
previous call to any of them. The implementation shall behave as if no other libraryfunctions call these functions.

7.23.3.1 The asctime function
Synopsis1#include <time.h>char *asctime(const struct tm *timeptr);
Description

2

The asctime function converts the broken-down time in the structure pointed to by
timeptr into a string in the form
Sun Sep 16 01:03:52 1973\n\0§7.23.3.1

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using the equivalent of the following algorithm.
char *asctime(const struct tm *timeptr){
static const char wday_name[7][3] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};static const char mon_name[12][3] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun","Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};static char result[26];sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",wday_name[timeptr->tm_wday],mon_name[timeptr->tm_mon],timeptr->tm_mday, timeptr->tm_hour,
timeptr->tm_min, timeptr->tm_sec,
1900 + timeptr->tm_year);
return result;}
Returns3

The asctime function returns a pointer to the string.

7.23.3.2 The ctime function
Synopsis1#include <time.h>char *ctime(const time_t *timer);
Description

2

The ctime function converts the calendar time pointed to by timer to local time in theform of a string. It is equivalent toasctime(localtime(timer))
Returns3

The ctime function returns the pointer returned by the asctime function with thatbroken-down time as argument.
Forward references: the localtime function (7.23.3.4).

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7.23.3.3 The gmtime function
Synopsis1#include <time.h>
struct tm *gmtime(const time_t *timer);
Description

2

The gmtime function converts the calendar time pointed to by timer into a brokendown time, expressed as UTC.
Returns

3

The gmtime function returns a pointer to the broken-down time, or a null pointer if thespecified time cannot be converted to UTC.

7.23.3.4 The localtime function
Synopsis1#include <time.h>
struct tm *localtime(const time_t *timer);
Description

2

The localtime function converts the calendar time pointed to by timer into a
broken-down time, expressed as local time.
Returns3

The localtime function returns a pointer to the broken-down time, or a null pointer if
the specified time cannot be converted to local time.

7.23.3.5 The strftime function
Synopsis1#include <time.h>size_t strftime(char * restrict s,size_t maxsize,
const char * restrict format,
const struct tm * restrict timeptr);
Description

2

The strftime function places characters into the array pointed to by s as controlled by
the string pointed to by format. The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format string consists of zero or
more conversion specifiers and ordinary multibyte characters. A conversion specifierconsists of a % character, possibly followed by an E or O modifier character (described
below), followed by a character that determines the behavior of the conversion specifier.
All ordinary multibyte characters (including the terminating null character) are copied§7.23.3.5
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unchanged into the array. If copying takes place between objects that overlap, thebehavior is undefined. No more than maxsize characters are placed into the array.
3

Each conversion specifier is replaced by appropriate characters as described in thefollowing list. The appropriate characters are determined using the LC_TIME categoryof the current locale and by the values of zero or more members of the broken-down time
structure pointed to by timeptr, as specified in brackets in the description. If any of
the specified values is outside the normal range, the characters stored are unspecified.
%a
%A
%b
%B
%c
%C
%d
%D
%e
%F
%g
%G
%h
%H
%I
%j
%m
%M
%n
%p
%r
%R
%S
%t
%T

344

is replaced by the locale’s abbreviated weekday name. [tm_wday]
is replaced by the locale’s full weekday name. [tm_wday]
is replaced by the locale’s abbreviated month name. [tm_mon]is replaced by the locale’s full month name. [tm_mon]is replaced by the locale’s appropriate date and time representation. [all specified
in 7.23.1]
is replaced by the year divided by 100 and truncated to an integer, as a decimal
number (00−99). [tm_year]
is replaced by the day of the month as a decimal number (01−31). [tm_mday]
is equivalent to ‘‘%m/%d/%y’’. [tm_mon, tm_mday, tm_year]
is replaced by the day of the month as a decimal number (1−31); a single digit ispreceded by a space. [tm_mday]
is equivalent to ‘‘%Y−%m−%d’’ (the ISO 8601 date format). [tm_year, tm_mon,tm_mday]
is replaced by the last 2 digits of the week-based year (see below) as a decimal
number (00−99). [tm_year, tm_wday, tm_yday]
is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
[tm_year, tm_wday, tm_yday]
is equivalent to ‘‘%b’’. [tm_mon]is replaced by the hour (24-hour clock) as a decimal number (00−23). [tm_hour]is replaced by the hour (12-hour clock) as a decimal number (01−12). [tm_hour]is replaced by the day of the year as a decimal number (001−366). [tm_yday]
is replaced by the month as a decimal number (01−12). [tm_mon]is replaced by the minute as a decimal number (00−59). [tm_min]is replaced by a new-line character.
is replaced by the locale’s equivalent of the AM/PM designations associated with a
12-hour clock. [tm_hour]is replaced by the locale’s 12-hour clock time. [tm_hour, tm_min, tm_sec]
is equivalent to ‘‘%H:%M’’. [tm_hour, tm_min]is replaced by the second as a decimal number (00−60). [tm_sec]
is replaced by a horizontal-tab character.
is equivalent to ‘‘%H:%M:%S’’ (the ISO 8601 time format). [tm_hour, tm_min,tm_sec]Library§7.23.3.5

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%u
%U
%V
%w
%W
%x
%X
%y
%Y
%z

%Z
%%
4

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is replaced by the ISO 8601 weekday as a decimal number (1−7), where Monday
is 1. [tm_wday]
is replaced by the week number of the year (the first Sunday as the first day of week1) as a decimal number (00−53). [tm_year, tm_wday, tm_yday]
is replaced by the ISO 8601 week number (see below) as a decimal number(01−53). [tm_year, tm_wday, tm_yday]
is replaced by the weekday as a decimal number (0−6), where Sunday is 0.
[tm_wday]is replaced by the week number of the year (the first Monday as the first day ofweek 1) as a decimal number (00−53). [tm_year, tm_wday, tm_yday]
is replaced by the locale’s appropriate date representation. [all specified in 7.23.1]
is replaced by the locale’s appropriate time representation. [all specified in 7.23.1]
is replaced by the last 2 digits of the year as a decimal number (00−99).
[tm_year]is replaced by the year as a decimal number (e.g., 1997). [tm_year]
is replaced by the offset from UTC in the ISO 8601 format ‘‘−0430’’ (meaning 4
hours 30 minutes behind UTC, west of Greenwich), or by no characters if no timezone is determinable. [tm_isdst]
is replaced by the locale’s time zone name or abbreviation, or by no characters if notime zone is determinable. [tm_isdst]
is replaced by %.

Some conversion specifiers can be modified by the inclusion of an E or O modifiercharacter to indicate an alternative format or specification. If the alternative format or
specification does not exist for the current locale, the modifier is ignored.
%Ec is replaced by the locale’s alternative date and time representation.
%EC is replaced by the name of the base year (period) in the locale’s alternative
representation.
%Ex is replaced by the locale’s alternative date representation.
%EX is replaced by the locale’s alternative time representation.
%Ey is replaced by the offset from %EC (year only) in the locale’s alternative
representation.
%EY is replaced by the locale’s full alternative year representation.
%Od is replaced by the day of the month, using the locale’s alternative numeric symbols(filled as needed with leading zeros, or with leading spaces if there is no alternative
symbol for zero).
%Oe is replaced by the day of the month, using the locale’s alternative numeric symbols(filled as needed with leading spaces).
%OH is replaced by the hour (24-hour clock), using the locale’s alternative numericsymbols.

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%Om is replaced by the month, using the locale’s alternative numeric symbols.
%OM is replaced by the minutes, using the locale’s alternative numeric symbols.
%OS is replaced by the seconds, using the locale’s alternative numeric symbols.
%Ou is replaced by the ISO 8601 weekday as a number in the locale’s alternative
representation, where Monday is 1.
%OU is replaced by the week number, using the locale’s alternative numeric symbols.
%OV is replaced by the ISO 8601 week number, using the locale’s alternative numericsymbols.
%Ow is replaced by the weekday as a number, using the locale’s alternative numericsymbols.
%OW is replaced by the week number of the year, using the locale’s alternative numericsymbols.
%Oy is replaced by the last 2 digits of the year, using the locale’s alternative numericsymbols.
5%g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
which is also the week that includes the first Thursday of the year, and is also the firstweek that contains at least four days in the year. If the first Monday of January is the
2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and%V is replaced by 01.

6

If a conversion specifier is not one of the above, the behavior is undefined.

7

In the "C" locale, the E and O modifiers are ignored and the replacement strings for thefollowing specifiers are:
%a
%A
%b
%B
%c
%p
%r
%x
%X
%Z

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the first three characters of %A.
one of ‘‘Sunday’’, ‘‘Monday’’, ... , ‘‘Saturday’’.
the first three characters of %B.
one of ‘‘January’’, ‘‘February’’, ... , ‘‘December’’.
equivalent to ‘‘%a %b %e %T %Y’’.
one of ‘‘AM’’ or ‘‘PM’’.
equivalent to ‘‘%I:%M:%S %p’’.
equivalent to ‘‘%m/%d/%y’’.
equivalent to %T.
implementation-defined.

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Returns8

If the total number of resulting characters including the terminating null character is not
more than maxsize, the strftime function returns the number of characters placed
into the array pointed to by s not including the terminating null character. Otherwise,
zero is returned and the contents of the array are indeterminate.

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7.24 Extended multibyte and wide character utilities <wchar.h>
7.24.1 Introduction
1

The header <wchar.h> declares four data types, one tag, four macros, and many
functions.277)

2

The types declared are wchar_t and size_t (both described in 7.17);
mbstate_t
which is an object type other than an array type that can hold the conversion state
information necessary to convert between sequences of multibyte characters and wide
characters;
wint_twhich is an integer type unchanged by default argument promotions that can hold any
value corresponding to members of the extended character set, as well as at least one
value that does not correspond to any member of the extended character set (see WEOF
below);278) andstruct tm
which is declared as an incomplete structure type (the contents are described in 7.23.1).

3

The macros defined are NULL (described in 7.17); WCHAR_MIN and WCHAR_MAX(described in 7.18.3); andWEOF
which expands to a constant expression of type wint_t whose value does notcorrespond to any member of the extended character set.279) It is accepted (and returned)
by several functions in this subclause to indicate end-of-file, that is, no more input from astream. It is also used as a wide character value that does not correspond to any memberof the extended character set.

4

The functions declared are grouped as follows:— Functions that perform input and output of wide characters, or multibyte characters,
or both;— Functions that provide wide string numeric conversion;— Functions that perform general wide string manipulation;277) See ‘‘future library directions’’ (7.26.12).
278) wchar_t and wint_t can be the same integer type.
279) The value of the macro WEOF may differ from that of EOF and need not be negative.

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ISO/IEC 9899:TC3— Functions for wide string date and time conversion; and— Functions that provide extended capabilities for conversion between multibyte andwide character sequences.
5

Unless explicitly stated otherwise, if the execution of a function described in thissubclause causes copying to take place between objects that overlap, the behavior isundefined.

7.24.2 Formatted wide character input/output functions
1

The formatted wide character input/output functions shall behave as if there is a sequence
point after the actions associated with each specifier.280)

7.24.2.1 The fwprintf function
Synopsis1#include <stdio.h>#include <wchar.h>
int fwprintf(FILE * restrict stream,
const wchar_t * restrict format, ...);
Description

2

The fwprintf function writes output to the stream pointed to by stream, undercontrol of the wide string pointed to by format that specifies how subsequent arguments
are converted for output. If there are insufficient arguments for the format, the behavior
is undefined. If the format is exhausted while arguments remain, the excess arguments
are evaluated (as always) but are otherwise ignored. The fwprintf function returns
when the end of the format string is encountered.

3

The format is composed of zero or more directives: ordinary wide characters (not %),which are copied unchanged to the output stream; and conversion specifications, each ofwhich results in fetching zero or more subsequent arguments, converting them, if
applicable, according to the corresponding conversion specifier, and then writing theresult to the output stream.

4

Each conversion specification is introduced by the wide character %. After the %, thefollowing appear in sequence:— Zero or more flags (in any order) that modify the meaning of the conversion
specification.
— An optional minimum field width. If the converted value has fewer wide charactersthan the field width, it is padded with spaces (by default) on the left (or right, if the280) The fwprintf functions perform writes to memory for the %n specifier.

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left adjustment flag, described later, has been given) to the field width. The field
width takes the form of an asterisk * (described later) or a nonnegative decimal
integer.281)— An optional precision that gives the minimum number of digits to appear for the d, i,o, u, x, and X conversions, the number of digits to appear after the decimal-point
wide character for a, A, e, E, f, and F conversions, the maximum number ofsignificant digits for the g and G conversions, or the maximum number of wide
characters to be written for s conversions. The precision takes the form of a period(.) followed either by an asterisk * (described later) or by an optional decimal
integer; if only the period is specified, the precision is taken as zero. If a precisionappears with any other conversion specifier, the behavior is undefined.
— An optional length modifier that specifies the size of the argument.
— A conversion specifier wide character that specifies the type of conversion to be
applied.
5

As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
this case, an int argument supplies the field width or precision. The arguments
specifying field width, or precision, or both, shall appear (in that order) before theargument (if any) to be converted. A negative field width argument is taken as a - flag
followed by a positive field width. A negative precision argument is taken as if the
precision were omitted.

6

The flag wide characters and their meanings are:-

The result of the conversion is left-justified within the field. (It is right-justified if
this flag is not specified.)+

The result of a signed conversion always begins with a plus or minus sign. (Itbegins with a sign only when a negative value is converted if this flag is not
specified.)282)

space If the first wide character of a signed conversion is not a sign, or if a signed
conversion results in no wide characters, a space is prefixed to the result. If thespace and + flags both appear, the space flag is ignored.
#

The result is converted to an ‘‘alternative form’’. For o conversion, it increases
the precision, if and only if necessary, to force the first digit of the result to be azero (if the value and precision are both 0, a single 0 is printed). For x (or X)
conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,281) Note that 0 is taken as a flag, not as the beginning of a field width.
282) The results of all floating conversions of a negative zero, and of negative values that round to zero,include a minus sign.

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and G conversions, the result of converting a floating-point number always
contains a decimal-point wide character, even if no digits follow it. (Normally, adecimal-point wide character appears in the result of these conversions only if adigit follows it.) For g and G conversions, trailing zeros are not removed from theresult. For other conversions, the behavior is undefined.
07

For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros(following any indication of sign or base) are used to pad to the field width rather
than performing space padding, except when converting an infinity or NaN. If the
0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
conversions, if a precision is specified, the 0 flag is ignored. For otherconversions, the behavior is undefined.

The length modifiers and their meanings are:hhSpecifies that a following d, i, o, u, x, or X conversion specifier applies to asigned char or unsigned char argument (the argument will havebeen promoted according to the integer promotions, but its value shall be
converted to signed char or unsigned char before printing); or thata following n conversion specifier applies to a pointer to a signed charargument.

hSpecifies that a following d, i, o, u, x, or X conversion specifier applies to ashort int or unsigned short int argument (the argument will
have been promoted according to the integer promotions, but its value shallbe converted to short int or unsigned short int before printing);or that a following n conversion specifier applies to a pointer to a short
int argument.

l (ell)Specifies that a following d, i, o, u, x, or X conversion specifier applies to along int or unsigned long int argument; that a following nconversion specifier applies to a pointer to a long int argument; that afollowing c conversion specifier applies to a wint_t argument; that afollowing s conversion specifier applies to a pointer to a wchar_t
argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
specifier.

ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to along long int or unsigned long long int argument; or that afollowing n conversion specifier applies to a pointer to a long long int
argument.
j§7.24.2.1

Specifies that a following d, i, o, u, x, or X conversion specifier applies toan intmax_t or uintmax_t argument; or that a following n conversion
specifier applies to a pointer to an intmax_t argument.
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z

Specifies that a following d, i, o, u, x, or X conversion specifier applies to asize_t or the corresponding signed integer type argument; or that afollowing n conversion specifier applies to a pointer to a signed integer typecorresponding to size_t argument.

tSpecifies that a following d, i, o, u, x, or X conversion specifier applies to a
ptrdiff_t or the corresponding unsigned integer type argument; or that afollowing n conversion specifier applies to a pointer to a ptrdiff_t
argument.

LSpecifies that a following a, A, e, E, f, F, g, or G conversion specifier
applies to a long double argument.

If a length modifier appears with any conversion specifier other than as specified above,
the behavior is undefined.
8

The conversion specifiers and their meanings are:d,i

The int argument is converted to signed decimal in the style [−]dddd. The
precision specifies the minimum number of digits to appear; if the value
being converted can be represented in fewer digits, it is expanded withleading zeros. The default precision is 1. The result of converting a zero
value with a precision of zero is no wide characters.

o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; theletters abcdef are used for x conversion and the letters ABCDEF for X
conversion. The precision specifies the minimum number of digits to appear;
if the value being converted can be represented in fewer digits, it is expandedwith leading zeros. The default precision is 1. The result of converting azero value with a precision of zero is no wide characters.
f,FA double argument representing a floating-point number is converted todecimal notation in the style [−]ddd.ddd, where the number of digits after
the decimal-point wide character is equal to the precision specification. If the
precision is missing, it is taken as 6; if the precision is zero and the # flag is
not specified, no decimal-point wide character appears. If a decimal-point
wide character appears, at least one digit appears before it. The value isrounded to the appropriate number of digits.
A double argument representing an infinity is converted in one of the styles[-]inf or [-]infinity — which style is implementation-defined. A
double argument representing a NaN is converted in one of the styles[-]nan or [-]nan(n-wchar-sequence) — which style, and the meaning of
any n-wchar-sequence, is implementation-defined. The F conversion
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nan, respectively.283)
e,E

A double argument representing a floating-point number is converted in thestyle [−]d.ddd e±dd, where there is one digit (which is nonzero if theargument is nonzero) before the decimal-point wide character and the numberof digits after it is equal to the precision; if the precision is missing, it is taken
as 6; if the precision is zero and the # flag is not specified, no decimal-point
wide character appears. The value is rounded to the appropriate number ofdigits. The E conversion specifier produces a number with E instead of e
introducing the exponent. The exponent always contains at least two digits,
and only as many more digits as necessary to represent the exponent. If thevalue is zero, the exponent is zero.
A double argument representing an infinity or NaN is converted in the styleof an f or F conversion specifier.

g,GA double argument representing a floating-point number is converted instyle f or e (or in style F or E in the case of a G conversion specifier),
depending on the value converted and the precision. Let P equal the
precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
Then, if a conversion with style E would have an exponent of X :— if P > X ≥ −4, the conversion is with style f (or F) and precisionP − (X + 1).

— otherwise, the conversion is with style e (or E) and precision P − 1.

Finally, unless the # flag is used, any trailing zeros are removed from thefractional portion of the result and the decimal-point wide character isremoved if there is no fractional portion remaining.

A double argument representing an infinity or NaN is converted in the styleof an f or F conversion specifier.
a,AA double argument representing a floating-point number is converted in thestyle [−]0xh.hhhh p±d, where there is one hexadecimal digit (which isnonzero if the argument is a normalized floating-point number and isotherwise unspecified) before the decimal-point wide character284) and thenumber of hexadecimal digits after it is equal to the precision; if the precision
is missing and FLT_RADIX is a power of 2, then the precision is sufficient283) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
meaning; the # and 0 flag wide characters have no effect.
284) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
character so that subsequent digits align to nibble (4-bit) boundaries.

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for an exact representation of the value; if the precision is missing and
FLT_RADIX is not a power of 2, then the precision is sufficient todistinguish285) values of type double, except that trailing zeros may beomitted; if the precision is zero and the # flag is not specified, no decimalpoint wide character appears. The letters abcdef are used for a conversion
and the letters ABCDEF for A conversion. The A conversion specifier
produces a number with X and P instead of x and p. The exponent always
contains at least one digit, and only as many more digits as necessary torepresent the decimal exponent of 2. If the value is zero, the exponent iszero.
A double argument representing an infinity or NaN is converted in the styleof an f or F conversion specifier.
c

If no l length modifier is present, the int argument is converted to a wide
character as if by calling btowc and the resulting wide character is written.
If an l length modifier is present, the wint_t argument is converted towchar_t and written.

s

If no l length modifier is present, the argument shall be a pointer to the initial
element of a character array containing a multibyte character sequence
beginning in the initial shift state. Characters from the array are converted as
if by repeated calls to the mbrtowc function, with the conversion state
described by an mbstate_t object initialized to zero before the firstmultibyte character is converted, and written up to (but not including) the
terminating null wide character. If the precision is specified, no more thanthat many wide characters are written. If the precision is not specified or isgreater than the size of the converted array, the converted array shall contain anull wide character.
If an l length modifier is present, the argument shall be a pointer to the initial
element of an array of wchar_t type. Wide characters from the array are
written up to (but not including) a terminating null wide character. If the
precision is specified, no more than that many wide characters are written. If
the precision is not specified or is greater than the size of the array, the array
shall contain a null wide character.

p

The argument shall be a pointer to void. The value of the pointer isconverted to a sequence of printing wide characters, in an implementation-285) The precision p is sufficient to distinguish values of the source type if 16 p−1 > b n where b is
FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller pmight suffice depending on the implementation’s scheme for determining the digit to the left of thedecimal-point wide character.

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defined manner.
n

The argument shall be a pointer to signed integer into which is written thenumber of wide characters written to the output stream so far by this call to
fwprintf. No argument is converted, but one is consumed. If theconversion specification includes any flags, a field width, or a precision, thebehavior is undefined.

%

A % wide character is written. No argument is converted. The complete
conversion specification shall be %%.

9

If a conversion specification is invalid, the behavior is undefined.286) If any argument is
not the correct type for the corresponding conversion specification, the behavior isundefined.

10

In no case does a nonexistent or small field width cause truncation of a field; if the resultof a conversion is wider than the field width, the field is expanded to contain theconversion result.

11

For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
to a hexadecimal floating number with the given precision.
Recommended practice12

For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
representable in the given precision, the result should be one of the two adjacent numbers
in hexadecimal floating style with the given precision, with the extra stipulation that theerror should have a correct sign for the current rounding direction.

13

For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
DECIMAL_DIG, then the result should be correctly rounded.287) If the number ofsignificant decimal digits is more than DECIMAL_DIG but the source value is exactly
representable with DECIMAL_DIG digits, then the result should be an exact
representation with trailing zeros. Otherwise, the source value is bounded by two
adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the valueof the resultant decimal string D should satisfy L ≤ D ≤ U, with the extra stipulation thatthe error should have a correct sign for the current rounding direction.
Returns

14

The fwprintf function returns the number of wide characters transmitted, or a negativevalue if an output or encoding error occurred.
286) See ‘‘future library directions’’ (7.26.12).
287) For binary-to-decimal conversion, the result format’s values are the numbers representable with thegiven format specifier. The number of significant digits is determined by the format specifier, and in
the case of fixed-point conversion by the source value as well.

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Environmental limits
15

The number of wide characters that can be produced by any single conversion shall be atleast 4095.

16

EXAMPLE
places:To print a date and time in the form ‘‘Sunday, July 3, 10:02’’ followed by π to five decimal#include <math.h>#include <stdio.h>#include <wchar.h>/* ... */wchar_t *weekday, *month; // pointers to wide strings
int day, hour, min;fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",weekday, month, day, hour, min);fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));

Forward references:(7.24.6.3.2).

the btowc function (7.24.6.1.1), the mbrtowc function

7.24.2.2 The fwscanf function
Synopsis1#include <stdio.h>#include <wchar.h>
int fwscanf(FILE * restrict stream,
const wchar_t * restrict format, ...);
Description

2

The fwscanf function reads input from the stream pointed to by stream, undercontrol of the wide string pointed to by format that specifies the admissible input
sequences and how they are to be converted for assignment, using subsequent arguments
as pointers to the objects to receive the converted input. If there are insufficientarguments for the format, the behavior is undefined. If the format is exhausted whilearguments remain, the excess arguments are evaluated (as always) but are otherwise
ignored.

3

The format is composed of zero or more directives: one or more white-space wide
characters, an ordinary wide character (neither % nor a white-space wide character), or aconversion specification. Each conversion specification is introduced by the wide
character %. After the %, the following appear in sequence:— An optional assignment-suppressing wide character *.
— An optional decimal integer greater than zero that specifies the maximum field width(in wide characters).

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ISO/IEC 9899:TC3— An optional length modifier that specifies the size of the receiving object.
— A conversion specifier wide character that specifies the type of conversion to be
applied.
4

The fwscanf function executes each directive of the format in turn. If a directive fails,
as detailed below, the function returns. Failures are described as input failures (due to theoccurrence of an encoding error or the unavailability of input characters), or matching
failures (due to inappropriate input).

5

A directive composed of white-space wide character(s) is executed by reading input up to
the first non-white-space wide character (which remains unread), or until no more wide
characters can be read.

6

A directive that is an ordinary wide character is executed by reading the next wide
character of the stream. If that wide character differs from the directive, the directive
fails and the differing and subsequent wide characters remain unread. Similarly, if endof-file, an encoding error, or a read error prevents a wide character from being read, thedirective fails.

7

A directive that is a conversion specification defines a set of matching input sequences, as
described below for each specifier. A conversion specification is executed in thefollowing steps:

8

Input white-space wide characters (as specified by the iswspace function) are skipped,
unless the specification includes a [, c, or n specifier.288)

9

An input item is read from the stream, unless the specification includes an n specifier. An
input item is defined as the longest sequence of input wide characters which does notexceed any specified field width and which is, or is a prefix of, a matching input
sequence.289) The first wide character, if any, after the input item remains unread. If thelength of the input item is zero, the execution of the directive fails; this condition is amatching failure unless end-of-file, an encoding error, or a read error prevented input
from the stream, in which case it is an input failure.

10

Except in the case of a % specifier, the input item (or, in the case of a %n directive, thecount of input wide characters) is converted to a type appropriate to the conversion
specifier. If the input item is not a matching sequence, the execution of the directive fails:
this condition is a matching failure. Unless assignment suppression was indicated by a *,the result of the conversion is placed in the object pointed to by the first argument
following the format argument that has not already received a conversion result. If this288) These white-space wide characters are not counted against a specified field width.
289) fwscanf pushes back at most one input wide character onto the input stream. Therefore, somesequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.

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object does not have an appropriate type, or if the result of the conversion cannot be
represented in the object, the behavior is undefined.
11

The length modifiers and their meanings are:hhSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to signed char or unsigned char.

hSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to short int or unsigned shortint.

l (ell)Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to long int or unsigned longint; that a following a, A, e, E, f, F, g, or G conversion specifier applies toan argument with type pointer to double; or that a following c, s, or [conversion specifier applies to an argument with type pointer to wchar_t.

ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to long long int or unsigned
long long int.
jSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to intmax_t or uintmax_t.

zSpecifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to size_t or the corresponding signed
integer type.

t

Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
to an argument with type pointer to ptrdiff_t or the corresponding
unsigned integer type.

L

Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
applies to an argument with type pointer to long double.

If a length modifier appears with any conversion specifier other than as specified above,
the behavior is undefined.
12

The conversion specifiers and their meanings are:dMatches an optionally signed decimal integer, whose format is the same as
expected for the subject sequence of the wcstol function with the value 10
for the base argument. The corresponding argument shall be a pointer tosigned integer.

iMatches an optionally signed integer, whose format is the same as expected
for the subject sequence of the wcstol function with the value 0 for thebase argument. The corresponding argument shall be a pointer to signed

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integer.
oMatches an optionally signed octal integer, whose format is the same as
expected for the subject sequence of the wcstoul function with the value 8
for the base argument. The corresponding argument shall be a pointer tounsigned integer.

uMatches an optionally signed decimal integer, whose format is the same as
expected for the subject sequence of the wcstoul function with the value 10
for the base argument. The corresponding argument shall be a pointer tounsigned integer.

xMatches an optionally signed hexadecimal integer, whose format is the same
as expected for the subject sequence of the wcstoul function with the value
16 for the base argument. The corresponding argument shall be a pointer tounsigned integer.

a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
format is the same as expected for the subject sequence of the wcstod
function. The corresponding argument shall be a pointer to floating.
cMatches a sequence of wide characters of exactly the number specified by thefield width (1 if no field width is present in the directive).
If no l length modifier is present, characters from the input field areconverted as if by repeated calls to the wcrtomb function, with theconversion state described by an mbstate_t object initialized to zero
before the first wide character is converted. The corresponding argument
shall be a pointer to the initial element of a character array large enough toaccept the sequence. No null character is added.
If an l length modifier is present, the corresponding argument shall be apointer to the initial element of an array of wchar_t large enough to accept
the sequence. No null wide character is added.

sMatches a sequence of non-white-space wide characters.
If no l length modifier is present, characters from the input field areconverted as if by repeated calls to the wcrtomb function, with theconversion state described by an mbstate_t object initialized to zero
before the first wide character is converted. The corresponding argument
shall be a pointer to the initial element of a character array large enough toaccept the sequence and a terminating null character, which will be added
automatically.
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the sequence and the terminating null wide character, which will be added
automatically.
[

Matches a nonempty sequence of wide characters from a set of expectedcharacters (the scanset).
If no l length modifier is present, characters from the input field areconverted as if by repeated calls to the wcrtomb function, with theconversion state described by an mbstate_t object initialized to zero
before the first wide character is converted. The corresponding argument
shall be a pointer to the initial element of a character array large enough toaccept the sequence and a terminating null character, which will be added
automatically.
If an l length modifier is present, the corresponding argument shall be apointer to the initial element of an array of wchar_t large enough to accept
the sequence and the terminating null wide character, which will be added
automatically.
The conversion specifier includes all subsequent wide characters in theformat string, up to and including the matching right bracket (]). The wide
characters between the brackets (the scanlist) compose the scanset, unless thewide character after the left bracket is a circumflex (^), in which case thescanset contains all wide characters that do not appear in the scanlist between
the circumflex and the right bracket. If the conversion specifier begins with[] or [^], the right bracket wide character is in the scanlist and the next
following right bracket wide character is the matching right bracket that ends
the specification; otherwise the first following right bracket wide character isthe one that ends the specification. If a - wide character is in the scanlist andis not the first, nor the second where the first wide character is a ^, nor thelast character, the behavior is implementation-defined.

pMatches an implementation-defined set of sequences, which should be thesame as the set of sequences that may be produced by the %p conversion of
the fwprintf function. The corresponding argument shall be a pointer to apointer to void. The input item is converted to a pointer value in an
implementation-defined manner. If the input item is a value converted earlier
during the same program execution, the pointer that results shall compare
equal to that value; otherwise the behavior of the %p conversion is undefined.

n

No input is consumed. The corresponding argument shall be a pointer tosigned integer into which is to be written the number of wide characters readfrom the input stream so far by this call to the fwscanf function. Executionof a %n directive does not increment the assignment count returned at thecompletion of execution of the fwscanf function. No argument is

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converted, but one is consumed. If the conversion specification includes anassignment-suppressing wide character or a field width, the behavior isundefined.
Matches a single % wide character; no conversion or assignment occurs. The
complete conversion specification shall be %%.

%13

If a conversion specification is invalid, the behavior is undefined.290)

14

The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
respectively, a, e, f, g, and x.

15

Trailing white space (including new-line wide characters) is left unread unless matchedby a directive. The success of literal matches and suppressed assignments is not directly
determinable other than via the %n directive.
Returns

16

The fwscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the function returns the number of input items
assigned, which can be fewer than provided for, or even zero, in the event of an earlymatching failure.

17

EXAMPLE 1

The call:#include <stdio.h>#include <wchar.h>/* ... */int n, i; float x; wchar_t name[50];n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);with the input line:
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
thompson\0.

18

EXAMPLE 2

The call:#include <stdio.h>#include <wchar.h>/* ... */int i; float x; double y;
fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);with input:
56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value
56.0. The next wide character read from the input stream will be a.

290) See ‘‘future library directions’’ (7.26.12).

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Forward references: the wcstod, wcstof, and wcstold functions (7.24.4.1.1), thewcstol, wcstoll, wcstoul, and wcstoull functions (7.24.4.1.2), the wcrtomb
function (7.24.6.3.3).

7.24.2.3 The swprintf function
Synopsis1#include <wchar.h>
int swprintf(wchar_t * restrict s,size_t n,
const wchar_t * restrict format, ...);
Description

2

The swprintf function is equivalent to fwprintf, except that the argument s
specifies an array of wide characters into which the generated output is to be written,
rather than written to a stream. No more than n wide characters are written, including aterminating null wide character, which is always added (unless n is zero).
Returns

3

The swprintf function returns the number of wide characters written in the array, notcounting the terminating null wide character, or a negative value if an encoding error
occurred or if n or more wide characters were requested to be written.

7.24.2.4 The swscanf function
Synopsis1#include <wchar.h>
int swscanf(const wchar_t * restrict s,
const wchar_t * restrict format, ...);
Description

2

The swscanf function is equivalent to fwscanf, except that the argument s specifies awide string from which the input is to be obtained, rather than from a stream. Reaching
the end of the wide string is equivalent to encountering end-of-file for the fwscanffunction.
Returns

3

The swscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the swscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

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7.24.2.5 The vfwprintf function
Synopsis1#include <stdarg.h>#include <stdio.h>#include <wchar.h>
int vfwprintf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description

2

The vfwprintf function is equivalent to fwprintf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vfwprintf function does not invoke theva_end macro.291)
Returns3

The vfwprintf function returns the number of wide characters transmitted, or anegative value if an output or encoding error occurred.

4

EXAMPLEroutine.

The following shows the use of the vfwprintf function in a general error-reporting#include <stdarg.h>#include <stdio.h>#include <wchar.h>void error(char *function_name, wchar_t *format, ...){
va_list args;
va_start(args, format);// print out name of function causing error
fwprintf(stderr, L"ERROR in %s: ", function_name);// print out remainder of message
vfwprintf(stderr, format, args);
va_end(args);}291) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
invoke the va_arg macro, the value of arg after the return is indeterminate.

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7.24.2.6 The vfwscanf function
Synopsis1#include <stdarg.h>#include <stdio.h>#include <wchar.h>
int vfwscanf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description

2

The vfwscanf function is equivalent to fwscanf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vfwscanf function does not invoke theva_end macro.291)
Returns3

The vfwscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the vfwscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

7.24.2.7 The vswprintf function
Synopsis1#include <stdarg.h>#include <wchar.h>
int vswprintf(wchar_t * restrict s,size_t n,
const wchar_t * restrict format,
va_list arg);
Description

2

The vswprintf function is equivalent to swprintf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vswprintf function does not invoke theva_end macro.291)
Returns3

The vswprintf function returns the number of wide characters written in the array, notcounting the terminating null wide character, or a negative value if an encoding error
occurred or if n or more wide characters were requested to be generated.

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7.24.2.8 The vswscanf function
Synopsis1#include <stdarg.h>#include <wchar.h>
int vswscanf(const wchar_t * restrict s,
const wchar_t * restrict format,
va_list arg);
Description

2

The vswscanf function is equivalent to swscanf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vswscanf function does not invoke theva_end macro.291)
Returns3

The vswscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the vswscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

7.24.2.9 The vwprintf function
Synopsis1#include <stdarg.h>#include <wchar.h>
int vwprintf(const wchar_t * restrict format,
va_list arg);
Description

2

The vwprintf function is equivalent to wprintf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vwprintf function does not invoke theva_end macro.291)
Returns3

The vwprintf function returns the number of wide characters transmitted, or a negativevalue if an output or encoding error occurred.

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7.24.2.10 The vwscanf function
Synopsis1#include <stdarg.h>#include <wchar.h>
int vwscanf(const wchar_t * restrict format,
va_list arg);
Description

2

The vwscanf function is equivalent to wscanf, with the variable argument list
replaced by arg, which shall have been initialized by the va_start macro (andpossibly subsequent va_arg calls). The vwscanf function does not invoke theva_end macro.291)
Returns3

The vwscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the vwscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

7.24.2.11 The wprintf function
Synopsis1#include <wchar.h>
int wprintf(const wchar_t * restrict format, ...);
Description

2

The wprintf function is equivalent to fwprintf with the argument stdout
interposed before the arguments to wprintf.
Returns

3

The wprintf function returns the number of wide characters transmitted, or a negativevalue if an output or encoding error occurred.

7.24.2.12 The wscanf function
Synopsis1#include <wchar.h>
int wscanf(const wchar_t * restrict format, ...);
Description

2

The wscanf function is equivalent to fwscanf with the argument stdin interposed
before the arguments to wscanf.

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Returns
3

The wscanf function returns the value of the macro EOF if an input failure occurs
before any conversion. Otherwise, the wscanf function returns the number of input
items assigned, which can be fewer than provided for, or even zero, in the event of anearly matching failure.

7.24.3 Wide character input/output functions
7.24.3.1 The fgetwc function
Synopsis1#include <stdio.h>#include <wchar.h>
wint_t fgetwc(FILE *stream);
Description

2

If the end-of-file indicator for the input stream pointed to by stream is not set and anext wide character is present, the fgetwc function obtains that wide character as awchar_t converted to a wint_t and advances the associated file position indicator forthe stream (if defined).
Returns3

If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the endof-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
the fgetwc function returns the next wide character from the input stream pointed to bystream. If a read error occurs, the error indicator for the stream is set and the fgetwc
function returns WEOF. If an encoding error occurs (including too few bytes), the value ofthe macro EILSEQ is stored in errno and the fgetwc function returns WEOF.292)

7.24.3.2 The fgetws function
Synopsis1#include <stdio.h>#include <wchar.h>wchar_t *fgetws(wchar_t * restrict s,
int n, FILE * restrict stream);
Description

2

The fgetws function reads at most one less than the number of wide characters
specified by n from the stream pointed to by stream into the array pointed to by s. No292) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.

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additional wide characters are read after a new-line wide character (which is retained) orafter end-of-file. A null wide character is written immediately after the last wide
character read into the array.
Returns
3

The fgetws function returns s if successful. If end-of-file is encountered and no
characters have been read into the array, the contents of the array remain unchanged and anull pointer is returned. If a read or encoding error occurs during the operation, the array
contents are indeterminate and a null pointer is returned.

7.24.3.3 The fputwc function
Synopsis1#include <stdio.h>#include <wchar.h>
wint_t fputwc(wchar_t c, FILE *stream);
Description

2

The fputwc function writes the wide character specified by c to the output stream
pointed to by stream, at the position indicated by the associated file position indicator
for the stream (if defined), and advances the indicator appropriately. If the file cannot
support positioning requests, or if the stream was opened with append mode, thecharacter is appended to the output stream.
Returns

3

The fputwc function returns the wide character written. If a write error occurs, theerror indicator for the stream is set and fputwc returns WEOF. If an encoding error
occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.

7.24.3.4 The fputws function
Synopsis1#include <stdio.h>#include <wchar.h>
int fputws(const wchar_t * restrict s,
FILE * restrict stream);
Description

2

The fputws function writes the wide string pointed to by s to the stream pointed to bystream. The terminating null wide character is not written.
Returns

3

The fputws function returns EOF if a write or encoding error occurs; otherwise, it
returns a nonnegative value.
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7.24.3.5 The fwide function
Synopsis1#include <stdio.h>#include <wchar.h>
int fwide(FILE *stream, int mode);
Description

2

The fwide function determines the orientation of the stream pointed to by stream. If
mode is greater than zero, the function first attempts to make the stream wide oriented. Ifmode is less than zero, the function first attempts to make the stream byte oriented.293)
Otherwise, mode is zero and the function does not alter the orientation of the stream.
Returns

3

The fwide function returns a value greater than zero if, after the call, the stream has
wide orientation, a value less than zero if the stream has byte orientation, or zero if thestream has no orientation.

7.24.3.6 The getwc function
Synopsis1#include <stdio.h>#include <wchar.h>
wint_t getwc(FILE *stream);
Description

2

The getwc function is equivalent to fgetwc, except that if it is implemented as a
macro, it may evaluate stream more than once, so the argument should never be an
expression with side effects.
Returns

3

The getwc function returns the next wide character from the input stream pointed to bystream, or WEOF.

7.24.3.7 The getwchar function
Synopsis1#include <wchar.h>
wint_t getwchar(void);293) If the orientation of the stream has already been determined, fwide does not change it.

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Description
2

The getwchar function is equivalent to getwc with the argument stdin.
Returns

3

The getwchar function returns the next wide character from the input stream pointed toby stdin, or WEOF.

7.24.3.8 The putwc function
Synopsis1#include <stdio.h>#include <wchar.h>
wint_t putwc(wchar_t c, FILE *stream);
Description

2

The putwc function is equivalent to fputwc, except that if it is implemented as a
macro, it may evaluate stream more than once, so that argument should never be an
expression with side effects.
Returns3

The putwc function returns the wide character written, or WEOF.

7.24.3.9 The putwchar function
Synopsis1#include <wchar.h>
wint_t putwchar(wchar_t c);
Description

2

The putwchar function is equivalent to putwc with the second argument stdout.
Returns3

The putwchar function returns the character written, or WEOF.

7.24.3.10 The ungetwc function
Synopsis1#include <stdio.h>#include <wchar.h>
wint_t ungetwc(wint_t c, FILE *stream);
Description

2

The ungetwc function pushes the wide character specified by c back onto the input
stream pointed to by stream. Pushed-back wide characters will be returned bysubsequent reads on that stream in the reverse order of their pushing. A successful
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intervening call (with the stream pointed to by stream) to a file positioning function(fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
stream. The external storage corresponding to the stream is unchanged.
3

One wide character of pushback is guaranteed, even if the call to the ungetwc function
follows just after a call to a formatted wide character input function fwscanf,
vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
on the same stream without an intervening read or file positioning operation on thatstream, the operation may fail.

4

If the value of c equals that of the macro WEOF, the operation fails and the input stream isunchanged.

5

A successful call to the ungetwc function clears the end-of-file indicator for the stream.
The value of the file position indicator for the stream after reading or discarding all
pushed-back wide characters is the same as it was before the wide characters were pushed
back. For a text or binary stream, the value of its file position indicator after a successful
call to the ungetwc function is unspecified until all pushed-back wide characters areread or discarded.
Returns

6

The ungetwc function returns the wide character pushed back, or WEOF if the operation
fails.

7.24.4 General wide string utilities
1

The header <wchar.h> declares a number of functions useful for wide string
manipulation. Various methods are used for determining the lengths of the arrays, but inall cases a wchar_t * argument points to the initial (lowest addressed) element of thearray. If an array is accessed beyond the end of an object, the behavior is undefined.

2

Where an argument declared as size_t n determines the length of the array for afunction, n can have the value zero on a call to that function. Unless explicitly statedotherwise in the description of a particular function in this subclause, pointer arguments
on such a call shall still have valid values, as described in 7.1.4. On such a call, afunction that locates a wide character finds no occurrence, a function that compares twowide character sequences returns zero, and a function that copies wide characters copies
zero wide characters.

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7.24.4.1 Wide string numeric conversion functions
7.24.4.1.1 The wcstod, wcstof, and wcstold functions
Synopsis1#include <wchar.h>double wcstod(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
float wcstof(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
long double wcstold(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
Description

2

The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
string pointed to by nptr to double, float, and long double representation,
respectively. First, they decompose the input string into three parts: an initial, possibly
empty, sequence of white-space wide characters (as specified by the iswspacefunction), a subject sequence resembling a floating-point constant or representing an
infinity or NaN; and a final wide string of one or more unrecognized wide characters,
including the terminating null wide character of the input wide string. Then, they attempt
to convert the subject sequence to a floating-point number, and return the result.

3

The expected form of the subject sequence is an optional plus or minus sign, then one of
the following:— a nonempty sequence of decimal digits optionally containing a decimal-point wide
character, then an optional exponent part as defined for the corresponding single-bytecharacters in 6.4.4.2;— a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing adecimal-point wide character, then an optional binary exponent part as defined in
6.4.4.2;— INF or INFINITY, or any other wide string equivalent except for case

— NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except forcase in the NAN part, where:n-wchar-sequence:
digit
nondigitn-wchar-sequence digit
n-wchar-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input wide
string, starting with the first non-white-space wide character, that is of the expected form.
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The subject sequence contains no wide characters if the input wide string is not of the
expected form.
4

If the subject sequence has the expected form for a floating-point number, the sequence ofwide characters starting with the first digit or the decimal-point wide character(whichever occurs first) is interpreted as a floating constant according to the rules of
6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
if neither an exponent part nor a decimal-point wide character appears in a decimal
floating point number, or if a binary exponent part does not appear in a hexadecimal
floating point number, an exponent part of the appropriate type with value zero isassumed to follow the last digit in the string. If the subject sequence begins with a minus
sign, the sequence is interpreted as negated.294) A wide character sequence INF or
INFINITY is interpreted as an infinity, if representable in the return type, else like afloating constant that is too large for the range of the return type. A wide character
sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
in the return type, else like a subject sequence part that does not have the expected form;
the meaning of the n-wchar sequences is implementation-defined.295) A pointer to thefinal wide string is stored in the object pointed to by endptr, provided that endptr is
not a null pointer.

5

If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, thevalue resulting from the conversion is correctly rounded.

6

In other than the "C" locale, additional locale-specific subject sequence forms may be
accepted.

7

If the subject sequence is empty or does not have the expected form, no conversion is
performed; the value of nptr is stored in the object pointed to by endptr, provided
that endptr is not a null pointer.
Recommended practice8

If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, andthe result is not exactly representable, the result should be one of the two numbers in theappropriate internal format that are adjacent to the hexadecimal floating source value,with the extra stipulation that the error should have a correct sign for the current rounding
direction.

294) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
methods may yield different results if rounding is toward positive or negative infinity. In either case,the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
295) An implementation may use the n-wchar sequence to determine extra information to be represented in
the NaN’s significand.

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If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in<float.h>) significant digits, the result should be correctly rounded. If the subject
sequence D has the decimal form and more than DECIMAL_DIG significant digits,
consider the two bounding, adjacent decimal strings L and U, both having
DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L ≤ D ≤ U.
The result should be one of the (equal or adjacent) values that would be obtained bycorrectly rounding L and U according to the current rounding direction, with the extra
stipulation that the error with respect to D should have a correct sign for the current
rounding direction.296)
Returns

10

The functions return the converted value, if any. If no conversion could be performed,
zero is returned. If the correct value is outside the range of representable values, plus orminus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return
type and sign of the value), and the value of the macro ERANGE is stored in errno. If
the result underflows (7.12.1), the functions return a value whose magnitude is no greaterthan the smallest normalized positive number in the return type; whether errno acquires
the value ERANGE is implementation-defined.

296) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually roundto the same internal floating value, but if not will round to adjacent values.

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7.24.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
Synopsis1#include <wchar.h>long int wcstol(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);long long int wcstoll(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
unsigned long int wcstoul(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
unsigned long long int wcstoull(const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
Description

2

The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
portion of the wide string pointed to by nptr to long int, long long int,
unsigned long int, and unsigned long long int representation,
respectively. First, they decompose the input string into three parts: an initial, possibly
empty, sequence of white-space wide characters (as specified by the iswspacefunction), a subject sequence resembling an integer represented in some radix determinedby the value of base, and a final wide string of one or more unrecognized wide
characters, including the terminating null wide character of the input wide string. Then,they attempt to convert the subject sequence to an integer, and return the result.

3

If the value of base is zero, the expected form of the subject sequence is that of an
integer constant as described for the corresponding single-byte characters in 6.4.4.1,
optionally preceded by a plus or minus sign, but not including an integer suffix. If thevalue of base is between 2 and 36 (inclusive), the expected form of the subject sequenceis a sequence of letters and digits representing an integer with the radix specified bybase, optionally preceded by a plus or minus sign, but not including an integer suffix.
The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
letters and digits whose ascribed values are less than that of base are permitted. If thevalue of base is 16, the wide characters 0x or 0X may optionally precede the sequenceof letters and digits, following the sign if present.
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4

The subject sequence is defined as the longest initial subsequence of the input wide
string, starting with the first non-white-space wide character, that is of the expected form.
The subject sequence contains no wide characters if the input wide string is empty or
consists entirely of white space, or if the first non-white-space wide character is otherthan a sign or a permissible letter or digit.

5

If the subject sequence has the expected form and the value of base is zero, the sequenceof wide characters starting with the first digit is interpreted as an integer constantaccording to the rules of 6.4.4.1. If the subject sequence has the expected form and thevalue of base is between 2 and 36, it is used as the base for conversion, ascribing to eachletter its value as given above. If the subject sequence begins with a minus sign, the value
resulting from the conversion is negated (in the return type). A pointer to the final wide
string is stored in the object pointed to by endptr, provided that endptr is not a nullpointer.

6

In other than the "C" locale, additional locale-specific subject sequence forms may be
accepted.

7

If the subject sequence is empty or does not have the expected form, no conversion is
performed; the value of nptr is stored in the object pointed to by endptr, provided
that endptr is not a null pointer.
Returns

8

The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
value, if any. If no conversion could be performed, zero is returned. If the correct value
is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return typesign of the value, if any), and the value of the macro ERANGE is stored in errno.

7.24.4.2 Wide string copying functions
7.24.4.2.1 The wcscpy function
Synopsis1#include <wchar.h>wchar_t *wcscpy(wchar_t * restrict s1,
const wchar_t * restrict s2);
Description

2

The wcscpy function copies the wide string pointed to by s2 (including the terminatingnull wide character) into the array pointed to by s1.
Returns

3

The wcscpy function returns the value of s1.

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7.24.4.2.2 The wcsncpy function
Synopsis1#include <wchar.h>wchar_t *wcsncpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description

2

The wcsncpy function copies not more than n wide characters (those that follow a nullwide character are not copied) from the array pointed to by s2 to the array pointed to bys1.297)3

If the array pointed to by s2 is a wide string that is shorter than n wide characters, nullwide characters are appended to the copy in the array pointed to by s1, until n wide
characters in all have been written.
Returns

4

The wcsncpy function returns the value of s1.

7.24.4.2.3 The wmemcpy function
Synopsis1#include <wchar.h>wchar_t *wmemcpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description

2

The wmemcpy function copies n wide characters from the object pointed to by s2 to theobject pointed to by s1.
Returns

3

The wmemcpy function returns the value of s1.

297) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, theresult will not be null-terminated.

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7.24.4.2.4 The wmemmove function
Synopsis1#include <wchar.h>wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
size_t n);
Description

2

The wmemmove function copies n wide characters from the object pointed to by s2 tothe object pointed to by s1. Copying takes place as if the n wide characters from theobject pointed to by s2 are first copied into a temporary array of n wide characters that
does not overlap the objects pointed to by s1 or s2, and then the n wide characters fromthe temporary array are copied into the object pointed to by s1.
Returns

3

The wmemmove function returns the value of s1.

7.24.4.3 Wide string concatenation functions
7.24.4.3.1 The wcscat function
Synopsis1#include <wchar.h>wchar_t *wcscat(wchar_t * restrict s1,
const wchar_t * restrict s2);
Description

2

The wcscat function appends a copy of the wide string pointed to by s2 (including theterminating null wide character) to the end of the wide string pointed to by s1. The initialwide character of s2 overwrites the null wide character at the end of s1.
Returns

3

The wcscat function returns the value of s1.

7.24.4.3.2 The wcsncat function
Synopsis1#include <wchar.h>wchar_t *wcsncat(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description

2

The wcsncat function appends not more than n wide characters (a null wide characterand those that follow it are not appended) from the array pointed to by s2 to the end of378

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the wide string pointed to by s1. The initial wide character of s2 overwrites the nullwide character at the end of s1. A terminating null wide character is always appended to
the result.298)
Returns
3

The wcsncat function returns the value of s1.

7.24.4.4 Wide string comparison functions
1

Unless explicitly stated otherwise, the functions described in this subclause order two
wide characters the same way as two integers of the underlying integer type designatedby wchar_t.

7.24.4.4.1 The wcscmp function
Synopsis1#include <wchar.h>
int wcscmp(const wchar_t *s1, const wchar_t *s2);
Description

2

The wcscmp function compares the wide string pointed to by s1 to the wide string
pointed to by s2.
Returns

3

The wcscmp function returns an integer greater than, equal to, or less than zero,accordingly as the wide string pointed to by s1 is greater than, equal to, or less than thewide string pointed to by s2.

7.24.4.4.2 The wcscoll function
Synopsis1#include <wchar.h>
int wcscoll(const wchar_t *s1, const wchar_t *s2);
Description

2

The wcscoll function compares the wide string pointed to by s1 to the wide string
pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of thecurrent locale.
Returns

3

The wcscoll function returns an integer greater than, equal to, or less than zero,accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the298) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
wcslen(s1)+n+1.

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wide string pointed to by s2 when both are interpreted as appropriate to the current
locale.

7.24.4.4.3 The wcsncmp function
Synopsis1#include <wchar.h>
int wcsncmp(const wchar_t *s1, const wchar_t *s2,
size_t n);
Description

2

The wcsncmp function compares not more than n wide characters (those that follow anull wide character are not compared) from the array pointed to by s1 to the arraypointed to by s2.
Returns

3

The wcsncmp function returns an integer greater than, equal to, or less than zero,accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
to, or less than the possibly null-terminated array pointed to by s2.

7.24.4.4.4 The wcsxfrm function
Synopsis1#include <wchar.h>size_t wcsxfrm(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description

2

The wcsxfrm function transforms the wide string pointed to by s2 and places theresulting wide string into the array pointed to by s1. The transformation is such that if
the wcscmp function is applied to two transformed wide strings, it returns a value greater
than, equal to, or less than zero, corresponding to the result of the wcscoll function
applied to the same two original wide strings. No more than n wide characters are placed
into the resulting array pointed to by s1, including the terminating null wide character. If
n is zero, s1 is permitted to be a null pointer.
Returns

3

The wcsxfrm function returns the length of the transformed wide string (not including
the terminating null wide character). If the value returned is n or greater, the contents of
the array pointed to by s1 are indeterminate.

4

EXAMPLE The value of the following expression is the length of the array needed to hold thetransformation of the wide string pointed to by s:

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1 + wcsxfrm(NULL, s, 0)7.24.4.4.5 The wmemcmp function
Synopsis1#include <wchar.h>
int wmemcmp(const wchar_t *s1, const wchar_t *s2,
size_t n);
Description

2

The wmemcmp function compares the first n wide characters of the object pointed to by
s1 to the first n wide characters of the object pointed to by s2.
Returns

3

The wmemcmp function returns an integer greater than, equal to, or less than zero,accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
pointed to by s2.

7.24.4.5 Wide string search functions
7.24.4.5.1 The wcschr function
Synopsis1#include <wchar.h>wchar_t *wcschr(const wchar_t *s, wchar_t c);
Description

2

The wcschr function locates the first occurrence of c in the wide string pointed to by s.
The terminating null wide character is considered to be part of the wide string.
Returns

3

The wcschr function returns a pointer to the located wide character, or a null pointer if
the wide character does not occur in the wide string.

7.24.4.5.2 The wcscspn function
Synopsis1#include <wchar.h>size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
Description

2

The wcscspn function computes the length of the maximum initial segment of the wide
string pointed to by s1 which consists entirely of wide characters not from the wide
string pointed to by s2.

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Returns
3

The wcscspn function returns the length of the segment.

7.24.4.5.3 The wcspbrk function
Synopsis1#include <wchar.h>wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
Description

2

The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
any wide character from the wide string pointed to by s2.
Returns

3

The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
no wide character from s2 occurs in s1.

7.24.4.5.4 The wcsrchr function
Synopsis1#include <wchar.h>wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
Description

2

The wcsrchr function locates the last occurrence of c in the wide string pointed to bys. The terminating null wide character is considered to be part of the wide string.
Returns

3

The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
not occur in the wide string.

7.24.4.5.5 The wcsspn function
Synopsis1#include <wchar.h>size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
Description

2

The wcsspn function computes the length of the maximum initial segment of the wide
string pointed to by s1 which consists entirely of wide characters from the wide string
pointed to by s2.
Returns

3

The wcsspn function returns the length of the segment.
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7.24.4.5.6 The wcsstr function
Synopsis1#include <wchar.h>wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
Description

2

The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
the sequence of wide characters (excluding the terminating null wide character) in thewide string pointed to by s2.
Returns

3

The wcsstr function returns a pointer to the located wide string, or a null pointer if thewide string is not found. If s2 points to a wide string with zero length, the function
returns s1.

7.24.4.5.7 The wcstok function
Synopsis1#include <wchar.h>wchar_t *wcstok(wchar_t * restrict s1,
const wchar_t * restrict s2,
wchar_t ** restrict ptr);
Description

2

A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
a sequence of tokens, each of which is delimited by a wide character from the wide string
pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
which the wcstok function stores information necessary for it to continue scanning thesame wide string.

3

The first call in a sequence has a non-null first argument and stores an initial value in theobject pointed to by ptr. Subsequent calls in the sequence have a null first argument andthe object pointed to by ptr is required to have the value stored by the previous call inthe sequence, which is then updated. The separator wide string pointed to by s2 may bedifferent from call to call.

4

The first call in the sequence searches the wide string pointed to by s1 for the first wide
character that is not contained in the current separator wide string pointed to by s2. If nosuch wide character is found, then there are no tokens in the wide string pointed to by s1
and the wcstok function returns a null pointer. If such a wide character is found, it is
the start of the first token.

5

The wcstok function then searches from there for a wide character that is contained in
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extends to the end of the wide string pointed to by s1, and subsequent searches in thesame wide string for a token return a null pointer. If such a wide character is found, it isoverwritten by a null wide character, which terminates the current token.
6

In all cases, the wcstok function stores sufficient information in the pointer pointed toby ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointervalue for ptr, shall start searching just past the element overwritten by a null wide
character (if any).
Returns

7

The wcstok function returns a pointer to the first wide character of a token, or a nullpointer if there is no token.

8

EXAMPLE#include <wchar.h>static wchar_t str1[] = L"?a???b,,,#c";static wchar_t str2[] = L"\t \t";wchar_t *t, *ptr1, *ptr2;
t = wcstok(str1, L"?", &ptr1);
t = wcstok(NULL, L",", &ptr1);
t = wcstok(str2, L" \t", &ptr2);
t = wcstok(NULL, L"#,", &ptr1);
t = wcstok(NULL, L"?", &ptr1);// t points to the token L"a"// t points to the token L"??b"// t is a null pointer// t points to the token L"c"// t is a null pointer7.24.4.5.8 The wmemchr function
Synopsis1#include <wchar.h>wchar_t *wmemchr(const wchar_t *s, wchar_t c,size_t n);
Description

2

The wmemchr function locates the first occurrence of c in the initial n wide characters of
the object pointed to by s.
Returns

3

The wmemchr function returns a pointer to the located wide character, or a null pointer if
the wide character does not occur in the object.

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7.24.4.6 Miscellaneous functions
7.24.4.6.1 The wcslen function
Synopsis1#include <wchar.h>size_t wcslen(const wchar_t *s);
Description

2

The wcslen function computes the length of the wide string pointed to by s.
Returns

3

The wcslen function returns the number of wide characters that precede the terminatingnull wide character.

7.24.4.6.2 The wmemset function
Synopsis1#include <wchar.h>wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
Description

2

The wmemset function copies the value of c into each of the first n wide characters of
the object pointed to by s.
Returns

3

The wmemset function returns the value of s.

7.24.5 Wide character time conversion functions
7.24.5.1 The wcsftime function
Synopsis1#include <time.h>#include <wchar.h>size_t wcsftime(wchar_t * restrict s,size_t maxsize,
const wchar_t * restrict format,
const struct tm * restrict timeptr);
Description

2

The wcsftime function is equivalent to the strftime function, except that:— The argument s points to the initial element of an array of wide characters into which
the generated output is to be placed.

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— The argument format is a wide string and the conversion specifiers are replaced bycorresponding sequences of wide characters.
— The return value indicates the number of wide characters.
Returns3

If the total number of resulting wide characters including the terminating null wide
character is not more than maxsize, the wcsftime function returns the number ofwide characters placed into the array pointed to by s not including the terminating nullwide character. Otherwise, zero is returned and the contents of the array areindeterminate.

7.24.6 Extended multibyte/wide character conversion utilities
1

The header <wchar.h> declares an extended set of functions useful for conversion
between multibyte characters and wide characters.

2

Most of the following functions — those that are listed as ‘‘restartable’’, 7.24.6.3 and7.24.6.4 — take as a last argument a pointer to an object of type mbstate_t that is used
to describe the current conversion state from a particular multibyte character sequence toa wide character sequence (or the reverse) under the rules of a particular setting for the
LC_CTYPE category of the current locale.

3

The initial conversion state corresponds, for a conversion in either direction, to thebeginning of a new multibyte character in the initial shift state. A zero-valued
mbstate_t object is (at least) one way to describe an initial conversion state. A zerovalued mbstate_t object can be used to initiate conversion involving any multibyte
character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
been altered by any of the functions described in this subclause, and is then used with adifferent multibyte character sequence, or in the other conversion direction, or with adifferent LC_CTYPE category setting than on earlier function calls, the behavior isundefined.299)

4

On entry, each function takes the described conversion state (either internal or pointed toby an argument) as current. The conversion state described by the pointed-to object isaltered as needed to track the shift state, and the position within a multibyte character, forthe associated multibyte character sequence.

299) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc andmbsrtowcs functions as long as they are used to step sequentially through the same multibyte
character string.

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7.24.6.1 Single-byte/wide character conversion functions
7.24.6.1.1 The btowc function
Synopsis1#include <stdio.h>#include <wchar.h>
wint_t btowc(int c);
Description

2

The btowc function determines whether c constitutes a valid single-byte character in theinitial shift state.
Returns3

The btowc function returns WEOF if c has the value EOF or if (unsigned char)cdoes not constitute a valid single-byte character in the initial shift state. Otherwise, it
returns the wide character representation of that character.

7.24.6.1.2 The wctob function
Synopsis1#include <stdio.h>#include <wchar.h>
int wctob(wint_t c);
Description

2

The wctob function determines whether c corresponds to a member of the extended
character set whose multibyte character representation is a single byte when in the initial
shift state.
Returns

3

The wctob function returns EOF if c does not correspond to a multibyte character withlength one in the initial shift state. Otherwise, it returns the single-byte representation ofthat character as an unsigned char converted to an int.

7.24.6.2 Conversion state functions
7.24.6.2.1 The mbsinit function
Synopsis1#include <wchar.h>
int mbsinit(const mbstate_t *ps);
Description2

If ps is not a null pointer, the mbsinit function determines whether the pointed-to
mbstate_t object describes an initial conversion state.
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Returns3

The mbsinit function returns nonzero if ps is a null pointer or if the pointed-to object
describes an initial conversion state; otherwise, it returns zero.

7.24.6.3 Restartable multibyte/wide character conversion functions
1

These functions differ from the corresponding multibyte character functions of 7.20.7(mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of typepointer to mbstate_t that points to an object that can completely describe the current
conversion state of the associated multibyte character sequence. If ps is a null pointer,each function uses its own internal mbstate_t object instead, which is initialized at
program startup to the initial conversion state. The implementation behaves as if nolibrary function calls these functions with a null pointer for ps.

2

Also unlike their corresponding functions, the return value does not represent whether theencoding is state-dependent.

7.24.6.3.1 The mbrlen function
Synopsis1#include <wchar.h>size_t mbrlen(const char * restrict s,size_t n,
mbstate_t * restrict ps);
Description

2

The mbrlen function is equivalent to the call:mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
where internal is the mbstate_t object for the mbrlen function, except that theexpression designated by ps is evaluated only once.
Returns3

The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
or (size_t)(-1).
Forward references: the mbrtowc function (7.24.6.3.2).

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7.24.6.3.2 The mbrtowc function
Synopsis1#include <wchar.h>size_t mbrtowc(wchar_t * restrict pwc,
const char * restrict s,size_t n,
mbstate_t * restrict ps);
Description2

If s is a null pointer, the mbrtowc function is equivalent to the call:mbrtowc(NULL, "", 1, ps)
In this case, the values of the parameters pwc and n are ignored.

3

If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning withthe byte pointed to by s to determine the number of bytes needed to complete the next
multibyte character (including any shift sequences). If the function determines that thenext multibyte character is complete and valid, it determines the value of thecorresponding wide character and then, if pwc is not a null pointer, stores that value inthe object pointed to by pwc. If the corresponding wide character is the null wide
character, the resulting state described is the initial conversion state.
Returns

4

The mbrtowc function returns the first of the following that applies (given the current
conversion state):0

if the next n or fewer bytes complete the multibyte character that
corresponds to the null wide character (which is the value stored).

between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
character (which is the value stored); the value returned is the numberof bytes that complete the multibyte character.
(size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)multibyte character, and all n bytes have been processed (no value isstored).300)(size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
do not contribute to a complete and valid multibyte character (novalue is stored); the value of the macro EILSEQ is stored in errno,
and the conversion state is unspecified.
300) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at asequence of redundant shift sequences (for implementations with state-dependent encodings).

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7.24.6.3.3 The wcrtomb function
Synopsis1#include <wchar.h>size_t wcrtomb(char * restrict s,
wchar_t wc,
mbstate_t * restrict ps);
Description2

If s is a null pointer, the wcrtomb function is equivalent to the call
wcrtomb(buf, L'\0', ps)
where buf is an internal buffer.

3

If s is not a null pointer, the wcrtomb function determines the number of bytes needed
to represent the multibyte character that corresponds to the wide character given by wc(including any shift sequences), and stores the multibyte character representation in thearray whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
to restore the initial shift state; the resulting state described is the initial conversion state.
Returns

4

The wcrtomb function returns the number of bytes stored in the array object (including
any shift sequences). When wc is not a valid wide character, an encoding error occurs:
the function stores the value of the macro EILSEQ in errno and returns(size_t)(-1); the conversion state is unspecified.

7.24.6.4 Restartable multibyte/wide string conversion functions
1

These functions differ from the corresponding multibyte string functions of 7.20.8(mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer tombstate_t that points to an object that can completely describe the current conversion
state of the associated multibyte character sequence. If ps is a null pointer, each functionuses its own internal mbstate_t object instead, which is initialized at program startup
to the initial conversion state. The implementation behaves as if no library function calls
these functions with a null pointer for ps.

2

Also unlike their corresponding functions, the conversion source parameter, src, has apointer-to-pointer type. When the function is storing the results of conversions (that is,when dst is not a null pointer), the pointer object pointed to by this parameter is updated
to reflect the amount of the source processed by that invocation.

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7.24.6.4.1 The mbsrtowcs function
Synopsis1#include <wchar.h>size_t mbsrtowcs(wchar_t * restrict dst,
const char ** restrict src,
size_t len,mbstate_t * restrict ps);
Description

2

The mbsrtowcs function converts a sequence of multibyte characters that begins in theconversion state described by the object pointed to by ps, from the array indirectly
pointed to by src into a sequence of corresponding wide characters. If dst is not a nullpointer, the converted characters are stored into the array pointed to by dst. Conversion
continues up to and including a terminating null character, which is also stored.
Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
not form a valid multibyte character, or (if dst is not a null pointer) when len wide
characters have been stored into the array pointed to by dst.301) Each conversion takes
place as if by a call to the mbrtowc function.

3

If dst is not a null pointer, the pointer object pointed to by src is assigned either a nullpointer (if conversion stopped due to reaching a terminating null character) or the address
just past the last multibyte character converted (if any). If conversion stopped due toreaching a terminating null character and if dst is not a null pointer, the resulting state
described is the initial conversion state.
Returns

4

If the input conversion encounters a sequence of bytes that do not form a valid multibyte
character, an encoding error occurs: the mbsrtowcs function stores the value of themacro EILSEQ in errno and returns (size_t)(-1); the conversion state isunspecified. Otherwise, it returns the number of multibyte characters successfully
converted, not including the terminating null character (if any).

301) Thus, the value of len is ignored if dst is a null pointer.

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7.24.6.4.2 The wcsrtombs function
Synopsis1#include <wchar.h>size_t wcsrtombs(char * restrict dst,
const wchar_t ** restrict src,
size_t len,mbstate_t * restrict ps);
Description

2

The wcsrtombs function converts a sequence of wide characters from the array
indirectly pointed to by src into a sequence of corresponding multibyte characters thatbegins in the conversion state described by the object pointed to by ps. If dst is not anull pointer, the converted characters are then stored into the array pointed to by dst.
Conversion continues up to and including a terminating null wide character, which is also
stored. Conversion stops earlier in two cases: when a wide character is reached that does
not correspond to a valid multibyte character, or (if dst is not a null pointer) when thenext multibyte character would exceed the limit of len total bytes to be stored into thearray pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
function.302)

3

If dst is not a null pointer, the pointer object pointed to by src is assigned either a nullpointer (if conversion stopped due to reaching a terminating null wide character) or theaddress just past the last wide character converted (if any). If conversion stopped due toreaching a terminating null wide character, the resulting state described is the initialconversion state.
Returns4

If conversion stops because a wide character is reached that does not correspond to avalid multibyte character, an encoding error occurs: the wcsrtombs function stores thevalue of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
character sequence, not including the terminating null character (if any).

302) If conversion stops because a terminating null wide character has been reached, the bytes stored
include those necessary to reach the initial shift state immediately before the null byte.

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7.25 Wide character classification and mapping utilities <wctype.h>
7.25.1 Introduction
1

The header <wctype.h> declares three data types, one macro, and many functions.303)

2

The types declared are
wint_tdescribed in 7.24.1;
wctrans_t
which is a scalar type that can hold values which represent locale-specific charactermappings; andwctype_t
which is a scalar type that can hold values which represent locale-specific characterclassifications.

3

The macro defined is WEOF (described in 7.24.1).

4

The functions declared are grouped as follows:— Functions that provide wide character classification;— Extensible functions that provide wide character classification;— Functions that provide wide character case mapping;— Extensible functions that provide wide character mapping.

5

For all functions described in this subclause that accept an argument of type wint_t, thevalue shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
this argument has any other value, the behavior is undefined.

6

The behavior of these functions is affected by the LC_CTYPE category of the current
locale.

303) See ‘‘future library directions’’ (7.26.13).

§7.25.1

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7.25.2 Wide character classification utilities
1

The header <wctype.h> declares several functions useful for classifying wide
characters.

2

The term printing wide character refers to a member of a locale-specific set of wide
characters, each of which occupies at least one printing position on a display device. The
term control wide character refers to a member of a locale-specific set of wide charactersthat are not printing wide characters.

7.25.2.1 Wide character classification functions
1

The functions in this subclause return nonzero (true) if and only if the value of theargument wc conforms to that in the description of the function.

2

Each of the following functions returns true for each wide character that corresponds (asif by a call to the wctob function) to a single-byte character for which the corresponding
character classification function from 7.4.1 returns true, except that the iswgraph andiswpunct functions may differ with respect to wide characters other than L' ' that areboth printing and white-space wide characters.304)
Forward references: the wctob function (7.24.6.1.2).

7.25.2.1.1 The iswalnum function
Synopsis1#include <wctype.h>
int iswalnum(wint_t wc);
Description

2

The iswalnum function tests for any wide character for which iswalpha or
iswdigit is true.

7.25.2.1.2 The iswalpha function
Synopsis1#include <wctype.h>
int iswalpha(wint_t wc);
Description

2

The iswalpha function tests for any wide character for which iswupper or
iswlower is true, or any wide character that is one of a locale-specific set of alphabetic304) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
(which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)&& iswspace(wc) is true, but not both.

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wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspaceis true.305)

7.25.2.1.3 The iswblank function
Synopsis1#include <wctype.h>
int iswblank(wint_t wc);
Description

2

The iswblank function tests for any wide character that is a standard blank wide
character or is one of a locale-specific set of wide characters for which iswspace is true
and that is used to separate words within a line of text. The standard blank wide
characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
locale, iswblank returns true only for the standard blank characters.

7.25.2.1.4 The iswcntrl function
Synopsis1#include <wctype.h>
int iswcntrl(wint_t wc);
Description

2

The iswcntrl function tests for any control wide character.

7.25.2.1.5 The iswdigit function
Synopsis1#include <wctype.h>
int iswdigit(wint_t wc);
Description

2

The iswdigit function tests for any wide character that corresponds to a decimal-digit
character (as defined in 5.2.1).

7.25.2.1.6 The iswgraph function
Synopsis1#include <wctype.h>
int iswgraph(wint_t wc);305) The functions iswlower and iswupper test true or false separately for each of these additional
wide characters; all four combinations are possible.

§7.25.2.1.6

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Description
2

The iswgraph function tests for any wide character for which iswprint is true andiswspace is false.306)

7.25.2.1.7 The iswlower function
Synopsis1#include <wctype.h>
int iswlower(wint_t wc);
Description

2

The iswlower function tests for any wide character that corresponds to a lowercase
letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
iswdigit, iswpunct, or iswspace is true.

7.25.2.1.8 The iswprint function
Synopsis1#include <wctype.h>
int iswprint(wint_t wc);
Description

2

The iswprint function tests for any printing wide character.

7.25.2.1.9 The iswpunct function
Synopsis1#include <wctype.h>
int iswpunct(wint_t wc);
Description

2

The iswpunct function tests for any printing wide character that is one of a localespecific set of punctuation wide characters for which neither iswspace nor iswalnum
is true.306)

7.25.2.1.10 The iswspace function
Synopsis1#include <wctype.h>
int iswspace(wint_t wc);306) Note that the behavior of the iswgraph and iswpunct functions may differ from theircorresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
characters other than ' '.

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Description
2

The iswspace function tests for any wide character that corresponds to a locale-specific
set of white-space wide characters for which none of iswalnum, iswgraph, or
iswpunct is true.

7.25.2.1.11 The iswupper function
Synopsis1#include <wctype.h>
int iswupper(wint_t wc);
Description

2

The iswupper function tests for any wide character that corresponds to an uppercase
letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
iswdigit, iswpunct, or iswspace is true.

7.25.2.1.12 The iswxdigit function
Synopsis1#include <wctype.h>
int iswxdigit(wint_t wc);
Description

2

The iswxdigit function tests for any wide character that corresponds to ahexadecimal-digit character (as defined in 6.4.4.1).

7.25.2.2 Extensible wide character classification functions
1

The functions wctype and iswctype provide extensible wide character classification
as well as testing equivalent to that performed by the functions described in the previous
subclause (7.25.2.1).

7.25.2.2.1 The iswctype function
Synopsis1#include <wctype.h>
int iswctype(wint_t wc, wctype_t desc);
Description

2

The iswctype function determines whether the wide character wc has the property
described by desc. The current setting of the LC_CTYPE category shall be the same as
during the call to wctype that returned the value desc.

3

Each of the following expressions has a truth-value equivalent to the call to the wide
character classification function (7.25.2.1) in the comment that follows the expression:§7.25.2.2.1

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iswctype(wc, wctype("alnum"))
iswctype(wc, wctype("alpha"))iswctype(wc, wctype("blank"))
iswctype(wc, wctype("cntrl"))
iswctype(wc, wctype("digit"))iswctype(wc, wctype("graph"))iswctype(wc, wctype("lower"))
iswctype(wc, wctype("print"))
iswctype(wc, wctype("punct"))
iswctype(wc, wctype("space"))
iswctype(wc, wctype("upper"))
iswctype(wc, wctype("xdigit"))

WG14/N1256// iswalnum(wc)// iswalpha(wc)// iswblank(wc)// iswcntrl(wc)// iswdigit(wc)// iswgraph(wc)// iswlower(wc)// iswprint(wc)// iswpunct(wc)// iswspace(wc)// iswupper(wc)// iswxdigit(wc)Returns
4

The iswctype function returns nonzero (true) if and only if the value of the wide
character wc has the property described by desc.
Forward references: the wctype function (7.25.2.2.2).

7.25.2.2.2 The wctype function
Synopsis1#include <wctype.h>
wctype_t wctype(const char *property);
Description

2

The wctype function constructs a value with type wctype_t that describes a class ofwide characters identified by the string argument property.

3

The strings listed in the description of the iswctype function shall be valid in all
locales as property arguments to the wctype function.
Returns4

If property identifies a valid class of wide characters according to the LC_CTYPE
category of the current locale, the wctype function returns a nonzero value that is valid
as the second argument to the iswctype function; otherwise, it returns zero.
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7.25.3 Wide character case mapping utilities
1

The header <wctype.h> declares several functions useful for mapping wide characters.

7.25.3.1 Wide character case mapping functions
7.25.3.1.1 The towlower function
Synopsis1#include <wctype.h>
wint_t towlower(wint_t wc);
Description

2

The towlower function converts an uppercase letter to a corresponding lowercase letter.
Returns3

If the argument is a wide character for which iswupper is true and there are one ormore corresponding wide characters, as specified by the current locale, for which
iswlower is true, the towlower function returns one of the corresponding wide
characters (always the same one for any given locale); otherwise, the argument isreturned unchanged.

7.25.3.1.2 The towupper function
Synopsis1#include <wctype.h>
wint_t towupper(wint_t wc);
Description

2

The towupper function converts a lowercase letter to a corresponding uppercase letter.
Returns3

If the argument is a wide character for which iswlower is true and there are one ormore corresponding wide characters, as specified by the current locale, for which
iswupper is true, the towupper function returns one of the corresponding wide
characters (always the same one for any given locale); otherwise, the argument isreturned unchanged.

7.25.3.2 Extensible wide character case mapping functions
1

The functions wctrans and towctrans provide extensible wide character mapping aswell as case mapping equivalent to that performed by the functions described in theprevious subclause (7.25.3.1).

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7.25.3.2.1 The towctrans function
Synopsis1#include <wctype.h>
wint_t towctrans(wint_t wc, wctrans_t desc);
Description

2

The towctrans function maps the wide character wc using the mapping described bydesc. The current setting of the LC_CTYPE category shall be the same as during the callto wctrans that returned the value desc.

3

Each of the following expressions behaves the same as the call to the wide character casemapping function (7.25.3.1) in the comment that follows the expression:
towctrans(wc, wctrans("tolower"))
towctrans(wc, wctrans("toupper"))// towlower(wc)// towupper(wc)Returns
4

The towctrans function returns the mapped value of wc using the mapping describedby desc.

7.25.3.2.2 The wctrans function
Synopsis1#include <wctype.h>
wctrans_t wctrans(const char *property);
Description

2

The wctrans function constructs a value with type wctrans_t that describes a
mapping between wide characters identified by the string argument property.

3

The strings listed in the description of the towctrans function shall be valid in all
locales as property arguments to the wctrans function.
Returns4

If property identifies a valid mapping of wide characters according to the LC_CTYPE
category of the current locale, the wctrans function returns a nonzero value that is valid
as the second argument to the towctrans function; otherwise, it returns zero.

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7.26 Future library directions
1

The following names are grouped under individual headers for convenience. All external
names described below are reserved no matter what headers are included by the program.

7.26.1 Complex arithmetic <complex.h>1

The function names
cerf
cerfc
cexp2

cexpm1
clog10clog1pclog2
clgamma
ctgammaand the same names suffixed with f or l may be added to the declarations in the<complex.h> header.

7.26.2 Character handling <ctype.h>1Function names that begin with either is or to, and a lowercase letter may be added tothe declarations in the <ctype.h> header.

7.26.3 Errors <errno.h>1

Macros that begin with E and a digit or E and an uppercase letter may be added to thedeclarations in the <errno.h> header.

7.26.4 Format conversion of integer types <inttypes.h>1

Macro names beginning with PRI or SCN followed by any lowercase letter or X may be
added to the macros defined in the <inttypes.h> header.

7.26.5 Localization <locale.h>1

Macros that begin with LC_ and an uppercase letter may be added to the definitions in
the <locale.h> header.

7.26.6 Signal handling <signal.h>1Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
letter may be added to the definitions in the <signal.h> header.

7.26.7 Boolean type and values <stdbool.h>1

The ability to undefine and perhaps then redefine the macros bool, true, and false isan obsolescent feature.

7.26.8 Integer types <stdint.h>
1

Typedef names beginning with int or uint and ending with _t may be added to thetypes defined in the <stdint.h> header. Macro names beginning with INT or UINT
and ending with _MAX, _MIN, or _C may be added to the macros defined in the<stdint.h> header.
§7.26.8

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7.26.9 Input/output <stdio.h>1

Lowercase letters may be added to the conversion specifiers and length modifiers in
fprintf and fscanf. Other characters may be used in extensions.

2

The gets function is obsolescent, and is deprecated.

3

The use of ungetc on a binary stream where the file position indicator is zero prior tothe call is an obsolescent feature.

7.26.10 General utilities <stdlib.h>1Function names that begin with str and a lowercase letter may be added to thedeclarations in the <stdlib.h> header.

7.26.11 String handling <string.h>1Function names that begin with str, mem, or wcs and a lowercase letter may be added
to the declarations in the <string.h> header.

7.26.12 Extended multibyte and wide character utilities <wchar.h>1Function names that begin with wcs and a lowercase letter may be added to thedeclarations in the <wchar.h> header.

2

Lowercase letters may be added to the conversion specifiers and length modifiers in
fwprintf and fwscanf. Other characters may be used in extensions.

7.26.13 Wide character classification and mapping utilities<wctype.h>1Function names that begin with is or to and a lowercase letter may be added to thedeclarations in the <wctype.h> header.

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Annex A
(informative)
Language syntax summary
1

NOTE

The notation is described in 6.1.

A.1 Lexical grammar
A.1.1 Lexical elements(6.4) token:
keywordidentifier
constant
string-literalpunctuator(6.4) preprocessing-token:
header-nameidentifier
pp-numbercharacter-constantstring-literalpunctuator
each non-white-space character that cannot be one of the above

A.1.2 Keywords(6.4.1) keyword: one of
auto
break
case
char
const
continuedefaultdodoubleelse§A.1.2enum
extern
float
for
goto
if
inlineint
longregister

restrictreturnshort
signedsizeofstaticstructswitchtypedefunion

Language syntax summary

unsigned
void
volatile
while
_Bool
_Complex_Imaginary403ISO/IEC 9899:TC3

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A.1.3 Identifiers(6.4.2.1) identifier:identifier-nondigit
identifier identifier-nondigit
identifier digit(6.4.2.1) identifier-nondigit:
nondigit
universal-character-nameother implementation-defined characters(6.4.2.1) nondigit: one of_ a b c
n o p
A B C
N O P

d
q
D
Q

e
r
E
R

f
s
F
S

g
t
G
T

h
u
H
U

i
v
I
V

(6.4.2.1) digit: one of
0 1 2

4

5

6

7

8

9

3

j
w
J
W

k
x
K
X

l
y
L
Y

m
z
M
Z

A.1.4 Universal character names(6.4.3) universal-character-name:\u hex-quad\U hex-quad hex-quad(6.4.3) hex-quad:
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit

A.1.5 Constants(6.4.4) constant:
integer-constantfloating-constantenumeration-constantcharacter-constant(6.4.4.1) integer-constant:decimal-constant integer-suffixopt
octal-constant integer-suffixopt
hexadecimal-constant integer-suffixopt(6.4.4.1) decimal-constant:nonzero-digit
decimal-constant digit404

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ISO/IEC 9899:TC3(6.4.4.1) octal-constant:0octal-constant octal-digit(6.4.4.1) hexadecimal-constant:hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit(6.4.4.1) hexadecimal-prefix: one of
0x 0X(6.4.4.1) nonzero-digit: one of
1 2 3 4 567

8

(6.4.4.1) octal-digit: one of
0 1 2 3

5

6

7

6

7

4

(6.4.4.1) hexadecimal-digit: one of
0 1 2 3 4 5a b c d e f
A B C D E F

9

8

9

(6.4.4.1) integer-suffix:
unsigned-suffix long-suffixopt
unsigned-suffix long-long-suffix
long-suffix unsigned-suffixopt
long-long-suffix unsigned-suffixopt(6.4.4.1) unsigned-suffix: one ofu U(6.4.4.1) long-suffix: one ofl L(6.4.4.1) long-long-suffix: one ofll LL(6.4.4.2) floating-constant:decimal-floating-constanthexadecimal-floating-constant(6.4.4.2) decimal-floating-constant:fractional-constant exponent-partopt floating-suffixopt
digit-sequence exponent-part floating-suffixopt§A.1.5

Language syntax summary

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WG14/N1256(6.4.4.2) hexadecimal-floating-constant:hexadecimal-prefix hexadecimal-fractional-constantbinary-exponent-part floating-suffixopt
hexadecimal-prefix hexadecimal-digit-sequencebinary-exponent-part floating-suffixopt(6.4.4.2) fractional-constant:digit-sequenceopt . digit-sequence
digit-sequence .
(6.4.4.2) exponent-part:e signopt digit-sequence
E signopt digit-sequence(6.4.4.2) sign: one of+ (6.4.4.2) digit-sequence:
digit
digit-sequence digit(6.4.4.2) hexadecimal-fractional-constant:hexadecimal-digit-sequenceopt .
hexadecimal-digit-sequence
hexadecimal-digit-sequence .
(6.4.4.2) binary-exponent-part:p signopt digit-sequence
P signopt digit-sequence(6.4.4.2) hexadecimal-digit-sequence:
hexadecimal-digit
hexadecimal-digit-sequence hexadecimal-digit(6.4.4.2) floating-suffix: one off l F L(6.4.4.3) enumeration-constant:identifier(6.4.4.4) character-constant:' c-char-sequence 'L' c-char-sequence '406

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ISO/IEC 9899:TC3(6.4.4.4) c-char-sequence:c-charc-char-sequence c-char(6.4.4.4) c-char:
any member of the source character set except
the single-quote ', backslash \, or new-line character
escape-sequence(6.4.4.4) escape-sequence:
simple-escape-sequenceoctal-escape-sequence
hexadecimal-escape-sequence
universal-character-name(6.4.4.4) simple-escape-sequence: one of\' \" \? \\\a \b \f \n \r \t\v(6.4.4.4) octal-escape-sequence:\ octal-digit\ octal-digit octal-digit\ octal-digit octal-digit octal-digit(6.4.4.4) hexadecimal-escape-sequence:\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit

A.1.6 String literals(6.4.5) string-literal:" s-char-sequenceopt "L" s-char-sequenceopt "(6.4.5) s-char-sequence:s-chars-char-sequence s-char(6.4.5) s-char:
any member of the source character set except
the double-quote ", backslash \, or new-line character
escape-sequence§A.1.6

Language syntax summary

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A.1.7 Punctuators(6.4.6) punctuator: one of[ ] ( ) { } . ->++ -- & * + - ~ !
/ % << >> < > <= >=? : ; ...
= *= /= %= += -= <<=, # ##<: :> <% %> %: %:%:

==

!=

>>=

&=

^

|

&&

^=

|=

||

A.1.8 Header names(6.4.7) header-name:< h-char-sequence >" q-char-sequence "(6.4.7) h-char-sequence:h-charh-char-sequence h-char(6.4.7) h-char:
any member of the source character set except
the new-line character and >(6.4.7) q-char-sequence:q-charq-char-sequence q-char(6.4.7) q-char:
any member of the source character set except
the new-line character and "A.1.9 Preprocessing numbers(6.4.8) pp-number:digit. digitpp-number digit
pp-number identifier-nondigit
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
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A.2 Phrase structure grammar
A.2.1 Expressions(6.5.1) primary-expression:
identifier
constant
string-literal( expression )(6.5.2) postfix-expression:
primary-expression
postfix-expression [ expression ]postfix-expression ( argument-expression-listopt )postfix-expression . identifier
postfix-expression -> identifier
postfix-expression ++postfix-expression -( type-name ) { initializer-list }( type-name ) { initializer-list , }(6.5.2) argument-expression-list:
assignment-expression
argument-expression-list , assignment-expression(6.5.3) unary-expression:
postfix-expression++ unary-expression-- unary-expression
unary-operator cast-expression
sizeof unary-expression
sizeof ( type-name )(6.5.3) unary-operator: one of& * + - ~!

(6.5.4) cast-expression:
unary-expression( type-name ) cast-expression(6.5.5) multiplicative-expression:
cast-expression
multiplicative-expression * cast-expression
multiplicative-expression / cast-expression
multiplicative-expression % cast-expression§A.2.1

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WG14/N1256(6.5.6) additive-expression:
multiplicative-expression
additive-expression + multiplicative-expression
additive-expression - multiplicative-expression(6.5.7) shift-expression:
additive-expression
shift-expression << additive-expression
shift-expression >> additive-expression(6.5.8) relational-expression:
shift-expression
relational-expression < shift-expression
relational-expression > shift-expression
relational-expression <= shift-expression
relational-expression >= shift-expression(6.5.9) equality-expression:
relational-expression
equality-expression == relational-expression
equality-expression != relational-expression(6.5.10) AND-expression:equality-expression
AND-expression & equality-expression(6.5.11) exclusive-OR-expression:AND-expression
exclusive-OR-expression ^ AND-expression(6.5.12) inclusive-OR-expression:
exclusive-OR-expression
inclusive-OR-expression | exclusive-OR-expression(6.5.13) logical-AND-expression:
inclusive-OR-expression
logical-AND-expression && inclusive-OR-expression(6.5.14) logical-OR-expression:
logical-AND-expression
logical-OR-expression || logical-AND-expression(6.5.15) conditional-expression:
logical-OR-expression
logical-OR-expression ? expression : conditional-expression
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ISO/IEC 9899:TC3(6.5.16) assignment-expression:
conditional-expression
unary-expression assignment-operator assignment-expression(6.5.16) assignment-operator: one of= *= /= %= +=

-=

<<=

>>=

&=

^=

|=

(6.5.17) expression:
assignment-expression
expression , assignment-expression(6.6) constant-expression:
conditional-expression

A.2.2 Declarations(6.7) declaration:
declaration-specifiers init-declarator-listopt ;(6.7) declaration-specifiers:
storage-class-specifier declaration-specifiersopt
type-specifier declaration-specifiersopt
type-qualifier declaration-specifiersopt
function-specifier declaration-specifiersopt(6.7) init-declarator-list:
init-declarator
init-declarator-list , init-declarator(6.7) init-declarator:
declarator
declarator = initializer(6.7.1) storage-class-specifier:typedef
externstaticauto
register§A.2.2

Language syntax summary

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WG14/N1256(6.7.2) type-specifier:
void
char
short
int
long
float
doublesignedunsigned_Bool_Complex
struct-or-union-specifierenum-specifier
typedef-name∗(6.7.2.1) struct-or-union-specifier:struct-or-union identifieropt { struct-declaration-list }struct-or-union identifier(6.7.2.1) struct-or-union:
structunion(6.7.2.1) struct-declaration-list:
struct-declaration
struct-declaration-list struct-declaration(6.7.2.1) struct-declaration:
specifier-qualifier-list struct-declarator-list ;(6.7.2.1) specifier-qualifier-list:
type-specifier specifier-qualifier-listopt
type-qualifier specifier-qualifier-listopt(6.7.2.1) struct-declarator-list:
struct-declarator
struct-declarator-list , struct-declarator(6.7.2.1) struct-declarator:
declarator
declaratoropt : constant-expression

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ISO/IEC 9899:TC3(6.7.2.2) enum-specifier:enum identifieropt { enumerator-list }enum identifieropt { enumerator-list , }enum identifier(6.7.2.2) enumerator-list:
enumerator
enumerator-list , enumerator(6.7.2.2) enumerator:
enumeration-constantenumeration-constant = constant-expression(6.7.3) type-qualifier:
const
restrict
volatile(6.7.4) function-specifier:inline(6.7.5) declarator:
pointeropt direct-declarator(6.7.5) direct-declarator:
identifier( declarator )direct-declarator [ type-qualifier-listopt assignment-expressionopt ]direct-declarator [ static type-qualifier-listopt assignment-expression ]direct-declarator [ type-qualifier-list static assignment-expression ]direct-declarator [ type-qualifier-listopt * ]direct-declarator ( parameter-type-list )direct-declarator ( identifier-listopt )(6.7.5) pointer:* type-qualifier-listopt* type-qualifier-listopt pointer(6.7.5) type-qualifier-list:
type-qualifier
type-qualifier-list type-qualifier(6.7.5) parameter-type-list:
parameter-list
parameter-list , ...
§A.2.2

Language syntax summary

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WG14/N1256(6.7.5) parameter-list:
parameter-declaration
parameter-list , parameter-declaration(6.7.5) parameter-declaration:
declaration-specifiers declarator
declaration-specifiers abstract-declaratoropt(6.7.5) identifier-list:
identifier
identifier-list , identifier(6.7.6) type-name:specifier-qualifier-list abstract-declaratoropt(6.7.6) abstract-declarator:
pointerpointeropt direct-abstract-declarator(6.7.6) direct-abstract-declarator:( abstract-declarator )direct-abstract-declaratoropt [ type-qualifier-listopt
assignment-expressionopt ]direct-abstract-declaratoropt [ static type-qualifier-listopt
assignment-expression ]direct-abstract-declaratoropt [ type-qualifier-list static
assignment-expression ]direct-abstract-declaratoropt [ * ]direct-abstract-declaratoropt ( parameter-type-listopt )(6.7.7) typedef-name:identifier(6.7.8) initializer:
assignment-expression{ initializer-list }{ initializer-list , }(6.7.8) initializer-list:
designationopt initializer
initializer-list , designationopt initializer(6.7.8) designation:
designator-list =414

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ISO/IEC 9899:TC3(6.7.8) designator-list:
designator
designator-list designator(6.7.8) designator:[ constant-expression ]. identifier

A.2.3 Statements(6.8) statement:labeled-statement
compound-statement
expression-statement
selection-statement
iteration-statement
jump-statement(6.8.1) labeled-statement:
identifier : statementcase constant-expression : statement
default : statement(6.8.2) compound-statement:{ block-item-listopt }(6.8.2) block-item-list:
block-item
block-item-list block-item(6.8.2) block-item:
declaration
statement(6.8.3) expression-statement:
expressionopt ;(6.8.4) selection-statement:if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement§A.2.3

Language syntax summary

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WG14/N1256(6.8.5) iteration-statement:
while ( expression ) statement
do statement while ( expression ) ;for ( expressionopt ; expressionopt ; expressionopt ) statementfor ( declaration expressionopt ; expressionopt ) statement(6.8.6) jump-statement:
goto identifier ;continue ;break ;
return expressionopt ;A.2.4 External definitions(6.9) translation-unit:
external-declarationtranslation-unit external-declaration(6.9) external-declaration:function-definition
declaration(6.9.1) function-definition:
declaration-specifiers declarator declaration-listopt compound-statement(6.9.1) declaration-list:
declaration
declaration-list declaration

A.3 Preprocessing directives(6.10) preprocessing-file:groupopt(6.10) group:group-partgroup group-part(6.10) group-part:
if-section
control-line
text-line# non-directive(6.10) if-section:
if-group elif-groupsopt else-groupopt endif-line
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ISO/IEC 9899:TC3(6.10) if-group:# ifconstant-expression new-line groupopt# ifdef identifier new-line groupopt# ifndef identifier new-line groupopt(6.10) elif-groups:
elif-groupelif-groups elif-group(6.10) elif-group:# elifconstant-expression new-line groupopt(6.10) else-group:# elsenew-line groupopt(6.10) endif-line:# endif

new-line(6.10) control-line:# include pp-tokens new-line# define identifier replacement-list new-line# define identifier lparen identifier-listopt )replacement-list new-line# define identifier lparen ... ) replacement-list new-line# define identifier lparen identifier-list , ... )replacement-list new-line# undef
identifier new-line# linepp-tokens new-line# errorpp-tokensopt new-line# pragma pp-tokensopt new-line#
new-line(6.10) text-line:
pp-tokensopt new-line(6.10) non-directive:
pp-tokens new-line(6.10) lparen:a ( character not immediately preceded by white-space(6.10) replacement-list:
pp-tokensopt§A.3

Language syntax summary

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WG14/N1256(6.10) pp-tokens:
preprocessing-token
pp-tokens preprocessing-token(6.10) new-line:
the new-line character

418

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Annex B(informative)
Library summary
B.1 Diagnostics <assert.h>
NDEBUG
void assert(scalar expression);

B.2 Complex <complex.h>complex_Complex_I§B.2

imaginary_Imaginary_I

I#pragma STDC CX_LIMITED_RANGE on-off-switch
double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);
double complex casin(double complex z);
float complex casinf(float complex z);
long double complex casinl(long double complex z);
double complex catan(double complex z);
float complex catanf(float complex z);
long double complex catanl(long double complex z);
double complex ccos(double complex z);
float complex ccosf(float complex z);
long double complex ccosl(long double complex z);
double complex csin(double complex z);
float complex csinf(float complex z);
long double complex csinl(long double complex z);
double complex ctan(double complex z);
float complex ctanf(float complex z);
long double complex ctanl(long double complex z);
double complex cacosh(double complex z);
float complex cacoshf(float complex z);
long double complex cacoshl(long double complex z);
double complex casinh(double complex z);
float complex casinhf(float complex z);
long double complex casinhl(long double complex z);
double complex catanh(double complex z);
float complex catanhf(float complex z);
long double complex catanhl(long double complex z);
Library summary
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double complex ccosh(double complex z);
float complex ccoshf(float complex z);
long double complex ccoshl(long double complex z);
double complex csinh(double complex z);
float complex csinhf(float complex z);
long double complex csinhl(long double complex z);
double complex ctanh(double complex z);
float complex ctanhf(float complex z);
long double complex ctanhl(long double complex z);
double complex cexp(double complex z);
float complex cexpf(float complex z);
long double complex cexpl(long double complex z);
double complex clog(double complex z);
float complex clogf(float complex z);
long double complex clogl(long double complex z);
double cabs(double complex z);
float cabsf(float complex z);
long double cabsl(long double complex z);
double complex cpow(double complex x, double complex y);
float complex cpowf(float complex x, float complex y);long double complex cpowl(long double complex x,
long double complex y);
double complex csqrt(double complex z);
float complex csqrtf(float complex z);
long double complex csqrtl(long double complex z);
double carg(double complex z);
float cargf(float complex z);
long double cargl(long double complex z);
double cimag(double complex z);
float cimagf(float complex z);
long double cimagl(long double complex z);
double complex conj(double complex z);
float complex conjf(float complex z);
long double complex conjl(long double complex z);
double complex cproj(double complex z);
float complex cprojf(float complex z);
long double complex cprojl(long double complex z);
double creal(double complex z);
float crealf(float complex z);
long double creall(long double complex z);

420

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B.3 Character handling <ctype.h>
int isalnum(int c);
int isalpha(int c);
int isblank(int c);
int iscntrl(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);
int tolower(int c);
int toupper(int c);

B.4 Errors <errno.h>EDOM

EILSEQ

ERANGE

errno

B.5 Floating-point environment <fenv.h>
fenv_tfexcept_t
FE_DIVBYZERO
FE_INEXACT
FE_INVALID

FE_OVERFLOW
FE_UNDERFLOW
FE_ALL_EXCEPTFE_DOWNWARD
FE_TONEAREST

FE_TOWARDZERO
FE_UPWARD
FE_DFL_ENV#pragma STDC FENV_ACCESS on-off-switch
int feclearexcept(int excepts);
int fegetexceptflag(fexcept_t *flagp, int excepts);
int feraiseexcept(int excepts);
int fesetexceptflag(const fexcept_t *flagp,
int excepts);
int fetestexcept(int excepts);
int fegetround(void);
int fesetround(int round);int fegetenv(fenv_t *envp);
int feholdexcept(fenv_t *envp);
int fesetenv(const fenv_t *envp);
int feupdateenv(const fenv_t *envp);§B.5

Library summary

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B.6 Characteristics of floating types <float.h>
FLT_ROUNDSFLT_EVAL_METHOD
FLT_RADIX
FLT_MANT_DIG
DBL_MANT_DIG
LDBL_MANT_DIG
DECIMAL_DIG
FLT_DIG
DBL_DIG
LDBL_DIG
FLT_MIN_EXP

DBL_MIN_EXP
LDBL_MIN_EXP
FLT_MIN_10_EXP
DBL_MIN_10_EXP
LDBL_MIN_10_EXP
FLT_MAX_EXP
DBL_MAX_EXP
LDBL_MAX_EXP
FLT_MAX_10_EXP
DBL_MAX_10_EXP
LDBL_MAX_10_EXP

FLT_MAX
DBL_MAXLDBL_MAX
FLT_EPSILON
DBL_EPSILON
LDBL_EPSILON
FLT_MIN
DBL_MIN
LDBL_MIN

B.7 Format conversion of integer types <inttypes.h>
imaxdiv_t
PRIdN
PRIiN
PRIoN
PRIuN
PRIxN
PRIXN
SCNdN
SCNiN
SCNoN
SCNuN
SCNxN

PRIdLEASTNPRIiLEASTN
PRIoLEASTNPRIuLEASTNPRIxLEASTNPRIXLEASTNSCNdLEASTNSCNiLEASTN
SCNoLEASTNSCNuLEASTNSCNxLEASTN

PRIdFASTN
PRIiFASTN
PRIoFASTN
PRIuFASTN
PRIxFASTN
PRIXFASTN
SCNdFASTN
SCNiFASTN
SCNoFASTN
SCNuFASTN
SCNxFASTN

PRIdMAXPRIiMAXPRIoMAXPRIuMAXPRIxMAXPRIXMAXSCNdMAXSCNiMAXSCNoMAXSCNuMAXSCNxMAX

PRIdPTR
PRIiPTR
PRIoPTR
PRIuPTR
PRIxPTRPRIXPTR
SCNdPTR
SCNiPTR
SCNoPTRSCNuPTRSCNxPTRintmax_t imaxabs(intmax_t j);
imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);intmax_t strtoimax(const char * restrict nptr,
char ** restrict endptr, int base);uintmax_t strtoumax(const char * restrict nptr,
char ** restrict endptr, int base);
intmax_t wcstoimax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);uintmax_t wcstoumax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);

422

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B.8 Alternative spellings <iso646.h>andand_eqbitand

bitor
compl
not

not_eq
or
or_eq

xor
xor_eq

B.9 Sizes of integer types <limits.h>
CHAR_BITSCHAR_MIN
SCHAR_MAX
UCHAR_MAX
CHAR_MIN

CHAR_MAX
MB_LEN_MAX
SHRT_MINSHRT_MAX
USHRT_MAX

INT_MIN
INT_MAXUINT_MAXLONG_MIN
LONG_MAXULONG_MAXLLONG_MIN
LLONG_MAXULLONG_MAX

LC_CTYPE
LC_MONETARYLC_NUMERIC
LC_TIME

B.10 Localization <locale.h>struct lconv
NULL

LC_ALL
LC_COLLATE

char *setlocale(int category, const char *locale);struct lconv *localeconv(void);

B.11 Mathematics <math.h>float_tdouble_t
HUGE_VALHUGE_VALF
HUGE_VALL
INFINITYNAN

FP_INFINITE
FP_NANFP_NORMAL
FP_SUBNORMAL
FP_ZEROFP_FAST_FMA
FP_FAST_FMAF#pragma STDC FP_CONTRACT on-off-switch
int fpclassify(real-floating x);
int isfinite(real-floating x);
int isinf(real-floating x);
int isnan(real-floating x);
int isnormal(real-floating x);
int signbit(real-floating x);
double acos(double x);
float acosf(float x);
long double acosl(long double x);
double asin(double x);
float asinf(float x);
long double asinl(long double x);
double atan(double x);§B.11
Library summary

FP_FAST_FMAL
FP_ILOGB0
FP_ILOGBNAN
MATH_ERRNO
MATH_ERREXCEPT
math_errhandling423

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float atanf(float x);
long double atanl(long double x);
double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
double cos(double x);
float cosf(float x);
long double cosl(long double x);
double sin(double x);
float sinf(float x);
long double sinl(long double x);
double tan(double x);
float tanf(float x);
long double tanl(long double x);
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
double asinh(double x);
float asinhf(float x);
long double asinhl(long double x);
double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
double cosh(double x);
float coshf(float x);
long double coshl(long double x);
double sinh(double x);
float sinhf(float x);
long double sinhl(long double x);
double tanh(double x);
float tanhf(float x);
long double tanhl(long double x);
double exp(double x);
float expf(float x);
long double expl(long double x);
double exp2(double x);
float exp2f(float x);
long double exp2l(long double x);
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);424

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double frexp(double value, int *exp);
float frexpf(float value, int *exp);
long double frexpl(long double value, int *exp);
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long double x, int exp);
double log(double x);
float logf(float x);
long double logl(long double x);
double log10(double x);
float log10f(float x);
long double log10l(long double x);
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
double log2(double x);
float log2f(float x);
long double log2l(long double x);
double logb(double x);
float logbf(float x);
long double logbl(long double x);
double modf(double value, double *iptr);
float modff(float value, float *iptr);
long double modfl(long double value, long double *iptr);
double scalbn(double x, int n);
float scalbnf(float x, int n);long double scalbnl(long double x, int n);double scalbln(double x, long int n);
float scalblnf(float x, long int n);long double scalblnl(long double x, long int n);double cbrt(double x);
float cbrtf(float x);
long double cbrtl(long double x);
double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);
double hypot(double x, double y);float hypotf(float x, float y);§B.11

Library summary

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long double hypotl(long double x, long double y);
double pow(double x, double y);float powf(float x, float y);long double powl(long double x, long double y);
double sqrt(double x);
float sqrtf(float x);
long double sqrtl(long double x);
double erf(double x);
float erff(float x);
long double erfl(long double x);
double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);
double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);
double tgamma(double x);
float tgammaf(float x);
long double tgammal(long double x);
double ceil(double x);
float ceilf(float x);
long double ceill(long double x);
double floor(double x);
float floorf(float x);
long double floorl(long double x);
double nearbyint(double x);
float nearbyintf(float x);
long double nearbyintl(long double x);
double rint(double x);
float rintf(float x);
long double rintl(long double x);
long int lrint(double x);
long int lrintf(float x);
long int lrintl(long double x);
long long int llrint(double x);
long long int llrintf(float x);
long long int llrintl(long double x);
double round(double x);
float roundf(float x);
long double roundl(long double x);
long int lround(double x);
426

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long int lroundf(float x);
long int lroundl(long double x);
long long int llround(double x);
long long int llroundf(float x);
long long int llroundl(long double x);
double trunc(double x);
float truncf(float x);
long double truncl(long double x);
double fmod(double x, double y);float fmodf(float x, float y);long double fmodl(long double x, long double y);
double remainder(double x, double y);float remainderf(float x, float y);long double remainderl(long double x, long double y);
double remquo(double x, double y, int *quo);float remquof(float x, float y, int *quo);long double remquol(long double x, long double y,
int *quo);
double copysign(double x, double y);float copysignf(float x, float y);long double copysignl(long double x, long double y);
double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
double nextafter(double x, double y);float nextafterf(float x, float y);long double nextafterl(long double x, long double y);
double nexttoward(double x, long double y);float nexttowardf(float x, long double y);long double nexttowardl(long double x, long double y);
double fdim(double x, double y);float fdimf(float x, float y);long double fdiml(long double x, long double y);
double fmax(double x, double y);float fmaxf(float x, float y);long double fmaxl(long double x, long double y);
double fmin(double x, double y);float fminf(float x, float y);long double fminl(long double x, long double y);
double fma(double x, double y, double z);
float fmaf(float x, float y, float z);§B.11

Library summary

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long double fmal(long double x, long double y,long double z);
int isgreater(real-floating x, real-floating y);
int isgreaterequal(real-floating x, real-floating y);
int isless(real-floating x, real-floating y);
int islessequal(real-floating x, real-floating y);
int islessgreater(real-floating x, real-floating y);
int isunordered(real-floating x, real-floating y);

B.12 Nonlocal jumps <setjmp.h>
jmp_buf
int setjmp(jmp_buf env);
void longjmp(jmp_buf env, int val);

B.13 Signal handling <signal.h>sig_atomic_t
SIG_DFL
SIG_ERR

SIG_IGNSIGABRT
SIGFPE

SIGILLSIGINTSIGSEGVSIGTERM

void (*signal(int sig, void (*func)(int)))(int);
int raise(int sig);

B.14 Variable arguments <stdarg.h>
va_listtype va_arg(va_list ap, type);
void va_copy(va_list dest, va_list src);
void va_end(va_list ap);
void va_start(va_list ap, parmN);

B.15 Boolean type and values <stdbool.h>
bool
true
false
_ _bool_true_false_are_defined428

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B.16 Common definitions <stddef.h>
ptrdiff_t

size_twchar_t

NULL

offsetof(type, member-designator)

B.17 Integer types <stdint.h>
intN_tuintN_tint_leastN_t
uint_leastN_t
int_fastN_t
uint_fastN_t
intptr_t
uintptr_t
intmax_t
uintmax_t
INTN_MININTN_MAXUINTN_MAX

INT_LEASTN_MIN
INT_LEASTN_MAX
UINT_LEASTN_MAX
INT_FASTN_MIN
INT_FASTN_MAX
UINT_FASTN_MAX
INTPTR_MIN
INTPTR_MAXUINTPTR_MAX
INTMAX_MIN
INTMAX_MAXUINTMAX_MAXPTRDIFF_MIN

PTRDIFF_MAX
SIG_ATOMIC_MIN
SIG_ATOMIC_MAX
SIZE_MAXWCHAR_MIN
WCHAR_MAX
WINT_MIN
WINT_MAXINTN_C(value)
UINTN_C(value)
INTMAX_C(value)
UINTMAX_C(value)

B.18 Input/output <stdio.h>
size_tFILE
fpos_tNULL_IOFBF_IOLBF_IONBFBUFSIZEOF
FOPEN_MAXFILENAME_MAX
L_tmpnam
SEEK_CURSEEK_END
SEEK_SETTMP_MAXstderrstdin
stdoutint remove(const char *filename);
int rename(const char *old, const char *new);
FILE *tmpfile(void);char *tmpnam(char *s);
int fclose(FILE *stream);
int fflush(FILE *stream);
FILE *fopen(const char * restrict filename,const char * restrict mode);
FILE *freopen(const char * restrict filename,const char * restrict mode,
FILE * restrict stream);void setbuf(FILE * restrict stream,char * restrict buf);§B.18

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int setvbuf(FILE * restrict stream,char * restrict buf,
int mode, size_t size);
int fprintf(FILE * restrict stream,
const char * restrict format, ...);
int fscanf(FILE * restrict stream,
const char * restrict format, ...);
int printf(const char * restrict format, ...);
int scanf(const char * restrict format, ...);
int snprintf(char * restrict s, size_t n,
const char * restrict format, ...);
int sprintf(char * restrict s,
const char * restrict format, ...);
int sscanf(const char * restrict s,
const char * restrict format, ...);
int vfprintf(FILE * restrict stream,
const char * restrict format, va_list arg);
int vfscanf(FILE * restrict stream,
const char * restrict format, va_list arg);
int vprintf(const char * restrict format, va_list arg);
int vscanf(const char * restrict format, va_list arg);
int vsnprintf(char * restrict s, size_t n,
const char * restrict format, va_list arg);
int vsprintf(char * restrict s,
const char * restrict format, va_list arg);
int vsscanf(const char * restrict s,
const char * restrict format, va_list arg);
int fgetc(FILE *stream);char *fgets(char * restrict s, int n,
FILE * restrict stream);
int fputc(int c, FILE *stream);
int fputs(const char * restrict s,
FILE * restrict stream);int getc(FILE *stream);int getchar(void);char *gets(char *s);
int putc(int c, FILE *stream);int putchar(int c);
int puts(const char *s);
int ungetc(int c, FILE *stream);

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size_t fread(void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);size_t fwrite(const void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
int fgetpos(FILE * restrict stream,
fpos_t * restrict pos);
int fseek(FILE *stream, long int offset, int whence);
int fsetpos(FILE *stream, const fpos_t *pos);long int ftell(FILE *stream);void rewind(FILE *stream);void clearerr(FILE *stream);
int feof(FILE *stream);
int ferror(FILE *stream);void perror(const char *s);B.19 General utilities <stdlib.h>size_twchar_tdiv_tldiv_tlldiv_t
NULL

EXIT_FAILURE
EXIT_SUCCESSRAND_MAX

MB_CUR_MAX

double atof(const char *nptr);
int atoi(const char *nptr);
long int atol(const char *nptr);
long long int atoll(const char *nptr);
double strtod(const char * restrict nptr,
char ** restrict endptr);
float strtof(const char * restrict nptr,
char ** restrict endptr);
long double strtold(const char * restrict nptr,
char ** restrict endptr);
long int strtol(const char * restrict nptr,
char ** restrict endptr, int base);long long int strtoll(const char * restrict nptr,
char ** restrict endptr, int base);
unsigned long int strtoul(
const char * restrict nptr,
char ** restrict endptr, int base);§B.19

Library summary

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unsigned long long int strtoull(const char * restrict nptr,
char ** restrict endptr, int base);
int rand(void);void srand(unsigned int seed);void *calloc(size_t nmemb, size_t size);
void free(void *ptr);
void *malloc(size_t size);
void *realloc(void *ptr, size_t size);
void abort(void);
int atexit(void (*func)(void));void exit(int status);
void _Exit(int status);char *getenv(const char *name);
int system(const char *string);
void *bsearch(const void *key, const void *base,size_t nmemb, size_t size,int (*compar)(const void *, const void *));
void qsort(void *base, size_t nmemb, size_t size,int (*compar)(const void *, const void *));
int abs(int j);long int labs(long int j);long long int llabs(long long int j);
div_t div(int numer, int denom);
ldiv_t ldiv(long int numer, long int denom);
lldiv_t lldiv(long long int numer,
long long int denom);
int mblen(const char *s, size_t n);
int mbtowc(wchar_t * restrict pwc,
const char * restrict s, size_t n);
int wctomb(char *s, wchar_t wchar);size_t mbstowcs(wchar_t * restrict pwcs,
const char * restrict s, size_t n);size_t wcstombs(char * restrict s,
const wchar_t * restrict pwcs, size_t n);

432

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B.20 String handling <string.h>size_tNULL
void *memcpy(void * restrict s1,
const void * restrict s2, size_t n);void *memmove(void *s1, const void *s2, size_t n);char *strcpy(char * restrict s1,
const char * restrict s2);
char *strncpy(char * restrict s1,
const char * restrict s2, size_t n);char *strcat(char * restrict s1,
const char * restrict s2);
char *strncat(char * restrict s1,
const char * restrict s2, size_t n);
int memcmp(const void *s1, const void *s2, size_t n);
int strcmp(const char *s1, const char *s2);
int strcoll(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n);size_t strxfrm(char * restrict s1,
const char * restrict s2, size_t n);void *memchr(const void *s, int c, size_t n);char *strchr(const char *s, int c);size_t strcspn(const char *s1, const char *s2);
char *strpbrk(const char *s1, const char *s2);
char *strrchr(const char *s, int c);size_t strspn(const char *s1, const char *s2);
char *strstr(const char *s1, const char *s2);
char *strtok(char * restrict s1,
const char * restrict s2);
void *memset(void *s, int c, size_t n);char *strerror(int errnum);size_t strlen(const char *s);

§B.20

Library summary

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B.21 Type-generic math <tgmath.h>
acos
asin
atan
acosh
asinh
atanh
cos
sin
tan
cosh
sinh
tanh
exp
log
pow

sqrt
fabs
atan2
cbrt
ceil
copysign
erf
erfc
exp2
expm1
fdim
floor
fma
fmax
fmin

fmod
frexp
hypot
ilogb
ldexp
lgammallrintllround
log10
log1p
log2
logb
lrint
lroundnearbyint

nextafter
nexttowardremainder
remquorint
round
scalbnscalblntgamma
trunc
carg
cimag
conj
cproj
creal

B.22 Date and time <time.h>
NULL
CLOCKS_PER_SEC

size_tclock_ttime_tstruct tm

clock_t clock(void);
double difftime(time_t time1, time_t time0);
time_t mktime(struct tm *timeptr);
time_t time(time_t *timer);char *asctime(const struct tm *timeptr);
char *ctime(const time_t *timer);struct tm *gmtime(const time_t *timer);struct tm *localtime(const time_t *timer);size_t strftime(char * restrict s,size_t maxsize,
const char * restrict format,
const struct tm * restrict timeptr);

434

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B.23 Extended multibyte/wide character utilities <wchar.h>wchar_tsize_tmbstate_t

wint_tstruct tm
NULL

WCHAR_MAX
WCHAR_MIN
WEOF

int fwprintf(FILE * restrict stream,
const wchar_t * restrict format, ...);
int fwscanf(FILE * restrict stream,
const wchar_t * restrict format, ...);
int swprintf(wchar_t * restrict s, size_t n,
const wchar_t * restrict format, ...);
int swscanf(const wchar_t * restrict s,
const wchar_t * restrict format, ...);
int vfwprintf(FILE * restrict stream,
const wchar_t * restrict format, va_list arg);
int vfwscanf(FILE * restrict stream,
const wchar_t * restrict format, va_list arg);
int vswprintf(wchar_t * restrict s, size_t n,
const wchar_t * restrict format, va_list arg);
int vswscanf(const wchar_t * restrict s,
const wchar_t * restrict format, va_list arg);
int vwprintf(const wchar_t * restrict format,
va_list arg);
int vwscanf(const wchar_t * restrict format,
va_list arg);
int wprintf(const wchar_t * restrict format, ...);
int wscanf(const wchar_t * restrict format, ...);
wint_t fgetwc(FILE *stream);wchar_t *fgetws(wchar_t * restrict s, int n,
FILE * restrict stream);
wint_t fputwc(wchar_t c, FILE *stream);
int fputws(const wchar_t * restrict s,
FILE * restrict stream);
int fwide(FILE *stream, int mode);
wint_t getwc(FILE *stream);
wint_t getwchar(void);
wint_t putwc(wchar_t c, FILE *stream);
wint_t putwchar(wchar_t c);
wint_t ungetwc(wint_t c, FILE *stream);§B.23

Library summary

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double wcstod(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
float wcstof(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
long double wcstold(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
long int wcstol(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);long long int wcstoll(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
unsigned long int wcstoul(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
unsigned long long int wcstoull(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);wchar_t *wcscpy(wchar_t * restrict s1,
const wchar_t * restrict s2);
wchar_t *wcsncpy(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);wchar_t *wmemcpy(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
size_t n);wchar_t *wcscat(wchar_t * restrict s1,
const wchar_t * restrict s2);
wchar_t *wcsncat(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);
int wcscmp(const wchar_t *s1, const wchar_t *s2);
int wcscoll(const wchar_t *s1, const wchar_t *s2);
int wcsncmp(const wchar_t *s1, const wchar_t *s2,
size_t n);size_t wcsxfrm(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);
int wmemcmp(const wchar_t *s1, const wchar_t *s2,
size_t n);wchar_t *wcschr(const wchar_t *s, wchar_t c);size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2); ∗wchar_t *wcsrchr(const wchar_t *s, wchar_t c);size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);

436

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wchar_t *wcstok(wchar_t * restrict s1,
const wchar_t * restrict s2,
wchar_t ** restrict ptr);
wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);size_t wcslen(const wchar_t *s);wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);size_t wcsftime(wchar_t * restrict s, size_t maxsize,
const wchar_t * restrict format,
const struct tm * restrict timeptr);
wint_t btowc(int c);
int wctob(wint_t c);
int mbsinit(const mbstate_t *ps);size_t mbrlen(const char * restrict s, size_t n,
mbstate_t * restrict ps);size_t mbrtowc(wchar_t * restrict pwc,
const char * restrict s, size_t n,
mbstate_t * restrict ps);size_t wcrtomb(char * restrict s, wchar_t wc,
mbstate_t * restrict ps);size_t mbsrtowcs(wchar_t * restrict dst,
const char ** restrict src, size_t len,mbstate_t * restrict ps);size_t wcsrtombs(char * restrict dst,
const wchar_t ** restrict src, size_t len,mbstate_t * restrict ps);

B.24 Wide character classification and mapping utilities <wctype.h>
wint_twctrans_t

wctype_t

WEOF

int iswalnum(wint_t wc);
int iswalpha(wint_t wc);
int iswblank(wint_t wc);
int iswcntrl(wint_t wc);
int iswdigit(wint_t wc);
int iswgraph(wint_t wc);
int iswlower(wint_t wc);
int iswprint(wint_t wc);
int iswpunct(wint_t wc);
int iswspace(wint_t wc);
int iswupper(wint_t wc);
int iswxdigit(wint_t wc);
int iswctype(wint_t wc, wctype_t desc);§B.24

Library summary

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wctype_t wctype(const char *property);
wint_t towlower(wint_t wc);
wint_t towupper(wint_t wc);
wint_t towctrans(wint_t wc, wctrans_t desc);
wctrans_t wctrans(const char *property);438

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Annex C
(informative)
Sequence points
1

The following are the sequence points described in 5.1.2.3:— The call to a function, after the arguments have been evaluated (6.5.2.2).
— The end of the first operand of the following operators: logical AND && (6.5.13);
logical OR || (6.5.14); conditional ? (6.5.15); comma , (6.5.17).
— The end of a full declarator: declarators (6.7.5);— The end of a full expression: an initializer (6.7.8); the expression in an expression
statement (6.8.3); the controlling expression of a selection statement (if or switch)(6.8.4); the controlling expression of a while or do statement (6.8.5); each of theexpressions of a for statement (6.8.5.3); the expression in a return statement(6.8.6.4).
— Immediately before a library function returns (7.1.4).
— After the actions associated with each formatted input/output function conversion
specifier (7.19.6, 7.24.2).
— Immediately before and immediately after each call to a comparison function, andalso between any call to a comparison function and any movement of the objects
passed as arguments to that call (7.20.5).

§C

Sequence points

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Annex D(normative)
Universal character names for identifiers
1This clause lists the hexadecimal code values that are valid in universal character names
in identifiers.

2This table is reproduced unchanged from ISO/IEC TR 10176:1998, produced by ISO/IEC
JTC 1/SC 22/WG 20, except for the omission of ranges that are part of the basic character
sets.
Latin:

00AA, 00BA, 00C0−00D6, 00D8−00F6, 00F8−01F5, 01FA−0217,
0250−02A8, 1E00−1E9B, 1EA0−1EF9, 207F

Greek:

0386, 0388−038A, 038C, 038E−03A1, 03A3−03CE, 03D0−03D6,
03DA, 03DC, 03DE, 03E0, 03E2−03F3, 1F00−1F15, 1F18−1F1D,
1F20−1F45, 1F48−1F4D, 1F50−1F57, 1F59, 1F5B, 1F5D,
1F5F−1F7D, 1F80−1FB4, 1FB6−1FBC, 1FC2−1FC4, 1FC6−1FCC,
1FD0−1FD3, 1FD6−1FDB, 1FE0−1FEC, 1FF2−1FF4, 1FF6−1FFC

Cyrillic:

0401−040C, 040E−044F, 0451−045C, 045E−0481, 0490−04C4,
04C7−04C8, 04CB−04CC, 04D0−04EB, 04EE−04F5, 04F8−04F9

Armenian:

0531−0556, 0561−0587

Hebrew:

05B0−05B9,
05F0−05F2

Arabic:0621−063A, 0640−0652, 0670−06B7, 06BA−06BE, 06C0−06CE,
06D0−06DC, 06E5−06E8, 06EA−06ED

Devanagari:0901−0903, 0905−0939, 093E−094D, 0950−0952, 0958−0963

Bengali:0981−0983, 0985−098C, 098F−0990, 0993−09A8, 09AA−09B0,
09B2, 09B6−09B9, 09BE−09C4, 09C7−09C8, 09CB−09CD,
09DC−09DD, 09DF−09E3, 09F0−09F1

Gurmukhi:

0A02, 0A05−0A0A, 0A0F−0A10, 0A13−0A28, 0A2A−0A30,
0A32−0A33, 0A35−0A36, 0A38−0A39, 0A3E−0A42, 0A47−0A48,
0A4B−0A4D, 0A59−0A5C, 0A5E, 0A74

Gujarati:

0A81−0A83, 0A85−0A8B, 0A8D, 0A8F−0A91, 0A93−0AA8,
0AAA−0AB0,
0AB2−0AB3,
0AB5−0AB9,
0ABD−0AC5,
0AC7−0AC9, 0ACB−0ACD, 0AD0, 0AE0

Oriya:

0B01−0B03, 0B05−0B0C, 0B0F−0B10, 0B13−0B28, 0B2A−0B30,
0B32−0B33, 0B36−0B39, 0B3E−0B43, 0B47−0B48, 0B4B−0B4D,

440

05BB−05BD,

05BF,

05C1−05C2,

Universal character names for identifiers

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0B5C−0B5D, 0B5F−0B61
Tamil:

0B82−0B83, 0B85−0B8A, 0B8E−0B90, 0B92−0B95, 0B99−0B9A,
0B9C, 0B9E−0B9F, 0BA3−0BA4, 0BA8−0BAA, 0BAE−0BB5,
0BB7−0BB9, 0BBE−0BC2, 0BC6−0BC8, 0BCA−0BCD

Telugu:0C01−0C03, 0C05−0C0C, 0C0E−0C10, 0C12−0C28, 0C2A−0C33,
0C35−0C39, 0C3E−0C44, 0C46−0C48, 0C4A−0C4D, 0C60−0C61

Kannada:0C82−0C83, 0C85−0C8C, 0C8E−0C90, 0C92−0CA8, 0CAA−0CB3,
0CB5−0CB9, 0CBE−0CC4, 0CC6−0CC8, 0CCA−0CCD, 0CDE,
0CE0−0CE1

Malayalam:

0D02−0D03, 0D05−0D0C, 0D0E−0D10, 0D12−0D28, 0D2A−0D39,
0D3E−0D43, 0D46−0D48, 0D4A−0D4D, 0D60−0D61

Thai:

0E01−0E3A, 0E40−0E5B

Lao:

0E81−0E82, 0E84, 0E87−0E88, 0E8A, 0E8D, 0E94−0E97,
0E99−0E9F,
0EA1−0EA3,
0EA5,
0EA7,
0EAA−0EAB,
0EAD−0EAE, 0EB0−0EB9, 0EBB−0EBD, 0EC0−0EC4, 0EC6,
0EC8−0ECD, 0EDC−0EDD

Tibetan:

0F00, 0F18−0F19, 0F35, 0F37, 0F39, 0F3E−0F47, 0F49−0F69,
0F71−0F84, 0F86−0F8B, 0F90−0F95, 0F97, 0F99−0FAD,
0FB1−0FB7, 0FB9

Georgian:

10A0−10C5, 10D0−10F6

Hiragana:

3041−3093, 309B−309C

Katakana:

30A1−30F6, 30FB−30FC

Bopomofo:3105−312CCJK Unified Ideographs: 4E00−9FA5
Hangul:AC00−D7A3

Digits:0660−0669, 06F0−06F9, 0966−096F, 09E6−09EF, 0A66−0A6F,
0AE6−0AEF, 0B66−0B6F, 0BE7−0BEF, 0C66−0C6F, 0CE6−0CEF,
0D66−0D6F, 0E50−0E59, 0ED0−0ED9, 0F20−0F33

Special characters: 00B5, 00B7, 02B0−02B8, 02BB, 02BD−02C1, 02D0−02D1,
02E0−02E4, 037A, 0559, 093D, 0B3D, 1FBE, 203F−2040, 2102,
2107, 210A−2113, 2115, 2118−211D, 2124, 2126, 2128, 212A−2131,
2133−2138, 2160−2182, 3005−3007, 3021−3029§D

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Annex E
(informative)
Implementation limits
1

The contents of the header <limits.h> are given below, in alphabetical order. The
minimum magnitudes shown shall be replaced by implementation-defined magnitudes
with the same sign. The values shall all be constant expressions suitable for use in #if
preprocessing directives. The components are described further in 5.2.4.2.1.
#define CHAR_BIT#define CHAR_MAX#define CHAR_MIN#define INT_MAX#define INT_MIN#define LONG_MAX#define LONG_MIN#define LLONG_MAX#define LLONG_MIN#define MB_LEN_MAX#define SCHAR_MAX#define SCHAR_MIN#define SHRT_MAX#define SHRT_MIN#define UCHAR_MAX#define USHRT_MAX#define UINT_MAX#define ULONG_MAX#define ULLONG_MAX

8
UCHAR_MAX or SCHAR_MAX
0 or SCHAR_MIN+32767-32767+2147483647-2147483647+9223372036854775807-9223372036854775807
1
+127
-127
+32767-32767
255
65535
65535
4294967295
18446744073709551615

2

The contents of the header <float.h> are given below. All integer values, except
FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing
directives; all floating values shall be constant expressions. The components aredescribed further in 5.2.4.2.2.

3

The values given in the following list shall be replaced by implementation-defined
expressions:#define FLT_EVAL_METHOD#define FLT_ROUNDS

4

The values given in the following list shall be replaced by implementation-definedconstant expressions that are greater or equal in magnitude (absolute value) to thoseshown, with the same sign:
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#define DBL_DIG#define DBL_MANT_DIG#define DBL_MAX_10_EXP#define DBL_MAX_EXP#define DBL_MIN_10_EXP#define DBL_MIN_EXP#define DECIMAL_DIG#define FLT_DIG#define FLT_MANT_DIG#define FLT_MAX_10_EXP#define FLT_MAX_EXP#define FLT_MIN_10_EXP#define FLT_MIN_EXP#define FLT_RADIX#define LDBL_DIG#define LDBL_MANT_DIG#define LDBL_MAX_10_EXP#define LDBL_MAX_EXP#define LDBL_MIN_10_EXP#define LDBL_MIN_EXP
5

10
+37
-37
10
6
+37
-37
2
10
+37
-37

The values given in the following list shall be replaced by implementation-definedconstant expressions with values that are greater than or equal to those shown:#define DBL_MAX#define FLT_MAX#define LDBL_MAX

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1E+37
1E+37
1E+37

The values given in the following list shall be replaced by implementation-definedconstant expressions with (positive) values that are less than or equal to those shown:#define DBL_EPSILON#define DBL_MIN#define FLT_EPSILON#define FLT_MIN#define LDBL_EPSILON#define LDBL_MIN§E

Implementation limits

1E-9
1E-37
1E-5
1E-37
1E-9
1E-37

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Annex F(normative)
IEC 60559 floating-point arithmetic
F.1 Introduction
1

This annex specifies C language support for the IEC 60559 floating-point standard. The
IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for
microprocessor systems, second edition (IEC 60559:1989), previously designated
IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic(ANSI/IEEE 754−1985). IEEE Standard for Radix-Independent Floating-Point
Arithmetic (ANSI/IEEE 854−1987) generalizes the binary standard to remove
dependencies on radix and word length. IEC 60559 generally refers to the floating-point
standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation thatdefines _ _STDC_IEC_559_ _ shall conform to the specifications in this annex. Wherea binding between the C language and IEC 60559 is indicated, the IEC 60559-specified
behavior is adopted by reference, unless stated otherwise.

F.2 Types
1

The C floating types match the IEC 60559 formats as follows:— The float type matches the IEC 60559 single format.
— The double type matches the IEC 60559 double format.
— The long double type matches an IEC 60559 extended format,307) else a
non-IEC 60559 extended format, else the IEC 60559 double format.
Any non-IEC 60559 extended format used for the long double type shall have more
precision than IEC 60559 double and at least the range of IEC 60559 double.308)
Recommended practice2

The long double type should match an IEC 60559 extended format.

307) ‘‘Extended’’ is IEC 60559’s double-extended data format. Extended refers to both the common 80-bit
and quadruple 128-bit IEC 60559 formats.
308) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include
all double values.

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F.2.1 Infinities, signed zeros, and NaNs
1

This specification does not define the behavior of signaling NaNs.309) It generally uses
the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nanfunctions in <math.h> provide designations for IEC 60559 NaNs and infinities.

F.3 Operators and functions
1

C operators and functions provide IEC 60559 required and recommended facilities aslisted below.
— The +, −, *, and / operators provide the IEC 60559 add, subtract, multiply, anddivide operations.
— The sqrt functions in <math.h> provide the IEC 60559 square root operation.
— The remainder functions in <math.h> provide the IEC 60559 remainder
operation. The remquo functions in <math.h> provide the same operation but
with additional information.
— The rint functions in <math.h> provide the IEC 60559 operation that rounds a
floating-point number to an integer value (in the same precision). The nearbyint
functions in <math.h> provide the nearbyinteger function recommended in the
Appendix to ANSI/IEEE 854.
— The conversions for floating types provide the IEC 60559 conversions between
floating-point precisions.
— The conversions from integer to floating types provide the IEC 60559 conversions
from integer to floating point.
— The conversions from floating to integer types provide IEC 60559-like conversions
but always round toward zero.
— The lrint and llrint functions in <math.h> provide the IEC 60559
conversions, which honor the directed rounding mode, from floating point to thelong int and long long int integer formats. The lrint and llrint
functions can be used to implement IEC 60559 conversions from floating to otherinteger formats.
— The translation time conversion of floating constants and the strtod, strtof,
strtold, fprintf, fscanf, and related library functions in <stdlib.h>,<stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The
strtold function in <stdlib.h> provides the conv function recommended in the
Appendix to ANSI/IEEE 854.
309) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) aresufficient for closure of the arithmetic.

§F.3

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WG14/N1256— The relational and equality operators provide IEC 60559 comparisons. IEC 60559
identifies a need for additional comparison predicates to facilitate writing code that
accounts for NaNs. The comparison macros (isgreater, isgreaterequal,
isless, islessequal, islessgreater, and isunordered) in <math.h>
supplement the language operators to address this need. The islessgreater andisunordered macros provide respectively a quiet version of the <> predicate andthe unordered predicate recommended in the Appendix to IEC 60559.
— The feclearexcept, feraiseexcept, and fetestexcept functions in<fenv.h> provide the facility to test and alter the IEC 60559 floating-point
exception status flags. The fegetexceptflag and fesetexceptflag
functions in <fenv.h> provide the facility to save and restore all five status flags at
one time. These functions are used in conjunction with the type fexcept_t and thefloating-point
exception
macros(FE_INEXACT,
FE_DIVBYZERO,
FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>.
— The fegetround and fesetround functions in <fenv.h> provide the facility
to select among the IEC 60559 directed rounding modes represented by the rounding
direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are theIEC 60559 directed rounding modes.
— The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in<fenv.h> provide a facility to manage the floating-point environment, comprising
the IEC 60559 status flags and control modes.
— The copysign functions in <math.h> provide the copysign function
recommended in the Appendix to IEC 60559.
— The unary minus (−) operator provides the minus (−) operation recommended in the
Appendix to IEC 60559.
— The scalbn and scalbln functions in <math.h> provide the scalb function
recommended in the Appendix to IEC 60559.
— The logb functions in <math.h> provide the logb function recommended in the
Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854.
— The nextafter and nexttoward functions in <math.h> provide the nextafter
function recommended in the Appendix to IEC 60559 (but with a minor change tobetter handle signed zeros).
— The isfinite macro in <math.h> provides the finite function recommended in
the Appendix to IEC 60559.
— The isnan macro in <math.h> provides the isnan function recommended in the
Appendix to IEC 60559.
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ISO/IEC 9899:TC3— The signbit macro and the fpclassify macro in <math.h>, used inconjunction with the number classification macros (FP_NAN, FP_INFINITE,FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class
function recommended in the Appendix to IEC 60559 (except that the classification
macros defined in 7.12.3 do not distinguish signaling from quiet NaNs).

F.4 Floating to integer conversion
1

If the floating value is infinite or NaN or if the integral part of the floating value exceeds
the range of the integer type, then the ‘‘invalid’’ floating-point exception is raised and theresulting value is unspecified. Whether conversion of non-integer floating values whose
integral part is within the range of the integer type raises the ‘‘inexact’’ floating-point
exception is unspecified.310)

F.5 Binary-decimal conversion
1

Conversion from the widest supported IEC 60559 format to decimal with
DECIMAL_DIG digits and back is the identity function.311)

2

Conversions involving IEC 60559 formats follow all pertinent recommended practice. In
particular, conversion between any supported IEC 60559 format and decimal with
DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current
rounding mode), which assures that conversion from the widest supported IEC 60559
format to decimal with DECIMAL_DIG digits and back is the identity function.

3

Functions such as strtod that convert character sequences to floating types honor therounding direction. Hence, if the rounding direction might be upward or downward, theimplementation cannot convert a minus-signed sequence by negating the converted
unsigned sequence.

310) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer
conversions raise the ‘‘inexact’’ floating-point exception for non-integer in-range values. In thosecases where it matters, library functions can be used to effect such conversions with or without raisingthe ‘‘inexact’’ floating-point exception. See rint, lrint, llrint, and nearbyint in<math.h>.
311) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported,
DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest
IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and
DBL_DIG are 18 and 15, respectively, for these formats.)§F.5

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F.6 Contracted expressions
1

A contracted expression treats infinities, NaNs, signed zeros, subnormals, and therounding directions in a manner consistent with the basic arithmetic operations coveredby IEC 60559.
Recommended practice2

A contracted expression should raise floating-point exceptions in a manner generally
consistent with the basic arithmetic operations. A contracted expression should deliver
the same value as its uncontracted counterpart, else should be correctly rounded (once).

F.7 Floating-point environment
1

The floating-point environment defined in <fenv.h> includes the IEC 60559 floatingpoint exception status flags and directed-rounding control modes. It includes also
IEC 60559 dynamic rounding precision and trap enablement modes, if theimplementation supports them.312)

F.7.1 Environment management1

IEC 60559 requires that floating-point operations implicitly raise floating-point exception
status flags, and that rounding control modes can be set explicitly to affect result values offloating-point operations. When the state for the FENV_ACCESS pragma (defined in<fenv.h>) is ‘‘on’’, these changes to the floating-point state are treated as side effects
which respect sequence points.313)

F.7.2 Translation
1

During translation the IEC 60559 default modes are in effect:— The rounding direction mode is rounding to nearest.
— The rounding precision mode (if supported) is set so that results are not shortened.
— Trapping or stopping (if supported) is disabled on all floating-point exceptions.
Recommended practice2

The implementation should produce a diagnostic message for each translation-time312) This specification does not require dynamic rounding precision nor trap enablement modes.
313) If the state for the FENV_ACCESS pragma is ‘‘off’’, the implementation is free to assume the floatingpoint control modes will be the default ones and the floating-point status flags will not be tested,which allows certain optimizations (see F.8).

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floating-point exception, other than ‘‘inexact’’;314) the implementation should thenproceed with the translation of the program.

F.7.3 Execution
1

At program startup the floating-point environment is initialized as prescribed by
IEC 60559:— All floating-point exception status flags are cleared.
— The rounding direction mode is rounding to nearest.
— The dynamic rounding precision mode (if supported) is set so that results are not
shortened.
— Trapping or stopping (if supported) is disabled on all floating-point exceptions.

F.7.4 Constant expressions
1

An arithmetic constant expression of floating type, other than one in an initializer for an
object that has static storage duration, is evaluated (as if) during execution; thus, it isaffected by any operative floating-point control modes and raises floating-point
exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragmais ‘‘on’’).315)

2

EXAMPLE#include <fenv.h>#pragma STDC FENV_ACCESS ON
void f(void){
float w[] = { 0.0/0.0 }; // raises an exception
static float x = 0.0/0.0; // does not raise an exception
float y = 0.0/0.0;// raises an exception
double z = 0.0/0.0;// raises an exception/* ... */}3

For the static initialization, the division is done at translation time, raising no (execution-time) floatingpoint exceptions. On the other hand, for the three automatic initializations the invalid division occurs at314) As floating constants are converted to appropriate internal representations at translation time, theirconversion is subject to default rounding modes and raises no execution-time floating-point exceptions(even where the state of the FENV_ACCESS pragma is ‘‘on’’). Library functions, for example
strtod, provide execution-time conversion of numeric strings.
315) Where the state for the FENV_ACCESS pragma is ‘‘on’’, results of inexact expressions like 1.0/3.0
are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve theefficiency of translation-time evaluation through static initialization, such as
const static double one_third = 1.0/3.0;§F.7.4

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execution time.

F.7.5 Initialization
1

All computation for automatic initialization is done (as if) at execution time; thus, it isaffected by any operative modes and raises floating-point exceptions as required by
IEC 60559 (provided the state for the FENV_ACCESS pragma is ‘‘on’’). All computation
for initialization of objects that have static storage duration is done (as if) at translation
time.

2

EXAMPLE#include <fenv.h>#pragma STDC FENV_ACCESS ON
void f(void){
float u[] = { 1.1e75 }; // raises exceptions
static float v = 1.1e75; // does not raise exceptions
float w = 1.1e75;// raises exceptions
double x = 1.1e75;// may raise exceptions
float y = 1.1e75f;// may raise exceptions
long double z = 1.1e75; // does not raise exceptions/* ... */}3

The static initialization of v raises no (execution-time) floating-point exceptions because its computation isdone at translation time. The automatic initialization of u and w require an execution-time conversion to
float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializationsof x and y entail execution-time conversion; however, in some expression evaluation methods, theconversions is not to a narrower format, in which case no floating-point exception is raised.316) The
automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floatingpoint exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f totheir internal representations occur at translation time in all cases.

316) Use of float_t and double_t variables increases the likelihood of translation-time computation.
For example, the automatic initialization
double_t x = 1.1e75;
could be done at translation time, regardless of the expression evaluation method.

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F.7.6 Changing the environment
1

Operations defined in 6.5 and functions and macros defined for the standard libraries
change floating-point status flags and control modes just as indicated by their
specifications (including conformance to IEC 60559). They do not change flags or modes(so as to be detectable by the user) in any other cases.

2

If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559
valid coincident floating-point exceptions for atomic operations (namely ‘‘overflow’’ and‘‘inexact’’, or ‘‘underflow’’ and ‘‘inexact’’), then ‘‘overflow’’ or ‘‘underflow’’ is raised
before ‘‘inexact’’.

F.8 Optimization
1

This section identifies code transformations that might subvert IEC 60559-specified
behavior, and others that do not.

F.8.1 Global transformations
1

Floating-point arithmetic operations and external function calls may entail side effects
which optimization shall honor, at least where the state of the FENV_ACCESS pragma is‘‘on’’. The flags and modes in the floating-point environment may be regarded as global
variables; floating-point operations (+, *, etc.) implicitly read the modes and write theflags.

2

Concern about side effects may inhibit code motion and removal of seemingly uselesscode. For example, in#include <fenv.h>#pragma STDC FENV_ACCESS ON
void f(double x){/* ... */for (i = 0; i < n; i++) x + 1;/* ... */}x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop
body might not execute (maybe 0 ≥ n), x + 1 cannot be moved out of the loop. (Ofcourse these optimizations are valid if the implementation can rule out the nettlesome
cases.)

3This specification does not require support for trap handlers that maintain information
about the order or count of floating-point exceptions. Therefore, between function calls,
floating-point exceptions need not be precise: the actual order and number of occurrencesof floating-point exceptions (> 1) may vary from what the source code expresses. Thus,
the preceding loop could be treated as§F.8.1

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if (0 < n) x + 1;

F.8.2 Expression transformations
1

x / 2 ↔ x * 0.5

Although similar transformations involving inexact
constants generally do not yield numerically equivalent
expressions, if the constants are exact then suchtransformations can be made on IEC 60559 machines
and others that round perfectly.

1 * x and x / 1 → x

The expressions 1 * x, x / 1, and x are equivalent(on IEC 60559 machines, among others).317)

x / x → 1.0

The expressions x / x and 1.0 are not equivalent if x
can be zero, infinite, or NaN.

x − y ↔ x + (−y)

The expressions x − y, x + (−y), and (−y) + x
are equivalent (on IEC 60559 machines, among others).

x − y ↔ −(y − x)

The expressions x − y and −(y − x) are notequivalent because 1 − 1 is +0 but −(1 − 1) is −0 (in thedefault rounding direction).318)

x − x → 0.0

The expressions x − x and 0.0 are not equivalent if
x is a NaN or infinite.

0 * x → 0.0

The expressions 0 * x and 0.0 are not equivalent if
x is a NaN, infinite, or −0.

x + 0→x

The expressions x + 0 and x are not equivalent if x is−0, because (−0) + (+0) yields +0 (in the default
rounding direction), not −0.

x − 0→x(+0) − (+0) yields −0 when rounding is downward(toward −∞), but +0 otherwise, and (−0) − (+0) always
yields −0; so, if the state of the FENV_ACCESS pragmais ‘‘off’’, promising default rounding, then theimplementation can replace x − 0 by x, even if x317) Strict support for signaling NaNs — not required by this specification — would invalidate these andother transformations that remove arithmetic operators.
318) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
Examples include:
1/(1/ ± ∞) is ± ∞andconj(csqrt(z)) is csqrt(conj(z)),
for complex z.

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might be zero.
−x ↔ 0 − x

The expressions −x and 0 − x are not equivalent if x
is +0, because −(+0) yields −0, but 0 − (+0) yields +0(unless rounding is downward).

F.8.3 Relational operators
1

x != x → false

The statement x != x is true if x is a NaN.

x == x → true

The statement x == x is false if x is a NaN.

x < y → isless(x,y)(and similarly for <=, >, >=) Though numericallyequal, these expressions are not equivalent because ofside effects when x or y is a NaN and the state of the
FENV_ACCESS pragma is ‘‘on’’. This transformation,
which would be desirable if extra code were required tocause the ‘‘invalid’’ floating-point exception for
unordered cases, could be performed provided the stateof the FENV_ACCESS pragma is ‘‘off’’.

The sense of relational operators shall be maintained. This includes handling unorderedcases as expressed by the source code.
2

EXAMPLE// calls g and raises ‘‘invalid’’ if a and b are unorderedif (a < b)
f();
else
g();
is not equivalent to// calls f and raises ‘‘invalid’’ if a and b are unorderedif (a >= b)
g();
else
f();
nor to// calls f without raising ‘‘invalid’’ if a and b are unordered
if (isgreaterequal(a,b))
g();
else
f();
nor, unless the state of the FENV_ACCESS pragma is ‘‘off’’, to§F.8.3

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WG14/N1256// calls g without raising ‘‘invalid’’ if a and b are unordered
if (isless(a,b))
f();
else
g();
but is equivalent toif (!(a < b))
g();
else
f();

F.8.4 Constant arithmetic
1

The implementation shall honor floating-point exceptions raised by execution-time
constant arithmetic wherever the state of the FENV_ACCESS pragma is ‘‘on’’. (See F.7.4
and F.7.5.) An operation on constants that raises no floating-point exception can befolded during translation, except, if the state of the FENV_ACCESS pragma is ‘‘on’’, afurther check is required to assure that changing the rounding direction to downward does
not alter the sign of the result,319) and implementations that support dynamic rounding
precision modes shall assure further that the result of the operation raises no floatingpoint exception when converted to the semantic type of the operation.

F.9 Mathematics <math.h>1This subclause contains specifications of <math.h> facilities that are particularly suitedfor IEC 60559 implementations.

2

The Standard C macro HUGE_VAL and its float and long double analogs,
HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive
infinities.

3

Special cases for functions in <math.h> are covered directly or indirectly by
IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The
other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and(provided the state of the FENV_ACCESS pragma is ‘‘on’’) the floating-point status flags
in a manner consistent with the basic arithmetic operations covered by IEC 60559.

4

The expression math_errhandling & MATH_ERREXCEPT shall evaluate to anonzero value.

5

The ‘‘invalid’’ and ‘‘divide-by-zero’’ floating-point exceptions are raised as specified insubsequent subclauses of this annex.

6

The ‘‘overflow’’ floating-point exception is raised whenever an infinity — or, because ofrounding direction, a maximal-magnitude finite number — is returned in lieu of a value319) 0 − 0 yields −0 instead of +0 just when the rounding direction is downward.

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whose magnitude is too large.
7

The ‘‘underflow’’ floating-point exception is raised whenever a result is tiny (essentiallysubnormal or zero) and suffers loss of accuracy.320)

8

Whether or when library functions raise the ‘‘inexact’’ floating-point exception isunspecified, unless explicitly specified otherwise.

9

Whether or when library functions raise an undeserved ‘‘underflow’’ floating-point
exception is unspecified.321) Otherwise, as implied by F.7.6, the <math.h> functions do
not raise spurious floating-point exceptions (detectable by the user), other than the‘‘inexact’’ floating-point exception.

10

Whether the functions honor the rounding direction mode is implementation-defined,
unless explicitly specified otherwise.

11

Functions with a NaN argument return a NaN result and raise no floating-point exception,
except where stated otherwise.

12

The specifications in the following subclauses append to the definitions in <math.h>.
For families of functions, the specifications apply to all of the functions even though only
the principal function is shown. Unless otherwise specified, where the symbol ‘‘±’’occurs in both an argument and the result, the result has the same sign as the argument.
Recommended practice13

If a function with one or more NaN arguments returns a NaN result, the result should be
the same as one of the NaN arguments (after possible type conversion), except perhaps
for the sign.

F.9.1 Trigonometric functions
F.9.1.1 The acos functions
1— acos(1) returns +0.
— acos(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for| x | > 1.

320) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ onwhen the floating-point exception is raised.
321) It is intended that undeserved ‘‘underflow’’ and ‘‘inexact’’ floating-point exceptions are raised only if
avoiding them would be too costly.

§F.9.1.1

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F.9.1.2 The asin functions
1— asin(±0) returns ±0.
— asin(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for| x | > 1.

F.9.1.3 The atan functions1— atan(±0) returns ±0.
— atan(±∞) returns ±π /2.

F.9.1.4 The atan2 functions1— atan2(±0, −0) returns ±π .322)— atan2(±0, +0) returns ±0.
— atan2(±0, x) returns ±π for x < 0.
— atan2(±0, x) returns ±0 for x > 0.
— atan2(y, ±0) returns −π /2 for y < 0.
— atan2(y, ±0) returns π /2 for y > 0.
— atan2(±y, −∞) returns ±π for finite y > 0.
— atan2(±y, +∞) returns ±0 for finite y > 0.
— atan2(±∞, x) returns ±π /2 for finite x.
— atan2(±∞, −∞) returns ±3π /4.
— atan2(±∞, +∞) returns ±π /4.

F.9.1.5 The cos functions
1— cos(±0) returns 1.
— cos(±∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.

F.9.1.6 The sin functions
1— sin(±0) returns ±0.
— sin(±∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.

322) atan2(0, 0) does not raise the ‘‘invalid’’ floating-point exception, nor does atan2( y , 0) raisethe ‘‘divide-by-zero’’ floating-point exception.

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F.9.1.7 The tan functions
1— tan(±0) returns ±0.
— tan(±∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.

F.9.2 Hyperbolic functions
F.9.2.1 The acosh functions
1— acosh(1) returns +0.
— acosh(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 1.
— acosh(+∞) returns +∞.

F.9.2.2 The asinh functions
1— asinh(±0) returns ±0.
— asinh(±∞) returns ±∞.

F.9.2.3 The atanh functions1— atanh(±0) returns ±0.
— atanh(±1) returns ±∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— atanh(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for| x | > 1.

F.9.2.4 The cosh functions
1— cosh(±0) returns 1.
— cosh(±∞) returns +∞.

F.9.2.5 The sinh functions
1— sinh(±0) returns ±0.
— sinh(±∞) returns ±∞.

F.9.2.6 The tanh functions
1— tanh(±0) returns ±0.
— tanh(±∞) returns ±1.

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F.9.3 Exponential and logarithmic functions
F.9.3.1 The exp functions
1— exp(±0) returns 1.
— exp(−∞) returns +0.
— exp(+∞) returns +∞.

F.9.3.2 The exp2 functions
1— exp2(±0) returns 1.
— exp2(−∞) returns +0.
— exp2(+∞) returns +∞.

F.9.3.3 The expm1 functions
1— expm1(±0) returns ±0.
— expm1(−∞) returns −1.
— expm1(+∞) returns +∞.

F.9.3.4 The frexp functions
1— frexp(±0, exp) returns ±0, and stores 0 in the object pointed to by exp.
— frexp(±∞, exp) returns ±∞, and stores an unspecified value in the object
pointed to by exp.
— frexp(NaN, exp) stores an unspecified value in the object pointed to by exp(and returns a NaN).

2

frexp raises no floating-point exceptions.

3

On a binary system, the body of the frexp function might be{*exp = (value == 0) ? 0 : (int)(1 + logb(value));return scalbn(value, -(*exp));}

F.9.3.5 The ilogb functions
1

If the correct result is outside the range of the return type, the numeric result is
unspecified and the ‘‘invalid’’ floating-point exception is raised.

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F.9.3.6 The ldexp functions
1

On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).

F.9.3.7 The log functions
1— log(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— log(1) returns +0.
— log(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 0.
— log(+∞) returns +∞.

F.9.3.8 The log10 functions
1— log10(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— log10(1) returns +0.
— log10(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 0.
— log10(+∞) returns +∞.

F.9.3.9 The log1p functions
1— log1p(±0) returns ±0.
— log1p(−1) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— log1p(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception forx < −1.
— log1p(+∞) returns +∞.

F.9.3.10 The log2 functions
1— log2(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— log2(1) returns +0.
— log2(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 0.
— log2(+∞) returns +∞.

F.9.3.11 The logb functions
1— logb(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— logb(±∞) returns +∞.

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F.9.3.12 The modf functions
1— modf(±x, iptr) returns a result with the same sign as x.
— modf(±∞, iptr) returns ±0 and stores ±∞ in the object pointed to by iptr.
— modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a
NaN).

2

modf behaves as though implemented by#include <math.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
double modf(double value, double *iptr){
int save_round = fegetround();fesetround(FE_TOWARDZERO);*iptr = nearbyint(value);
fesetround(save_round);return copysign(
isinf(value) ? 0.0 :value - (*iptr), value);}

F.9.3.13 The scalbn and scalbln functions1— scalbn(±0, n) returns ±0.
— scalbn(x, 0) returns x.
— scalbn(±∞, n) returns ±∞.

F.9.4 Power and absolute value functions
F.9.4.1 The cbrt functions
1— cbrt(±0) returns ±0.
— cbrt(±∞) returns ±∞.

F.9.4.2 The fabs functions
1— fabs(±0) returns +0.
— fabs(±∞) returns +∞.

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F.9.4.3 The hypot functions1— hypot(x, y), hypot(y, x), and hypot(x, −y) are equivalent.
— hypot(x, ±0) is equivalent to fabs(x).
— hypot(±∞, y) returns +∞, even if y is a NaN.

F.9.4.4 The pow functions
1— pow(±0, y) returns ±∞ and raises the ‘‘divide-by-zero’’ floating-point exception
for y an odd integer < 0.
— pow(±0, y) returns +∞ and raises the ‘‘divide-by-zero’’ floating-point exception
for y < 0 and not an odd integer.
— pow(±0, y) returns ±0 for y an odd integer > 0.
— pow(±0, y) returns +0 for y > 0 and not an odd integer.
— pow(−1, ±∞) returns 1.
— pow(+1, y) returns 1 for any y, even a NaN.
— pow(x, ±0) returns 1 for any x, even a NaN.
— pow(x, y) returns a NaN and raises the ‘‘invalid’’ floating-point exception for
finite x < 0 and finite non-integer y.
— pow(x, −∞) returns +∞ for | x | < 1.
— pow(x, −∞) returns +0 for | x | > 1.
— pow(x, +∞) returns +0 for | x | < 1.
— pow(x, +∞) returns +∞ for | x | > 1.
— pow(−∞, y) returns −0 for y an odd integer < 0.
— pow(−∞, y) returns +0 for y < 0 and not an odd integer.
— pow(−∞, y) returns −∞ for y an odd integer > 0.
— pow(−∞, y) returns +∞ for y > 0 and not an odd integer.
— pow(+∞, y) returns +0 for y < 0.
— pow(+∞, y) returns +∞ for y > 0.

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F.9.4.5 The sqrt functions
1

sqrt is fully specified as a basic arithmetic operation in IEC 60559.

F.9.5 Error and gamma functions
F.9.5.1 The erf functions
1— erf(±0) returns ±0.
— erf(±∞) returns ±1.

F.9.5.2 The erfc functions
1— erfc(−∞) returns 2.
— erfc(+∞) returns +0.

F.9.5.3 The lgamma functions
1— lgamma(1) returns +0.
— lgamma(2) returns +0.
— lgamma(x) returns +∞ and raises the ‘‘divide-by-zero’’ floating-point exception forx a negative integer or zero.
— lgamma(−∞) returns +∞.
— lgamma(+∞) returns +∞.

F.9.5.4 The tgamma functions
1— tgamma(±0) returns ±∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
— tgamma(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x anegative integer.
— tgamma(−∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.
— tgamma(+∞) returns +∞.

F.9.6 Nearest integer functions
F.9.6.1 The ceil functions
1— ceil(±0) returns ±0.
— ceil(±∞) returns ±∞.

2

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ISO/IEC 9899:TC3#include <math.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
double ceil(double x){
double result;int save_round = fegetround();fesetround(FE_UPWARD);
result = rint(x); // or nearbyint instead of rint
fesetround(save_round);return result;}

F.9.6.2 The floor functions
1— floor(±0) returns ±0.
— floor(±∞) returns ±∞.

2

See the sample implementation for ceil in F.9.6.1.

F.9.6.3 The nearbyint functions
1

The nearbyint functions use IEC 60559 rounding according to the current rounding
direction. They do not raise the ‘‘inexact’’ floating-point exception if the result differs invalue from the argument.
— nearbyint(±0) returns ±0 (for all rounding directions).
— nearbyint(±∞) returns ±∞ (for all rounding directions).

F.9.6.4 The rint functions
1

The rint functions differ from the nearbyint functions only in that they do raise the‘‘inexact’’ floating-point exception if the result differs in value from the argument.

F.9.6.5 The lrint and llrint functions
1

The lrint and llrint functions provide floating-to-integer conversion as prescribedby IEC 60559. They round according to the current rounding direction. If the roundedvalue is outside the range of the return type, the numeric result is unspecified and the‘‘invalid’’ floating-point exception is raised. When they raise no other floating-point
exception and the result differs from the argument, they raise the ‘‘inexact’’ floating-point
exception.

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F.9.6.6 The round functions
1— round(±0) returns ±0.
— round(±∞) returns ±∞.

2

The double version of round behaves as though implemented by#include <math.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
double round(double x){
double result;fenv_t save_env;
feholdexcept(&save_env);
result = rint(x);if (fetestexcept(FE_INEXACT)) {fesetround(FE_TOWARDZERO);
result = rint(copysign(0.5 + fabs(x), x));}feupdateenv(&save_env);
return result;}
The round functions may, but are not required to, raise the ‘‘inexact’’ floating-point
exception for non-integer numeric arguments, as this implementation does.

F.9.6.7 The lround and llround functions
1

The lround and llround functions differ from the lrint and llrint functions
with the default rounding direction just in that the lround and llround functions
round halfway cases away from zero and need not raise the ‘‘inexact’’ floating-point
exception for non-integer arguments that round to within the range of the return type.

F.9.6.8 The trunc functions
1

The trunc functions use IEC 60559 rounding toward zero (regardless of the current
rounding direction).
— trunc(±0) returns ±0.
— trunc(±∞) returns ±∞.

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F.9.7 Remainder functions
F.9.7.1 The fmod functions
1— fmod(±0, y) returns ±0 for y not zero.
— fmod(x, y) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x
infinite or y zero.
— fmod(x, ±∞) returns x for x not infinite.

2

The double version of fmod behaves as though implemented by#include <math.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
double fmod(double x, double y){double result;result = remainder(fabs(x), (y = fabs(y)));if (signbit(result)) result += y;return copysign(result, x);}

F.9.7.2 The remainder functions
1

The remainder functions are fully specified as a basic arithmetic operation in
IEC 60559.

F.9.7.3 The remquo functions
1

The remquo functions follow the specifications for the remainder functions. They
have no further specifications special to IEC 60559 implementations.

F.9.8 Manipulation functions
F.9.8.1 The copysign functions
1

copysign is specified in the Appendix to IEC 60559.

F.9.8.2 The nan functions
1

All IEC 60559 implementations support quiet NaNs, in all floating formats.

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F.9.8.3 The nextafter functions
1— nextafter(x, y) raises the ‘‘overflow’’ and ‘‘inexact’’ floating-point exceptions
for x finite and the function value infinite.
— nextafter(x, y) raises the ‘‘underflow’’ and ‘‘inexact’’ floating-point
exceptions for the function value subnormal or zero and x ≠ y.

F.9.8.4 The nexttoward functions
1

No additional requirements beyond those on nextafter.

F.9.9 Maximum, minimum, and positive difference functions
F.9.9.1 The fdim functions
1

No additional requirements.

F.9.9.2 The fmax functions
1

If just one argument is a NaN, the fmax functions return the other argument (if botharguments are NaNs, the functions return a NaN).

2

The body of the fmax function might be323){ return (isgreaterequal(x, y) ||isnan(y)) ? x : y; }F.9.9.3 The fmin functions
1

The fmin functions are analogous to the fmax functions (see F.9.9.2).

F.9.10 Floating multiply-add
F.9.10.1 The fma functions
1— fma(x, y, z) computes xy + z, correctly rounded once.
— fma(x, y, z) returns a NaN and optionally raises the ‘‘invalid’’ floating-point
exception if one of x and y is infinite, the other is zero, and z is a NaN.
— fma(x, y, z) returns a NaN and raises the ‘‘invalid’’ floating-point exception if
one of x and y is infinite, the other is zero, and z is not a NaN.
— fma(x, y, z) returns a NaN and raises the ‘‘invalid’’ floating-point exception if xtimes y is an exact infinity and z is also an infinity but with the opposite sign.

323) Ideally, fmax would be sensitive to the sign of zero, for example fmax(−0. 0,
return +0; however, implementation in software might be impractical.

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Annex G
(informative)
IEC 60559-compatible complex arithmetic
G.1 Introduction
1

This annex supplements annex F to specify complex arithmetic for compatibility withIEC 60559 real floating-point arithmetic. Although these specifications have been
carefully designed, there is little existing practice to validate the design decisions.
Therefore, these specifications are not normative, but should be viewed more asrecommended
practice.
An
implementation
thatdefines_ _STDC_IEC_559_COMPLEX_ _ should conform to the specifications in this annex.

G.2 Types
1

There is a new keyword _Imaginary, which is used to specify imaginary types. It is
used as a type specifier within declaration specifiers in the same way as _Complex is(thus, _Imaginary float is a valid type name).

2

There are three imaginary types, designated as float _Imaginary, double_Imaginary, and long double _Imaginary. The imaginary types (along withthe real floating and complex types) are floating types.

3

For imaginary types, the corresponding real type is given by deleting the keyword_Imaginary from the type name.

4

Each imaginary type has the same representation and alignment requirements as thecorresponding real type. The value of an object of imaginary type is the value of the real
representation times the imaginary unit.

5

The imaginary type domain comprises the imaginary types.

G.3 Conventions
1

A complex or imaginary value with at least one infinite part is regarded as an infinity(even if its other part is a NaN). A complex or imaginary value is a finite number if eachof its parts is a finite number (neither infinite nor NaN). A complex or imaginary value isa zero if each of its parts is a zero.

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G.4 Conversions
G.4.1 Imaginary types
1

Conversions among imaginary types follow rules analogous to those for real floating
types.

G.4.2 Real and imaginary
1

When a value of imaginary type is converted to a real type other than _Bool,324) the
result is a positive zero.

2

When a value of real type is converted to an imaginary type, the result is a positive
imaginary zero.

G.4.3 Imaginary and complex
1

When a value of imaginary type is converted to a complex type, the real part of thecomplex result value is a positive zero and the imaginary part of the complex result value
is determined by the conversion rules for the corresponding real types.

2

When a value of complex type is converted to an imaginary type, the real part of thecomplex value is discarded and the value of the imaginary part is converted according to
the conversion rules for the corresponding real types.

G.5 Binary operators
1

The following subclauses supplement 6.5 in order to specify the type of the result for an
operation with an imaginary operand.

2

For most operand types, the value of the result of a binary operator with an imaginary orcomplex operand is completely determined, with reference to real arithmetic, by the usualmathematical formula. For some operand types, the usual mathematical formula isproblematic because of its treatment of infinities and because of undue overflow orunderflow; in these cases the result satisfies certain properties (specified in G.5.1), but is
not completely determined.

324) See 6.3.1.2.

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G.5.1 Multiplicative operators
Semantics
1

If one operand has real type and the other operand has imaginary type, then the result has
imaginary type. If both operands have imaginary type, then the result has real type. (Ifeither operand has complex type, then the result has complex type.)2

If the operands are not both complex, then the result and floating-point exception
behavior of the * operator is defined by the usual mathematical formula:
*

u

iv

u + iv

x

xu

i(xv)

(xu) + i(xv)

iy

i(yu)

−yv

(−yv) + i(yu)(xu) + i(yu)(−yv) + i(xv)x + iy3

If the second operand is not complex, then the result and floating-point exception
behavior of the / operator is defined by the usual mathematical formula:
/

u

iv

x

x/u

i(−x/v)iy

i(y/u)y/v(x/u) + i(y/u)(y/v) + i(−x/v)

x + iy4

The * and / operators satisfy the following infinity properties for all real, imaginary, andcomplex operands:325)— if one operand is an infinity and the other operand is a nonzero finite number or an
infinity, then the result of the * operator is an infinity;— if the first operand is an infinity and the second operand is a finite number, then the
result of the / operator is an infinity;— if the first operand is a finite number and the second operand is an infinity, then the
result of the / operator is a zero;325) These properties are already implied for those cases covered in the tables, but are required for all cases(at least where the state for CX_LIMITED_RANGE is ‘‘off’’).

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5

If both operands of the * operator are complex or if the second operand of the / operator
is complex, the operator raises floating-point exceptions if appropriate for the calculationof the parts of the result, and may raise spurious floating-point exceptions.

6

EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Notethat the imaginary unit I has imaginary type (see G.6).
#include <math.h>#include <complex.h>/* Multiply z * w ... */double complex _Cmultd(double complex z, double complex w){#pragma STDC FP_CONTRACT OFF
double a, b, c, d, ac, bd, ad, bc, x, y;a = creal(z); b = cimag(z);c = creal(w); d = cimag(w);ac = a * c;bd = b * d;ad = a * d;bc = b * c;x = ac - bd; y = ad + bc;
if (isnan(x) && isnan(y)) {/* Recover infinities that computed as NaN+iNaN ... */int recalc = 0;
if ( isinf(a) || isinf(b) ) { // z is infinite/* "Box" the infinity and change NaNs in the other factor to 0 */a = copysign(isinf(a) ? 1.0 : 0.0, a);b = copysign(isinf(b) ? 1.0 : 0.0, b);if (isnan(c)) c = copysign(0.0, c);if (isnan(d)) d = copysign(0.0, d);recalc = 1;}
if ( isinf(c) || isinf(d) ) { // w is infinite/* "Box" the infinity and change NaNs in the other factor to 0 */c = copysign(isinf(c) ? 1.0 : 0.0, c);
d = copysign(isinf(d) ? 1.0 : 0.0, d);if (isnan(a)) a = copysign(0.0, a);if (isnan(b)) b = copysign(0.0, b);
recalc = 1;}
if (!recalc && (isinf(ac) || isinf(bd) ||isinf(ad) || isinf(bc))) {/* Recover infinities from overflow by changing NaNs to 0 ... */if (isnan(a)) a = copysign(0.0, a);if (isnan(b)) b = copysign(0.0, b);if (isnan(c)) c = copysign(0.0, c);if (isnan(d)) d = copysign(0.0, d);recalc = 1;}
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x = INFINITY * ( a * c - b * d );y = INFINITY * ( a * d + b * c );}}return x + I * y;}7This implementation achieves the required treatment of infinities at the cost of only one isnan test in
ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur.

8

EXAMPLE 2

Division of two double _Complex operands could be implemented as follows.

#include <math.h>#include <complex.h>/* Divide z / w ... */double complex _Cdivd(double complex z, double complex w){#pragma STDC FP_CONTRACT OFF
double a, b, c, d, logbw, denom, x, y;
int ilogbw = 0;a = creal(z); b = cimag(z);c = creal(w); d = cimag(w);logbw = logb(fmax(fabs(c), fabs(d)));if (isfinite(logbw)) {ilogbw = (int)logbw;
c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw);}
denom = c * c + d * d;x = scalbn((a * c + b * d) / denom, -ilogbw);
y = scalbn((b * c - a * d) / denom, -ilogbw);/* Recover infinities and zeros that computed as NaN+iNaN;*//* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */if (isnan(x) && isnan(y)) {if ((denom == 0.0) &&(!isnan(a) || !isnan(b))) {x = copysign(INFINITY, c) * a;y = copysign(INFINITY, c) * b;}else if ((isinf(a) || isinf(b)) &&isfinite(c) && isfinite(d)) {a = copysign(isinf(a) ? 1.0 : 0.0, a);b = copysign(isinf(b) ? 1.0 : 0.0, b);
x = INFINITY * ( a * c + b * d );y = INFINITY * ( b * c - a * d );}else if (isinf(logbw) &&isfinite(a) && isfinite(b)) {c = copysign(isinf(c) ? 1.0 : 0.0, c);
d = copysign(isinf(d) ? 1.0 : 0.0, d);x = 0.0 * ( a * c + b * d );y = 0.0 * ( b * c - a * d );§G.5.1

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return x + I * y;}

9

Scaling the denominator alleviates the main overflow and underflow problem, which is more serious thanfor multiplication. In the spirit of the multiplication example above, this code does not defend against
overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead ofwith division, provides better roundoff characteristics.

G.5.2 Additive operators
Semantics
1

If both operands have imaginary type, then the result has imaginary type. (If one operand
has real type and the other operand has imaginary type, or if either operand has complex
type, then the result has complex type.)2

In all cases the result and floating-point exception behavior of a + or - operator is definedby the usual mathematical formula:uiv

u + ivxx±u

x ± iv(x ± u) ± iv

iy

±u + iyi(y ± v)

±u + i(y ± v)

(x ± u) + iy

x + i(y ± v)

(x ± u) + i(y ± v)

+ or −

x + iyG.6 Complex arithmetic <complex.h>1

The macros
imaginaryand_Imaginary_I
are defined, respectively, as _Imaginary and a constant expression of type const
float _Imaginary with the value of the imaginary unit. The macroI
is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding
the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro
imaginary.

2This subclause contains specifications for the <complex.h> functions that are
particularly suited to IEC 60559 implementations. For families of functions, thespecifications apply to all of the functions even though only the principal function is472

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shown. Unless otherwise specified, where the symbol ‘‘±’’ occurs in both an argument
and the result, the result has the same sign as the argument.
3

The functions are continuous onto both sides of their branch cuts, taking into account thesign of zero. For example, csqrt(−2 ± i0) = ±i√ 2.

4

Since complex and imaginary values are composed of real values, each function may be
regarded as computing real values from real values. Except as noted, the functions treat
real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in amanner consistent with the specifications for real functions in F.9.326)

5

The functions cimag, conj, cproj, and creal are fully specified for all
implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floatingpoint exceptions.

6

Each of the functions cabs and carg is specified by a formula in terms of a realfunction (whose special cases are covered in annex F):
cabs(x + iy) = hypot(x, y)carg(x + iy) = atan2(y, x)

7Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by
a formula in terms of other complex functions (whose special cases are specified below):
casin(z) = −i casinh(iz)catan(z) = −i catanh(iz)ccos(z) = ccosh(iz)csin(z) = −i csinh(iz)ctan(z) = −i ctanh(iz)8For the other functions, the following subclauses specify behavior for special cases,
including treatment of the ‘‘invalid’’ and ‘‘divide-by-zero’’ floating-point exceptions. For
families of functions, the specifications apply to all of the functions even though only theprincipal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), thespecifications for the upper half-plane imply the specifications for the lower half-plane; if
the function f is also either even, f (−z) = f (z), or odd, f (−z) = − f (z), then thespecifications for the first quadrant imply the specifications for the other three quadrants.

9

In the following subclauses, cis(y) is defined as cos(y) + i sin(y).

326) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its
other part is a NaN.

§G.6

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G.6.1 Trigonometric functions
G.6.1.1 The cacos functions
1— cacos(conj(z)) = conj(cacos(z)).
— cacos(±0 + i0) returns π /2 − i0.
— cacos(±0 + iNaN) returns π /2 + iNaN.
— cacos(x + i ∞) returns π /2 − i ∞, for finite x.
— cacos(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for nonzero finite x.
— cacos(−∞ + iy) returns π − i ∞, for positive-signed finite y.
— cacos(+∞ + iy) returns +0 − i ∞, for positive-signed finite y.
— cacos(−∞ + i ∞) returns 3π /4 − i ∞.
— cacos(+∞ + i ∞) returns π /4 − i ∞.
— cacos(±∞ + iNaN) returns NaN ± i ∞ (where the sign of the imaginary part of theresult is unspecified).
— cacos(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite y.
— cacos(NaN + i ∞) returns NaN − i ∞.
— cacos(NaN + iNaN) returns NaN + iNaN.

G.6.2 Hyperbolic functions
G.6.2.1 The cacosh functions
1— cacosh(conj(z)) = conj(cacosh(z)).
— cacosh(±0 + i0) returns +0 + iπ /2.
— cacosh(x + i ∞) returns +∞ + iπ /2, for finite x.
— cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’
floating-point exception, for finite x.
— cacosh(−∞ + iy) returns +∞ + iπ , for positive-signed finite y.
— cacosh(+∞ + iy) returns +∞ + i0, for positive-signed finite y.
— cacosh(−∞ + i ∞) returns +∞ + i3π /4.
— cacosh(+∞ + i ∞) returns +∞ + iπ /4.
— cacosh(±∞ + iNaN) returns +∞ + iNaN.
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ISO/IEC 9899:TC3— cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’
floating-point exception, for finite y.
— cacosh(NaN + i ∞) returns +∞ + iNaN.
— cacosh(NaN + iNaN) returns NaN + iNaN.

G.6.2.2 The casinh functions
1— casinh(conj(z)) = conj(casinh(z)) and casinh is odd.
— casinh(+0 + i0) returns 0 + i0.
— casinh(x + i ∞) returns +∞ + iπ /2 for positive-signed finite x.
— casinh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’
floating-point exception, for finite x.
— casinh(+∞ + iy) returns +∞ + i0 for positive-signed finite y.
— casinh(+∞ + i ∞) returns +∞ + iπ /4.
— casinh(+∞ + iNaN) returns +∞ + iNaN.
— casinh(NaN + i0) returns NaN + i0.
— casinh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’
floating-point exception, for finite nonzero y.
— casinh(NaN + i ∞) returns ±∞ + iNaN (where the sign of the real part of the result
is unspecified).
— casinh(NaN + iNaN) returns NaN + iNaN.

G.6.2.3 The catanh functions
1— catanh(conj(z)) = conj(catanh(z)) and catanh is odd.
— catanh(+0 + i0) returns +0 + i0.
— catanh(+0 + iNaN) returns +0 + iNaN.
— catanh(+1 + i0) returns +∞ + i0 and raises the ‘‘divide-by-zero’’ floating-point
exception.
— catanh(x + i ∞) returns +0 + iπ /2, for finite positive-signed x.
— catanh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’
floating-point exception, for nonzero finite x.
— catanh(+∞ + iy) returns +0 + iπ /2, for finite positive-signed y.
— catanh(+∞ + i ∞) returns +0 + iπ /2.
— catanh(+∞ + iNaN) returns +0 + iNaN.
§G.6.2.3

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floating-point exception, for finite y.
— catanh(NaN + i ∞) returns ±0 + iπ /2 (where the sign of the real part of the result is
unspecified).
— catanh(NaN + iNaN) returns NaN + iNaN.

G.6.2.4 The ccosh functions
1— ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even.
— ccosh(+0 + i0) returns 1 + i0.
— ccosh(+0 + i ∞) returns NaN ± i0 (where the sign of the imaginary part of theresult is unspecified) and raises the ‘‘invalid’’ floating-point exception.
— ccosh(+0 + iNaN) returns NaN ± i0 (where the sign of the imaginary part of theresult is unspecified).
— ccosh(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
exception, for finite nonzero x.
— ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite nonzero x.
— ccosh(+∞ + i0) returns +∞ + i0.
— ccosh(+∞ + iy) returns +∞ cis(y), for finite nonzero y.
— ccosh(+∞ + i ∞) returns ±∞ + iNaN (where the sign of the real part of the result is
unspecified) and raises the ‘‘invalid’’ floating-point exception.
— ccosh(+∞ + iNaN) returns +∞ + iNaN.
— ccosh(NaN + i0) returns NaN ± i0 (where the sign of the imaginary part of theresult is unspecified).
— ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for all nonzero numbers y.
— ccosh(NaN + iNaN) returns NaN + iNaN.

G.6.2.5 The csinh functions
1— csinh(conj(z)) = conj(csinh(z)) and csinh is odd.
— csinh(+0 + i0) returns +0 + i0.
— csinh(+0 + i ∞) returns ±0 + iNaN (where the sign of the real part of the result is
unspecified) and raises the ‘‘invalid’’ floating-point exception.
— csinh(+0 + iNaN) returns ±0 + iNaN (where the sign of the real part of the result is
unspecified).
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ISO/IEC 9899:TC3— csinh(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
exception, for positive finite x.
— csinh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite nonzero x.
— csinh(+∞ + i0) returns +∞ + i0.
— csinh(+∞ + iy) returns +∞ cis(y), for positive finite y.
— csinh(+∞ + i ∞) returns ±∞ + iNaN (where the sign of the real part of the result is
unspecified) and raises the ‘‘invalid’’ floating-point exception.
— csinh(+∞ + iNaN) returns ±∞ + iNaN (where the sign of the real part of the result
is unspecified).
— csinh(NaN + i0) returns NaN + i0.
— csinh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for all nonzero numbers y.
— csinh(NaN + iNaN) returns NaN + iNaN.

G.6.2.6 The ctanh functions
1— ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd.
— ctanh(+0 + i0) returns +0 + i0.
— ctanh(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
exception, for finite x.
— ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite x.
— ctanh(+∞ + iy) returns 1 + i0 sin(2y), for positive-signed finite y.
— ctanh(+∞ + i ∞) returns 1 ± i0 (where the sign of the imaginary part of the result
is unspecified).
— ctanh(+∞ + iNaN) returns 1 ± i0 (where the sign of the imaginary part of theresult is unspecified).
— ctanh(NaN + i0) returns NaN + i0.
— ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for all nonzero numbers y.
— ctanh(NaN + iNaN) returns NaN + iNaN.

§G.6.2.6

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G.6.3 Exponential and logarithmic functions
G.6.3.1 The cexp functions
1— cexp(conj(z)) = conj(cexp(z)).
— cexp(±0 + i0) returns 1 + i0.
— cexp(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
exception, for finite x.
— cexp(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite x.
— cexp(+∞ + i0) returns +∞ + i0.
— cexp(−∞ + iy) returns +0 cis(y), for finite y.
— cexp(+∞ + iy) returns +∞ cis(y), for finite nonzero y.
— cexp(−∞ + i ∞) returns ±0 ± i0 (where the signs of the real and imaginary parts of
the result are unspecified).
— cexp(+∞ + i ∞) returns ±∞ + iNaN and raises the ‘‘invalid’’ floating-point
exception (where the sign of the real part of the result is unspecified).
— cexp(−∞ + iNaN) returns ±0 ± i0 (where the signs of the real and imaginary partsof the result are unspecified).
— cexp(+∞ + iNaN) returns ±∞ + iNaN (where the sign of the real part of the result
is unspecified).
— cexp(NaN + i0) returns NaN + i0.
— cexp(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for all nonzero numbers y.

— cexp(NaN + iNaN) returns NaN + iNaN.

G.6.3.2 The clog functions
1— clog(conj(z)) = conj(clog(z)).
— clog(−0 + i0) returns −∞ + iπ and raises the ‘‘divide-by-zero’’ floating-point
exception.
— clog(+0 + i0) returns −∞ + i0 and raises the ‘‘divide-by-zero’’ floating-point
exception.
— clog(x + i ∞) returns +∞ + iπ /2, for finite x.
— clog(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite x.
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ISO/IEC 9899:TC3— clog(−∞ + iy) returns +∞ + iπ , for finite positive-signed y.
— clog(+∞ + iy) returns +∞ + i0, for finite positive-signed y.
— clog(−∞ + i ∞) returns +∞ + i3π /4.
— clog(+∞ + i ∞) returns +∞ + iπ /4.
— clog(±∞ + iNaN) returns +∞ + iNaN.
— clog(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite y.
— clog(NaN + i ∞) returns +∞ + iNaN.
— clog(NaN + iNaN) returns NaN + iNaN.

G.6.4 Power and absolute-value functions
G.6.4.1 The cpow functions
1

The cpow functions raise floating-point exceptions if appropriate for the calculation of
the parts of the result, and may raise spurious exceptions.327)

G.6.4.2 The csqrt functions
1— csqrt(conj(z)) = conj(csqrt(z)).
— csqrt(±0 + i0) returns +0 + i0.
— csqrt(x + i ∞) returns +∞ + i ∞, for all x (including NaN).
— csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite x.
— csqrt(−∞ + iy) returns +0 + i ∞, for finite positive-signed y.
— csqrt(+∞ + iy) returns +∞ + i0, for finite positive-signed y.
— csqrt(−∞ + iNaN) returns NaN ± i ∞ (where the sign of the imaginary part of theresult is unspecified).
— csqrt(+∞ + iNaN) returns +∞ + iNaN.
— csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floatingpoint exception, for finite y.
— csqrt(NaN + iNaN) returns NaN + iNaN.

327) This allows cpow( z , c ) to be implemented as cexp(cimplementations that treat special cases more carefully.

§G.6.4.2

clog( z )) without precluding

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G.7 Type-generic math <tgmath.h>1Type-generic macros that accept complex arguments also accept imaginary arguments. If
an argument is imaginary, the macro expands to an expression whose type is real,
imaginary, or complex, as appropriate for the particular function: if the argument isimaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; thetypes of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; andthe types of the others are complex.

2

Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh,sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of realfunctions:cos(iy)= cosh(y)sin(iy)= i sinh(y)tan(iy)= i tanh(y)cosh(iy) = cos(y)sinh(iy) = i sin(y)tanh(iy) = i tan(y)asin(iy) = i asinh(y)atan(iy) = i atanh(y)asinh(iy) = i asin(y)atanh(iy) = i atan(y)480

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Annex H(informative)
Language independent arithmetic
H.1 Introduction
1

This annex documents the extent to which the C language supports the ISO/IEC 10967−1
standard for language-independent arithmetic (LIA−1). LIA−1 is more general thanIEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics.

H.2 Types
1

The relevant C arithmetic types meet the requirements of LIA−1 types if an
implementation adds notification of exceptional arithmetic operations and meets the 1
unit in the last place (ULP) accuracy requirement (LIA−1 subclause 5.2.8).

H.2.1 Boolean type1

The LIA−1 data type Boolean is implemented by the C data type bool with values oftrue and false, all from <stdbool.h>.

H.2.2 Integer types
1

The signed C integer types int, long int, long long int, and the corresponding
unsigned types are compatible with LIA−1. If an implementation adds support for the
LIA−1 exceptional values ‘‘integer_overflow’’ and ‘‘undefined’’, then those types are
LIA−1 conformant types. C’s unsigned integer types are ‘‘modulo’’ in the LIA−1 sensein that overflows or out-of-bounds results silently wrap. An implementation that defines
signed integer types as also being modulo need not detect integer overflow, in which case,only integer divide-by-zero need be detected.

2

The parameters for the integer data types can be accessed by the following:3

maxint

INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX,ULLONG_MAX

minint

INT_MIN, LONG_MIN, LLONG_MIN

The parameter ‘‘bounded’’ is always true, and is not provided. The parameter ‘‘minint’’is always 0 for the unsigned types, and is not provided for those types.

§H.2.2

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H.2.2.1 Integer operations
1

The integer operations on integer types are the following:
addI

x + y

subI

x - y

mulI

x * y

divI, divtI

x / y

remI, remtI

x % y

negI

-x

absI

abs(x), labs(x), llabs(x)eqI

x == yneqI

x != y

lssI

x < y

leqI

x <= y

gtrI

x > y

geqI

x >= ywhere x and y are expressions of the same integer type.

H.2.3 Floating-point types
1

The C floating-point types float, double, and long double are compatible with
LIA−1. If an implementation adds support for the LIA−1 exceptional values‘‘underflow’’, ‘‘floating_overflow’’, and ‘‘"undefined’’, then those types are conformant
with LIA−1. An implementation that uses IEC 60559 floating-point formats andoperations (see annex F) along with IEC 60559 status flags and traps has LIA−1
conformant types.

H.2.3.1 Floating-point parameters
1

2

The parameters for a floating point data type can be accessed by the following:r

FLT_RADIXp

FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG

emax

FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP

emin

FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP

The derived constants for the floating point types are accessed by the following:

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fmax

FLT_MAX, DBL_MAX, LDBL_MAX

fminN

FLT_MIN, DBL_MIN, LDBL_MIN

epsilon

FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON

rnd_style

FLT_ROUNDS

ISO/IEC 9899:TC3

H.2.3.2 Floating-point operations
1

The floating-point operations on floating-point types are the following:
addF

x + y

subF

x - y

mulF

x * y

divF

x / y

negF

-x

absF

fabsf(x), fabs(x), fabsl(x)exponentF

1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)scaleFscalbnf(x, n), scalbn(x, n), scalbnl(x, n),scalblnf(x, li), scalbln(x, li), scalblnl(x, li)

intpartF

modff(x, &y), modf(x, &y), modfl(x, &y)

fractpartF

modff(x, &y), modf(x, &y), modfl(x, &y)eqF

x == yneqF

x != y

lssF

x < y

leqF

x <= y

gtrF

x > y

geqF

x >= ywhere x and y are expressions of the same floating point type, n is of type int, and li
is of type long int.

H.2.3.3 Rounding styles
1

The C Standard requires all floating types to use the same radix and rounding style, sothat only one identifier for each is provided to map to LIA−1.

2

The FLT_ROUNDS parameter can be used to indicate the LIA−1 rounding styles:
truncate§H.2.3.3

FLT_ROUNDS == 0
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nearest

FLT_ROUNDS == 1

other

FLT_ROUNDS != 0 && FLT_ROUNDS != 1

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provided that an implementation extends FLT_ROUNDS to cover the rounding style usedin all relevant LIA−1 operations, not just addition as in C.

H.2.4 Type conversions
1

The LIA−1 type conversions are the following type casts:
cvtI’ → I(int)i, (long int)i, (long long int)i,(unsigned int)i, (unsigned long int)i,(unsigned long long int)i

cvtF → I(int)x, (long int)x, (long long int)x,(unsigned int)x, (unsigned long int)x,(unsigned long long int)x

cvtI → F(float)i, (double)i, (long double)i

cvtF’ → F

(float)x, (double)x, (long double)x2

In the above conversions from floating to integer, the use of (cast)x can be replaced with(cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),(cast)ceil(x), or (cast)floor(x). In addition, C’s floating-point to integer
conversion functions, lrint(), llrint(), lround(), and llround(), can beused. They all meet LIA−1’s requirements on floating to integer rounding for in-range
values. For out-of-range values, the conversions shall silently wrap for the modulo types.

3

The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g.,fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x),65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0
to 65535.0 which can then be cast to unsigned short int. But, theremainder() function is not useful for doing silent wrapping to signed integer types,
e.g., remainder( rint(x), 65536.0 ) will compute an integer value in therange −32767.0 to +32768.0 which is not, in general, in the range of signed shortint.

4

C’s conversions (casts) from floating-point to floating-point can meet LIA−1
requirements if an implementation uses round-to-nearest (IEC 60559 default).

5

C’s conversions (casts) from integer to floating-point can meet LIA−1 requirements if an
implementation uses round-to-nearest.

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H.3 Notification1

Notification is the process by which a user or program is informed that an exceptionalarithmetic operation has occurred. C’s operations are compatible with LIA−1 in that C
allows an implementation to cause a notification to occur when any arithmetic operation
returns an exceptional value as defined in LIA−1 clause 5.

H.3.1 Notification alternatives
1

LIA−1 requires at least the following two alternatives for handling of notifications:setting indicators or trap-and-terminate. LIA−1 allows a third alternative: trap-andresume.

2

An implementation need only support a given notification alternative for the entire
program. An implementation may support the ability to switch between notification
alternatives during execution, but is not required to do so. An implementation can
provide separate selection for each kind of notification, but this is not required.

3

C allows an implementation to provide notification. C’s SIGFPE (for traps) and
FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators)
can provide LIA−1 notification.

4

C’s signal handlers are compatible with LIA−1. Default handling of SIGFPE canprovide trap-and-terminate behavior, except for those LIA−1 operations implemented bymath library function calls. User-provided signal handlers for SIGFPE allow for trapand-resume behavior with the same constraint.

H.3.1.1 Indicators
1

C’s <fenv.h> status flags are compatible with the LIA−1 indicators.

2

The following mapping is for floating-point types:

3

undefined

FE_INVALID, FE_DIVBYZERO

floating_overflow

FE_OVERFLOW

underflow

FE_UNDERFLOW

The floating-point indicator interrogation and manipulation operations are:set_indicators

feraiseexcept(i)clear_indicators

feclearexcept(i)test_indicators

fetestexcept(i)current_indicators

fetestexcept(FE_ALL_EXCEPT)

where i is an expression of type int representing a subset of the LIA−1 indicators.
4

C allows an implementation to provide the following LIA−1 required behavior: at
program termination if any indicator is set the implementation shall send an unambiguous§H.3.1.1
Language independent arithmetic
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and ‘‘hard to ignore’’ message (see LIA−1 subclause 6.1.2)
5

LIA−1 does not make the distinction between floating-point and integer for ‘‘undefined’’.
This documentation makes that distinction because <fenv.h> covers only the floatingpoint indicators.

H.3.1.2 Traps
1

C is compatible with LIA−1’s trap requirements for arithmetic operations, but not formath library functions (which are not permitted to generate any externally visible
exceptional conditions). An implementation can provide an alternative of notification
through termination with a ‘‘hard-to-ignore’’ message (see LIA−1 subclause 6.1.3).

2

LIA−1 does not require that traps be precise.

3

C does require that SIGFPE be the signal corresponding to arithmetic exceptions, if there
is any signal raised for them.

4

C supports signal handlers for SIGFPE and allows trapping of arithmetic exceptions.
When arithmetic exceptions do trap, C’s signal-handler mechanism allows trap-andterminate (either default implementation behavior or user replacement for it) or trap-andresume, at the programmer’s option.

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Annex I
(informative)
Common warnings
1

An implementation may generate warnings in many situations, none of which are
specified as part of this International Standard. The following are a few of the morecommon situations.

2— A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3).
— A block with initialization of an object that has automatic storage duration is jumped
into (6.2.4).
— An implicit narrowing conversion is encountered, such as the assignment of a long
int or a double to an int, or a pointer to void to a pointer to any type other thana character type (6.3).
— A hexadecimal floating constant cannot be represented exactly in its evaluation format(6.4.4.2).
— An integer character constant includes more than one character or a wide character
constant includes more than one multibyte character (6.4.4.4).
— The characters /* are found in a comment (6.4.7).
— An ‘‘unordered’’ binary operator (not comma, &&, or ||) contains a side effect to an
lvalue in one operand, and a side effect to, or an access to the value of, the identicallvalue in the other operand (6.5).

— A function is called but no prototype has been supplied (6.5.2.2).
— The arguments in a function call do not agree in number and type with those of theparameters in a function definition that is not a prototype (6.5.2.2).
— An object is defined but not used (6.7).
— A value is given to an object of an enumerated type other than by assignment of an
enumeration constant that is a member of that type, or an enumeration object that has
the same type, or the value of a function that returns the same enumerated type(6.7.2.2).

— An aggregate has a partly bracketed initialization (6.7.7).
— A statement cannot be reached (6.8).
— A statement with no apparent effect is encountered (6.8).
— A constant expression is used as the controlling expression of a selection statement(6.8.4).
§I

Common warnings

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WG14/N1256— An incorrectly formed preprocessing group is encountered while skipping a
preprocessing group (6.10.1).
— An unrecognized #pragma directive is encountered (6.10.6).

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Annex J
(informative)
Portability issues
1This annex collects some information about portability that appears in this International
Standard.

J.1 Unspecified behavior
1

The following are unspecified:— The manner and timing of static initialization (5.1.2).
— The termination status returned to the hosted environment if the return type of main
is not compatible with int (5.1.2.2.3).
— The behavior of the display device if a printing character is written when the active
position is at the final position of a line (5.2.2).
— The behavior of the display device if a backspace character is written when the active
position is at the initial position of a line (5.2.2).
— The behavior of the display device if a horizontal tab character is written when theactive position is at or past the last defined horizontal tabulation position (5.2.2).
— The behavior of the display device if a vertical tab character is written when the active
position is at or past the last defined vertical tabulation position (5.2.2).
— How an extended source character that does not correspond to a universal charactername counts toward the significant initial characters in an external identifier (5.2.4.1).
— Many aspects of the representations of types (6.2.6).
— The value of padding bytes when storing values in structures or unions (6.2.6.1).
— The value of a union member other than the last one stored into (6.2.6.1).
— The representation used when storing a value in an object that has more than one
object representation for that value (6.2.6.1).
— The values of any padding bits in integer representations (6.2.6.2).
— Whether certain operators can generate negative zeros and whether a negative zero
becomes a normal zero when stored in an object (6.2.6.2).
— Whether two string literals result in distinct arrays (6.4.5).
— The order in which subexpressions are evaluated and the order in which side effects
take place, except as specified for the function-call (), &&, ||, ?:, and comma
operators (6.5).
§J.1

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WG14/N1256— The order in which the function designator, arguments, and subexpressions within thearguments are evaluated in a function call (6.5.2.2).
— The order of side effects among compound literal initialization list expressions(6.5.2.5).
— The order in which the operands of an assignment operator are evaluated (6.5.16).
— The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1).
— Whether a call to an inline function uses the inline definition or the external definitionof the function (6.7.4).
— Whether or not a size expression is evaluated when it is part of the operand of asizeof operator and changing the value of the size expression would not affect theresult of the operator (6.7.5.2).
— The order in which any side effects occur among the initialization list expressions in
an initializer (6.7.8).
— The layout of storage for function parameters (6.9.1).
— When a fully expanded macro replacement list contains a function-like macro nameas its last preprocessing token and the next preprocessing token from the source file isa (, and the fully expanded replacement of that macro ends with the name of the firstmacro and the next preprocessing token from the source file is again a (, whether thatis considered a nested replacement (6.10.3).
— The order in which # and ## operations are evaluated during macro substitution(6.10.3.2, 6.10.3.3).
— Whether errno is a macro or an identifier with external linkage (7.5).
— The state of the floating-point status flags when execution passes from a part of the
program translated with FENV_ACCESS ‘‘off’’ to a part translated with
FENV_ACCESS ‘‘on’’ (7.6.1).
— The order in which feraiseexcept raises floating-point exceptions, except as
stated in F.7.6 (7.6.2.3).
— Whether math_errhandling is a macro or an identifier with external linkage(7.12).
— The results of the frexp functions when the specified value is not a floating-point
number (7.12.6.4).
— The numeric result of the ilogb functions when the correct value is outside therange of the return type (7.12.6.5, F.9.3.5).

— The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.9.6.5).
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ISO/IEC 9899:TC3— The value stored by the remquo functions in the object pointed to by quo when y iszero (7.12.10.3).

— Whether setjmp is a macro or an identifier with external linkage (7.13).
— Whether va_copy and va_end are macros or identifiers with external linkage(7.15.1).
— The hexadecimal digit before the decimal point when a non-normalized floating-point
number is printed with an a or A conversion specifier (7.19.6.1, 7.24.2.1).
— The value of the file position indicator after a successful call to the ungetc function
for a text stream, or the ungetwc function for any stream, until all pushed-backcharacters are read or discarded (7.19.7.11, 7.24.3.10).
— The details of the value stored by the fgetpos function (7.19.9.1).
— The details of the value returned by the ftell function for a text stream (7.19.9.4).
— Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstoldfunctions convert a minus-signed sequence to a negative number directly or by
negating the value resulting from converting the corresponding unsigned sequence(7.20.1.3, 7.24.4.1.1).
— The order and contiguity of storage allocated by successive calls to the calloc,
malloc, and realloc functions (7.20.3).
— The amount of storage allocated by a successful call to the calloc, malloc, orrealloc function when 0 bytes was requested (7.20.3).
— Which of two elements that compare as equal is matched by the bsearch function(7.20.5.1).
— The order of two elements that compare as equal in an array sorted by the qsort
function (7.20.5.2).
— The encoding of the calendar time returned by the time function (7.23.2.4).
— The characters stored by the strftime or wcsftime function if any of the timevalues being converted is outside the normal range (7.23.3.5, 7.24.5.1).
— The conversion state after an encoding error occurs (7.24.6.3.2, 7.24.6.3.3, 7.24.6.4.1,
7.24.6.4.2,— The resulting value when the ‘‘invalid’’ floating-point exception is raised during
IEC 60559 floating to integer conversion (F.4).
— Whether conversion of non-integer IEC 60559 floating values to integer raises the‘‘inexact’’ floating-point exception (F.4).

§J.1

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WG14/N1256— Whether or when library functions in <math.h> raise the ‘‘inexact’’ floating-point
exception in an IEC 60559 conformant implementation (F.9).

— Whether or when library functions in <math.h> raise an undeserved ‘‘underflow’’floating-point exception in an IEC 60559 conformant implementation (F.9).

— The exponent value stored by frexp for a NaN or infinity (F.9.3.4).
— The numeric result returned by the lrint, llrint, lround, and llround
functions if the rounded value is outside the range of the return type (F.9.6.5, F.9.6.7).
— The sign of one part of the complex result of several math functions for certain
exceptional values in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2,
G.6.2.3, G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2).

J.2 Undefined behavior
1

The behavior is undefined in the following circumstances:— A ‘‘shall’’ or ‘‘shall not’’ requirement that appears outside of a constraint is violated(clause 4).
— A nonempty source file does not end in a new-line character which is not immediately
preceded by a backslash character or ends in a partial preprocessing token orcomment (5.1.1.2).
— Token concatenation produces a character sequence matching the syntax of auniversal character name (5.1.1.2).
— A program in a hosted environment does not define a function named main using oneof the specified forms (5.1.2.2.1).
— A character not in the basic source character set is encountered in a source file, except
in an identifier, a character constant, a string literal, a header name, a comment, or a
preprocessing token that is never converted to a token (5.2.1).
— An identifier, comment, string literal, character constant, or header name contains aninvalid multibyte character or does not begin and end in the initial shift state (5.2.1.2).
— The same identifier has both internal and external linkage in the same translation unit
(6.2.2).
— An object is referred to outside of its lifetime (6.2.4).
— The value of a pointer to an object whose lifetime has ended is used (6.2.4).
— The value of an object with automatic storage duration is used while it isindeterminate (6.2.4, 6.7.8, 6.8).
— A trap representation is read by an lvalue expression that does not have character type(6.2.6.1).
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ISO/IEC 9899:TC3— A trap representation is produced by a side effect that modifies any part of the object
using an lvalue expression that does not have character type (6.2.6.1).
— The arguments to certain operators are such that could produce a negative zero result,but the implementation does not support negative zeros (6.2.6.2).
— Two declarations of the same object or function specify types that are not compatible(6.2.7).
— Conversion to or from an integer type produces a value outside the range that can be
represented (6.3.1.4).
— Demotion of one real floating type to another produces a value outside the range thatcan be represented (6.3.1.5).
— An lvalue does not designate an object when evaluated (6.3.2.1).
— A non-array lvalue with an incomplete type is used in a context that requires the valueof the designated object (6.3.2.1).
— An lvalue having array type is converted to a pointer to the initial element of thearray, and the array object has register storage class (6.3.2.1).
— An attempt is made to use the value of a void expression, or an implicit or explicit
conversion (except to void) is applied to a void expression (6.3.2.2).
— Conversion of a pointer to an integer type produces a value outside the range that canbe represented (6.3.2.3).
— Conversion between two pointer types produces a result that is incorrectly aligned(6.3.2.3).
— A pointer is used to call a function whose type is not compatible with the pointed-to
type (6.3.2.3).
— An unmatched ' or " character is encountered on a logical source line during
tokenization (6.4).
— A reserved keyword token is used in translation phase 7 or 8 for some purpose otherthan as a keyword (6.4.1).
— A universal character name in an identifier does not designate a character whose
encoding falls into one of the specified ranges (6.4.2.1).
— The initial character of an identifier is a universal character name designating a digit(6.4.2.1).
— Two identifiers differ only in nonsignificant characters (6.4.2.1).
— The identifier _ _func_ _ is explicitly declared (6.4.2.2).

§J.2

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WG14/N1256— The program attempts to modify a string literal (6.4.5).
— The characters ', \, ", //, or /* occur in the sequence between the < and >delimiters, or the characters ', \, //, or /* occur in the sequence between the "delimiters, in a header name preprocessing token (6.4.7).
— Between two sequence points, an object is modified more than once, or is modified
and the prior value is read other than to determine the value to be stored (6.5).
— An exceptional condition occurs during the evaluation of an expression (6.5).
— An object has its stored value accessed other than by an lvalue of an allowable type(6.5).
— An attempt is made to modify the result of a function call, a conditional operator, anassignment operator, or a comma operator, or to access it after the next sequence
point (6.5.2.2, 6.5.15, 6.5.16, 6.5.17).
— For a call to a function without a function prototype in scope, the number ofarguments does not equal the number of parameters (6.5.2.2).
— For call to a function without a function prototype in scope where the function isdefined with a function prototype, either the prototype ends with an ellipsis or thetypes of the arguments after promotion are not compatible with the types of theparameters (6.5.2.2).
— For a call to a function without a function prototype in scope where the function is notdefined with a function prototype, the types of the arguments after promotion are notcompatible with those of the parameters after promotion (with certain exceptions)(6.5.2.2).
— A function is defined with a type that is not compatible with the type (of theexpression) pointed to by the expression that denotes the called function (6.5.2.2).
— The operand of the unary * operator has an invalid value (6.5.3.2).
— A pointer is converted to other than an integer or pointer type (6.5.4).
— The value of the second operand of the / or % operator is zero (6.5.5).
— Addition or subtraction of a pointer into, or just beyond, an array object and an
integer type produces a result that does not point into, or just beyond, the same arrayobject (6.5.6).
— Addition or subtraction of a pointer into, or just beyond, an array object and an
integer type produces a result that points just beyond the array object and is used as
the operand of a unary * operator that is evaluated (6.5.6).
— Pointers that do not point into, or just beyond, the same array object are subtracted(6.5.6).
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ISO/IEC 9899:TC3— An array subscript is out of range, even if an object is apparently accessible with thegiven subscript (as in the lvalue expression a[1][7] given the declaration int
a[4][5]) (6.5.6).
— The result of subtracting two pointers is not representable in an object of typeptrdiff_t (6.5.6).
— An expression is shifted by a negative number or by an amount greater than or equal
to the width of the promoted expression (6.5.7).
— An expression having signed promoted type is left-shifted and either the value of theexpression is negative or the result of shifting would be not be representable in the
promoted type (6.5.7).
— Pointers that do not point to the same aggregate or union (nor just beyond the samearray object) are compared using relational operators (6.5.8).
— An object is assigned to an inexactly overlapping object or to an exactly overlapping
object with incompatible type (6.5.16.1).
— An expression that is required to be an integer constant expression does not have an
integer type; has operands that are not integer constants, enumeration constants,character constants, sizeof expressions whose results are integer constants, orimmediately-cast floating constants; or contains casts (outside operands to sizeof
operators) other than conversions of arithmetic types to integer types (6.6).
— A constant expression in an initializer is not, or does not evaluate to, one of thefollowing: an arithmetic constant expression, a null pointer constant, an address
constant, or an address constant for an object type plus or minus an integer constant
expression (6.6).
— An arithmetic constant expression does not have arithmetic type; has operands thatare not integer constants, floating constants, enumeration constants, character
constants, or sizeof expressions; or contains casts (outside operands to sizeof
operators) other than conversions of arithmetic types to arithmetic types (6.6).
— The value of an object is accessed by an array-subscript [], member-access . or −>,address &, or indirection * operator or a pointer cast in creating an address constant(6.6).
— An identifier for an object is declared with no linkage and the type of the object isincomplete after its declarator, or after its init-declarator if it has an initializer (6.7).
— A function is declared at block scope with an explicit storage-class specifier otherthan extern (6.7.1).
— A structure or union is defined as containing no named members (6.7.2.1).

§J.2

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WG14/N1256— An attempt is made to access, or generate a pointer to just past, a flexible arraymember of a structure when the referenced object provides no elements for that array(6.7.2.1).
— When the complete type is needed, an incomplete structure or union type is notcompleted in the same scope by another declaration of the tag that defines the content(6.7.2.3).
— An attempt is made to modify an object defined with a const-qualified type throughuse of an lvalue with non-const-qualified type (6.7.3).
— An attempt is made to refer to an object defined with a volatile-qualified type throughuse of an lvalue with non-volatile-qualified type (6.7.3).
— The specification of a function type includes any type qualifiers (6.7.3).
— Two qualified types that are required to be compatible do not have the identicallyqualified version of a compatible type (6.7.3).
— An object which has been modified is accessed through a restrict-qualified pointer toa const-qualified type, or through a restrict-qualified pointer and another pointer thatare not both based on the same object (6.7.3.1).
— A restrict-qualified pointer is assigned a value based on another restricted pointerwhose associated block neither began execution before the block associated with thispointer, nor ended before the assignment (6.7.3.1).
— A function with external linkage is declared with an inline function specifier, but is
not also defined in the same translation unit (6.7.4).
— Two pointer types that are required to be compatible are not identically qualified, orare not pointers to compatible types (6.7.5.1).
— The size expression in an array declaration is not a constant expression and evaluates
at program execution time to a nonpositive value (6.7.5.2).
— In a context requiring two array types to be compatible, they do not have compatible
element types, or their size specifiers evaluate to unequal values (6.7.5.2).
— A declaration of an array parameter includes the keyword static within the [ and] and the corresponding argument does not provide access to the first element of anarray with at least the specified number of elements (6.7.5.3).
— A storage-class specifier or type qualifier modifies the keyword void as a function
parameter type list (6.7.5.3).
— In a context requiring two function types to be compatible, they do not havecompatible return types, or their parameters disagree in use of the ellipsis terminatoror the number and type of parameters (after default argument promotion, when there
is no parameter type list or when one type is specified by a function definition with an
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identifier list) (6.7.5.3).
— The value of an unnamed member of a structure or union is used (6.7.8).
— The initializer for a scalar is neither a single expression nor a single expression
enclosed in braces (6.7.8).
— The initializer for a structure or union object that has automatic storage duration isneither an initializer list nor a single expression that has compatible structure or union
type (6.7.8).
— The initializer for an aggregate or union, other than an array initialized by a string
literal, is not a brace-enclosed list of initializers for its elements or members (6.7.8).
— An identifier with external linkage is used, but in the program there does not exist
exactly one external definition for the identifier, or the identifier is not used and there
exist multiple external definitions for the identifier (6.9).
— A function definition includes an identifier list, but the types of the parameters are notdeclared in a following declaration list (6.9.1).
— An adjusted parameter type in a function definition is not an object type (6.9.1).
— A function that accepts a variable number of arguments is defined without aparameter type list that ends with the ellipsis notation (6.9.1).
— The } that terminates a function is reached, and the value of the function call is usedby the caller (6.9.1).
— An identifier for an object with internal linkage and an incomplete type is declaredwith a tentative definition (6.9.2).
— The token defined is generated during the expansion of a #if or #elif
preprocessing directive, or the use of the defined unary operator does not matchone of the two specified forms prior to macro replacement (6.10.1).
— The #include preprocessing directive that results after expansion does not matchone of the two header name forms (6.10.2).
— The character sequence in an #include preprocessing directive does not start with aletter (6.10.2).
— There are sequences of preprocessing tokens within the list of macro arguments thatwould otherwise act as preprocessing directives (6.10.3).
— The result of the preprocessing operator # is not a valid character string literal(6.10.3.2).
— The result of the preprocessing operator ## is not a valid preprocessing token(6.10.3.3).
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WG14/N1256— The #line preprocessing directive that results after expansion does not match one of
the two well-defined forms, or its digit sequence specifies zero or a number greaterthan 2147483647 (6.10.4).
— A non-STDC #pragma preprocessing directive that is documented as causingtranslation failure or some other form of undefined behavior is encountered (6.10.6).
— A #pragma STDC preprocessing directive does not match one of the well-defined
forms (6.10.6).
— The name of a predefined macro, or the identifier defined, is the subject of a#define or #undef preprocessing directive (6.10.8).
— An attempt is made to copy an object to an overlapping object by use of a libraryfunction, other than as explicitly allowed (e.g., memmove) (clause 7).
— A file with the same name as one of the standard headers, not provided as part of theimplementation, is placed in any of the standard places that are searched for included
source files (7.1.2).
— A header is included within an external declaration or definition (7.1.2).
— A function, object, type, or macro that is specified as being declared or defined bysome standard header is used before any header that declares or defines it is included(7.1.2).
— A standard header is included while a macro is defined with the same name as a
keyword (7.1.2).
— The program attempts to declare a library function itself, rather than via a standard
header, but the declaration does not have external linkage (7.1.2).
— The program declares or defines a reserved identifier, other than as allowed by 7.1.4(7.1.3).
— The program removes the definition of a macro whose name begins with anunderscore and either an uppercase letter or another underscore (7.1.3).
— An argument to a library function has an invalid value or a type not expected by afunction with variable number of arguments (7.1.4).
— The pointer passed to a library function array parameter does not have a value suchthat all address computations and object accesses are valid (7.1.4).
— The macro definition of assert is suppressed in order to access an actual function(7.2).
— The argument to the assert macro does not have a scalar type (7.2).
— The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used inany context other than outside all external declarations or preceding all explicit
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declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2).
— The value of an argument to a character handling function is neither equal to the valueof EOF nor representable as an unsigned char (7.4).
— A macro definition of errno is suppressed in order to access an actual object, or the
program defines an identifier with the name errno (7.5).
— Part of the program tests floating-point status flags, sets floating-point control modes,
or runs under non-default mode settings, but was translated with the state for the
FENV_ACCESS pragma ‘‘off’’ (7.6.1).
— The exception-mask argument for one of the functions that provide access to thefloating-point status flags has a nonzero value not obtained by bitwise OR of thefloating-point exception macros (7.6.2).
— The fesetexceptflag function is used to set floating-point status flags that were
not specified in the call to the fegetexceptflag function that provided the valueof the corresponding fexcept_t object (7.6.2.4).
— The argument to fesetenv or feupdateenv is neither an object set by a call tofegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4).
— The value of the result of an integer arithmetic or conversion function cannot be
represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.20.6.1, 7.20.6.2, 7.20.1).
— The program modifies the string pointed to by the value returned by the setlocale
function (7.11.1.1).
— The program modifies the structure pointed to by the value returned by the
localeconv function (7.11.2.1).
— A macro definition of math_errhandling is suppressed or the program defines
an identifier with the name math_errhandling (7.12).
— An argument to a floating-point classification or comparison macro is not of real
floating type (7.12.3, 7.12.14).
— A macro definition of setjmp is suppressed in order to access an actual function, or
the program defines an external identifier with the name setjmp (7.13).
— An invocation of the setjmp macro occurs other than in an allowed context(7.13.2.1).
— The longjmp function is invoked to restore a nonexistent environment (7.13.2.1).
— After a longjmp, there is an attempt to access the value of an object of automaticstorage class with non-volatile-qualified type, local to the function containing the
invocation of the corresponding setjmp macro, that was changed between the
setjmp invocation and longjmp call (7.13.2.1).
§J.2

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WG14/N1256— The program specifies an invalid pointer to a signal handler function (7.14.1.1).
— A signal handler returns when the signal corresponded to a computational exception(7.14.1.1).
— A signal occurs as the result of calling the abort or raise function, and the signal
handler calls the raise function (7.14.1.1).
— A signal occurs other than as the result of calling the abort or raise function, andthe signal handler refers to an object with static storage duration other than by
assigning a value to an object declared as volatile sig_atomic_t, or calls any
function in the standard library other than the abort function, the _Exit function,or the signal function (for the same signal number) (7.14.1.1).
— The value of errno is referred to after a signal occurred other than as the result of
calling the abort or raise function and the corresponding signal handler obtained
a SIG_ERR return from a call to the signal function (7.14.1.1).
— A signal is generated by an asynchronous signal handler (7.14.1.1).
— A function with a variable number of arguments attempts to access its varying
arguments other than through a properly declared and initialized va_list object, or
before the va_start macro is invoked (7.15, 7.15.1.1, 7.15.1.4).
— The macro va_arg is invoked using the parameter ap that was passed to a functionthat invoked the macro va_arg with the same parameter (7.15).
— A macro definition of va_start, va_arg, va_copy, or va_end is suppressed inorder to access an actual function, or the program defines an external identifier with
the name va_copy or va_end (7.15.1).
— The va_start or va_copy macro is invoked without a corresponding invocationof the va_end macro in the same function, or vice versa (7.15.1, 7.15.1.2, 7.15.1.3,
7.15.1.4).
— The type parameter to the va_arg macro is not such that a pointer to an object ofthat type can be obtained simply by postfixing a * (7.15.1.1).
— The va_arg macro is invoked when there is no actual next argument, or with a
specified type that is not compatible with the promoted type of the actual next
argument, with certain exceptions (7.15.1.1).
— The va_copy or va_start macro is called to initialize a va_list that waspreviously initialized by either macro without an intervening invocation of theva_end macro for the same va_list (7.15.1.2, 7.15.1.4).
— The parameter parmN of a va_start macro is declared with the registerstorage class, with a function or array type, or with a type that is not compatible withthe type that results after application of the default argument promotions (7.15.1.4).
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ISO/IEC 9899:TC3— The member designator parameter of an offsetof macro is an invalid right
operand of the . operator for the type parameter, or designates a bit-field (7.17).
— The argument in an instance of one of the integer-constant macros is not a decimal,
octal, or hexadecimal constant, or it has a value that exceeds the limits for thecorresponding type (7.18.4).
— A byte input/output function is applied to a wide-oriented stream, or a wide character
input/output function is applied to a byte-oriented stream (7.19.2).
— Use is made of any portion of a file beyond the most recent wide character written toa wide-oriented stream (7.19.2).
— The value of a pointer to a FILE object is used after the associated file is closed(7.19.3).
— The stream for the fflush function points to an input stream or to an update stream
in which the most recent operation was input (7.19.5.2).
— The string pointed to by the mode argument in a call to the fopen function does notexactly match one of the specified character sequences (7.19.5.3).
— An output operation on an update stream is followed by an input operation without anintervening call to the fflush function or a file positioning function, or an input
operation on an update stream is followed by an output operation with an intervening
call to a file positioning function (7.19.5.3).
— An attempt is made to use the contents of the array that was supplied in a call to the
setvbuf function (7.19.5.6).
— There are insufficient arguments for the format in a call to one of the formatted
input/output functions, or an argument does not have an appropriate type (7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2).
— The format in a call to one of the formatted input/output functions or to thestrftime or wcsftime function is not a valid multibyte character sequence thatbegins and ends in its initial shift state (7.19.6.1, 7.19.6.2, 7.23.3.5, 7.24.2.1, 7.24.2.2,
7.24.5.1).
— In a call to one of the formatted output functions, a precision appears with aconversion specifier other than those described (7.19.6.1, 7.24.2.1).
— A conversion specification for a formatted output function uses an asterisk to denotean argument-supplied field width or precision, but the corresponding argument is notprovided (7.19.6.1, 7.24.2.1).
— A conversion specification for a formatted output function uses a # or 0 flag with aconversion specifier other than those described (7.19.6.1, 7.24.2.1).
§J.2

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WG14/N1256— A conversion specification for one of the formatted input/output functions uses alength modifier with a conversion specifier other than those described (7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2).
— An s conversion specifier is encountered by one of the formatted output functions,and the argument is missing the null terminator (unless a precision is specified that
does not require null termination) (7.19.6.1, 7.24.2.1).
— An n conversion specification for one of the formatted input/output functions includes
any flags, an assignment-suppressing character, a field width, or a precision (7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2).
— A % conversion specifier is encountered by one of the formatted input/output
functions, but the complete conversion specification is not exactly %% (7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2).
— An invalid conversion specification is found in the format for one of the formatted
input/output functions, or the strftime or wcsftime function (7.19.6.1, 7.19.6.2,
7.23.3.5, 7.24.2.1, 7.24.2.2, 7.24.5.1).
— The number of characters transmitted by a formatted output function is greater than
INT_MAX (7.19.6.1, 7.19.6.3, 7.19.6.8, 7.19.6.10).
— The result of a conversion by one of the formatted input functions cannot be
represented in the corresponding object, or the receiving object does not have anappropriate type (7.19.6.2, 7.24.2.2).
— A c, s, or [ conversion specifier is encountered by one of the formatted input
functions, and the array pointed to by the corresponding argument is not large enoughto accept the input sequence (and a null terminator if the conversion specifier is s or[) (7.19.6.2, 7.24.2.2).
— A c, s, or [ conversion specifier with an l qualifier is encountered by one of theformatted input functions, but the input is not a valid multibyte character sequencethat begins in the initial shift state (7.19.6.2, 7.24.2.2).
— The input item for a %p conversion by one of the formatted input functions is not avalue converted earlier during the same program execution (7.19.6.2, 7.24.2.2).
— The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf,
vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or
vwscanf function is called with an improperly initialized va_list argument, orthe argument is used (other than in an invocation of va_end) after the function
returns (7.19.6.8, 7.19.6.9, 7.19.6.10, 7.19.6.11, 7.19.6.12, 7.19.6.13, 7.19.6.14,
7.24.2.5, 7.24.2.6, 7.24.2.7, 7.24.2.8, 7.24.2.9, 7.24.2.10).
— The contents of the array supplied in a call to the fgets, gets, or fgetws function
are used after a read error occurred (7.19.7.2, 7.19.7.7, 7.24.3.2).
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ISO/IEC 9899:TC3— The file position indicator for a binary stream is used after a call to the ungetc
function where its value was zero before the call (7.19.7.11).
— The file position indicator for a stream is used after an error occurred during a call to
the fread or fwrite function (7.19.8.1, 7.19.8.2).
— A partial element read by a call to the fread function is used (7.19.8.1).
— The fseek function is called for a text stream with a nonzero offset and either theoffset was not returned by a previous successful call to the ftell function on a
stream associated with the same file or whence is not SEEK_SET (7.19.9.2).
— The fsetpos function is called to set a position that was not returned by a previous
successful call to the fgetpos function on a stream associated with the same file
(7.19.9.3).
— A non-null pointer returned by a call to the calloc, malloc, or realloc function
with a zero requested size is used to access an object (7.20.3).
— The value of a pointer that refers to space deallocated by a call to the free orrealloc function is used (7.20.3).
— The pointer argument to the free or realloc function does not match a pointerearlier returned by calloc, malloc, or realloc, or the space has been
deallocated by a call to free or realloc (7.20.3.2, 7.20.3.4).
— The value of the object allocated by the malloc function is used (7.20.3.3).
— The value of any bytes in a new object allocated by the realloc function beyond
the size of the old object are used (7.20.3.4).
— The program executes more than one call to the exit function (7.20.4.3).
— During the call to a function registered with the atexit function, a call is made to
the longjmp function that would terminate the call to the registered function(7.20.4.3).
— The string set up by the getenv or strerror function is modified by the program(7.20.4.5, 7.21.6.2).
— A command is executed through the system function in a way that is documented as
causing termination or some other form of undefined behavior (7.20.4.6).
— A searching or sorting utility function is called with an invalid pointer argument, even
if the number of elements is zero (7.20.5).
— The comparison function called by a searching or sorting utility function alters thecontents of the array being searched or sorted, or returns ordering values
inconsistently (7.20.5).

§J.2

Portability issues503

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

WG14/N1256— The array being searched by the bsearch function does not have its elements inproper order (7.20.5.1).
— The current conversion state is used by a multibyte/wide character conversion
function after changing the LC_CTYPE category (7.20.7).
— A string or wide string utility function is instructed to access an array beyond the endof an object (7.21.1, 7.24.4).
— A string or wide string utility function is called with an invalid pointer argument, even
if the length is zero (7.21.1, 7.24.4).
— The contents of the destination array are used after a call to the strxfrm,
strftime, wcsxfrm, or wcsftime function in which the specified length was
too small to hold the entire null-terminated result (7.21.4.5, 7.23.3.5, 7.24.4.4.4,
7.24.5.1).
— The first argument in the very first call to the strtok or wcstok is a null pointer(7.21.5.8, 7.24.4.5.7).
— The type of an argument to a type-generic macro is not compatible with the type ofthe corresponding parameter of the selected function (7.22).
— A complex argument is supplied for a generic parameter of a type-generic macro thathas no corresponding complex function (7.22).
— The argument corresponding to an s specifier without an l qualifier in a call to the
fwprintf function does not point to a valid multibyte character sequence thatbegins in the initial shift state (7.24.2.11).
— In a call to the wcstok function, the object pointed to by ptr does not have thevalue stored by the previous call for the same wide string (7.24.4.5.7).
— An mbstate_t object is used inappropriately (7.24.6).
— The value of an argument of type wint_t to a wide character classification or casemapping function is neither equal to the value of WEOF nor representable as awchar_t (7.25.1).
— The iswctype function is called using a different LC_CTYPE category from theone in effect for the call to the wctype function that returned the description(7.25.2.2.1).
— The towctrans function is called using a different LC_CTYPE category from theone in effect for the call to the wctrans function that returned the description(7.25.3.2.1).

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ISO/IEC 9899:TC3

J.3 Implementation-defined behavior
1

A conforming implementation is required to document its choice of behavior in each of
the areas listed in this subclause. The following are implementation-defined:

J.3.1 Translation
1— How a diagnostic is identified (3.10, 5.1.1.3).
— Whether each nonempty sequence of white-space characters other than new-line isretained or replaced by one space character in translation phase 3 (5.1.1.2).

J.3.2 Environment
1— The mapping between physical source file multibyte characters and the source
character set in translation phase 1 (5.1.1.2).
— The name and type of the function called at program startup in a freestanding
environment (5.1.2.1).
— The effect of program termination in a freestanding environment (5.1.2.1).
— An alternative manner in which the main function may be defined (5.1.2.2.1).
— The values given to the strings pointed to by the argv argument to main (5.1.2.2.1).
— What constitutes an interactive device (5.1.2.3).
— The set of signals, their semantics, and their default handling (7.14).
— Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to acomputational exception (7.14.1.1).
— Signals for which the equivalent of signal(sig, SIG_IGN); is executed at
program startup (7.14.1.1).
— The set of environment names and the method for altering the environment list usedby the getenv function (7.20.4.5).
— The manner of execution of the string by the system function (7.20.4.6).

J.3.3 Identifiers
1— Which additional multibyte characters may appear in identifiers and theircorrespondence to universal character names (6.4.2).
— The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).

§J.3.3

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WG14/N1256

J.3.4 Characters
1— The number of bits in a byte (3.6).
— The values of the members of the execution character set (5.2.1).
— The unique value of the member of the execution character set produced for each of
the standard alphabetic escape sequences (5.2.2).
— The value of a char object into which has been stored any character other than amember of the basic execution character set (6.2.5).
— Which of signed char or unsigned char has the same range, representation,and behavior as ‘‘plain’’ char (6.2.5, 6.3.1.1).
— The mapping of members of the source character set (in character constants and string
literals) to members of the execution character set (6.4.4.4, 5.1.1.2).
— The value of an integer character constant containing more than one character orcontaining a character or escape sequence that does not map to a single-byte
execution character (6.4.4.4).
— The value of a wide character constant containing more than one multibyte character,or containing a multibyte character or escape sequence not represented in theextended execution character set (6.4.4.4).
— The current locale used to convert a wide character constant consisting of a single
multibyte character that maps to a member of the extended execution character set
into a corresponding wide character code (6.4.4.4).
— The current locale used to convert a wide string literal into corresponding wide
character codes (6.4.5).
— The value of a string literal containing a multibyte character or escape sequence notrepresented in the execution character set (6.4.5).

J.3.5 Integers
1— Any extended integer types that exist in the implementation (6.2.5).
— Whether signed integer types are represented using sign and magnitude, two’s
complement, or ones’ complement, and whether the extraordinary value is a trap
representation or an ordinary value (6.2.6.2).

— The rank of any extended integer type relative to another extended integer type withthe same precision (6.3.1.1).
— The result of, or the signal raised by, converting an integer to a signed integer typewhen the value cannot be represented in an object of that type (6.3.1.3).

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ISO/IEC 9899:TC3— The results of some bitwise operations on signed integers (6.5).

J.3.6 Floating point1— The accuracy of the floating-point operations and of the library functions in<math.h> and <complex.h> that return floating-point results (5.2.4.2.2).
— The accuracy of the conversions between floating-point internal representations andstring representations performed by the library functions in <stdio.h>,<stdlib.h>, and <wchar.h> (5.2.4.2.2).

— The rounding behaviors characterized by non-standard values of FLT_ROUNDS(5.2.4.2.2).
— The evaluation methods characterized by non-standard negative values of
FLT_EVAL_METHOD (5.2.4.2.2).
— The direction of rounding when an integer is converted to a floating-point number thatcannot exactly represent the original value (6.3.1.4).
— The direction of rounding when a floating-point number is converted to a narrower
floating-point number (6.3.1.5).
— How the nearest representable value or the larger or smaller representable value
immediately adjacent to the nearest representable value is chosen for certain floating
constants (6.4.4.2).
— Whether and how floating expressions are contracted when not disallowed by the
FP_CONTRACT pragma (6.5).
— The default state for the FENV_ACCESS pragma (7.6.1).
— Additional floating-point exceptions, roundingclassifications, and their macro names (7.6, 7.12).

modes,

environments,

and∗— The default state for the FP_CONTRACT pragma (7.12.2).

J.3.7 Arrays and pointers
1— The result of converting a pointer to an integer or vice versa (6.3.2.3).
— The size of the result of subtracting two pointers to elements of the same array(6.5.6).

§J.3.7

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WG14/N1256

J.3.8 Hints
1— The extent to which suggestions made by using the register storage-classspecifier are effective (6.7.1).
— The extent to which suggestions made by using the inline function specifier are
effective (6.7.4).

J.3.9 Structures, unions, enumerations, and bit-fields
1— Whether a ‘‘plain’’ int bit-field is treated as a signed int bit-field or as an
unsigned int bit-field (6.7.2, 6.7.2.1).
— Allowable bit-field types other than _Bool, signed int, and unsigned int(6.7.2.1).
— Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).
— The order of allocation of bit-fields within a unit (6.7.2.1).
— The alignment of non-bit-field members of structures (6.7.2.1). This should present
no problem unless binary data written by one implementation is read by another.
— The integer type compatible with each enumerated type (6.7.2.2).

J.3.10 Qualifiers
1— What constitutes an access to an object that has volatile-qualified type (6.7.3).

J.3.11 Preprocessing directives
1— The locations within #pragma directives where header name preprocessing tokens
are recognized (6.4, 6.4.7).

— How sequences in both forms of header names are mapped to headers or externalsource file names (6.4.7).
— Whether the value of a character constant in a constant expression that controls
conditional inclusion matches the value of the same character constant in theexecution character set (6.10.1).
— Whether the value of a single-character character constant in a constant expressionthat controls conditional inclusion may have a negative value (6.10.1).
— The places that are searched for an included < > delimited header, and how the places
are specified or the header is identified (6.10.2).
— How the named source file is searched for in an included " " delimited header(6.10.2).
— The method by which preprocessing tokens (possibly resulting from macro
expansion) in a #include directive are combined into a header name (6.10.2).
508

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ISO/IEC 9899:TC3— The nesting limit for #include processing (6.10.2).
— Whether the # operator inserts a \ character before the \ character that begins auniversal character name in a character constant or string literal (6.10.3.2).
— The behavior on each recognized non-STDC #pragma directive (6.10.6).
— The definitions for _ _DATE_ _ and _ _TIME_ _ when respectively, the date andtime of translation are not available (6.10.8).

J.3.12 Library functions
1— Any library facilities available to a freestanding program, other than the minimal set
required by clause 4 (5.1.2.1).
— The format of the diagnostic printed by the assert macro (7.2.1.1).
— The representation of the floating-point
fegetexceptflag function (7.6.2.2).

statusflags

storedbythe— Whether the feraiseexcept function raises the ‘‘inexact’’ floating-point
exception in addition to the ‘‘overflow’’ or ‘‘underflow’’ floating-point exception(7.6.2.3).
— Strings other than "C" and "" that may be passed as the second argument to thesetlocale function (7.11.1.1).
— The types defined for float_t and double_t when the value of the
FLT_EVAL_METHOD macro is less than 0 (7.12).

— Domain errors for the mathematics functions, other than those required by thisInternational Standard (7.12.1).
— The values returned by the mathematics functions on domain errors (7.12.1).
— The values returned by the mathematics functions on underflow range errors, whether
errno is set to the value of the macro ERANGE when the integer expression
math_errhandling & MATH_ERRNO is nonzero, and whether the ‘‘underflow’’floating-point exception is raised when the integer expression math_errhandling& MATH_ERREXCEPT is nonzero. (7.12.1).
— Whether a domain error occurs or zero is returned when an fmod function has asecond argument of zero (7.12.10.1).
— Whether a domain error occurs or zero is returned when a remainder function has
a second argument of zero (7.12.10.2).

— The base-2 logarithm of the modulus used by the remquo functions in reducing thequotient (7.12.10.3).

§J.3.12

Portability issues509

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

WG14/N1256— Whether a domain error occurs or zero is returned when a remquo function has asecond argument of zero (7.12.10.3).

— Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the callof a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).
— The null pointer constant to which the macro NULL expands (7.17).
— Whether the last line of a text stream requires a terminating new-line character(7.19.2).
— Whether space characters that are written out to a text stream immediately before a
new-line character appear when read in (7.19.2).
— The number of null characters that may be appended to data written to a binary
stream (7.19.2).
— Whether the file position indicator of an append-mode stream is initially positioned at
the beginning or end of the file (7.19.3).
— Whether a write on a text stream causes the associated file to be truncated beyond thatpoint (7.19.3).
— The characteristics of file buffering (7.19.3).
— Whether a zero-length file actually exists (7.19.3).
— The rules for composing valid file names (7.19.3).
— Whether the same file can be simultaneously open multiple times (7.19.3).
— The nature and choice of encodings used for multibyte characters in files (7.19.3).
— The effect of the remove function on an open file (7.19.4.1).
— The effect if a file with the new name exists prior to a call to the rename function(7.19.4.2).
— Whether an open temporary file is removed upon abnormal program termination(7.19.4.3).
— Which changes of mode are permitted (if any), and under what circumstances(7.19.5.4).
— The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar
sequence printed for a NaN (7.19.6.1, 7.24.2.1).
— The output for %p conversion in the fprintf or fwprintf function (7.19.6.1,
7.24.2.1).
— The interpretation of a - character that is neither the first nor the last character, nor
the second where a ^ character is the first, in the scanlist for %[ conversion in the
fscanf or fwscanf function (7.19.6.2, 7.24.2.1).
510
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WG14/N1256

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ISO/IEC 9899:TC3— The set of sequences matched by a %p conversion and the interpretation of thecorresponding input item in the fscanf or fwscanf function (7.19.6.2, 7.24.2.2).
— The value to which the macro errno is set by the fgetpos, fsetpos, or ftellfunctions on failure (7.19.9.1, 7.19.9.3, 7.19.9.4).
— The meaning of any n-char or n-wchar sequence in a string representing a NaN that isconverted by the strtod, strtof, strtold, wcstod, wcstof, or wcstoldfunction (7.20.1.3, 7.24.4.1.1).
— Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstoldfunction sets errno to ERANGE when underflow occurs (7.20.1.3, 7.24.4.1.1).
— Whether the calloc, malloc, and realloc functions return a null pointer or apointer to an allocated object when the size requested is zero (7.20.3).
— Whether open streams with unwritten buffered data are flushed, open streams areclosed, or temporary files are removed when the abort or _Exit function is called(7.20.4.1, 7.20.4.4).
— The termination status returned to the host environment by the abort, exit, or_Exit function (7.20.4.1, 7.20.4.3, 7.20.4.4).
— The value returned by the system function when its argument is not a null pointer(7.20.4.6).
— The local time zone and Daylight Saving Time (7.23.1).
— The range and precision of times representable in clock_t and time_t (7.23).
— The era for the clock function (7.23.2.1).
— The replacement string for the %Z specifier to the strftime, and wcsftime
functions in the "C" locale (7.23.3.5, 7.24.5.1).
— Whether the functions in <math.h> honor the rounding direction mode in an
IEC 60559 conformant implementation, unless explicitly specified otherwise (F.9).

J.3.13 Architecture
1— The values or expressions assigned to the macros specified in the headers<float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.18.2, 7.18.3).
— The number, order, and encoding of bytes in any object (when not explicitly specified
in this International Standard) (6.2.6.1).
— The value of the result of the sizeof operator (6.5.3.4).

§J.3.13

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J.4 Locale-specific behavior
1

The following characteristics of a hosted environment are locale-specific and are required
to be documented by the implementation:— Additional members of the source and execution character sets beyond the basic
character set (5.2.1).
— The presence, meaning, and representation of additional multibyte characters in theexecution character set beyond the basic character set (5.2.1.2).
— The shift states used for the encoding of multibyte characters (5.2.1.2).
— The direction of writing of successive printing characters (5.2.2).
— The decimal-point character (7.1.1).
— The set of printing characters (7.4, 7.25.2).
— The set of control characters (7.4, 7.25.2).
— The sets of characters tested for by the isalpha, isblank, islower, ispunct,isspace, isupper, iswalpha, iswblank, iswlower, iswpunct,iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10,
7.4.1.11, 7.25.2.1.2, 7.25.2.1.3, 7.25.2.1.7, 7.25.2.1.9, 7.25.2.1.10, 7.25.2.1.11).
— The native environment (7.11.1.1).
— Additional subject sequences accepted by the numeric conversion functions (7.20.1,
7.24.4.1).
— The collation sequence of the execution character set (7.21.4.3, 7.24.4.4.2).
— The contents of the error message strings set up by the strerror function(7.21.6.2).
— The formats for time and date (7.23.3.5, 7.24.5.1).
— Character mappings that are supported by the towctrans function (7.25.1).
— Character classifications that are supported by the iswctype function (7.25.1).

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J.5 Common extensions
1

The following extensions are widely used in many systems, but are not portable to all
implementations. The inclusion of any extension that may cause a strictly conforming
program to become invalid renders an implementation nonconforming. Examples of suchextensions are new keywords, extra library functions declared in standard headers, orpredefined macros with names that do not begin with an underscore.

J.5.1 Environment arguments
1

In a hosted environment, the main function receives a third argument, char *envp[],
that points to a null-terminated array of pointers to char, each of which points to a stringthat provides information about the environment for this execution of the program(5.1.2.2.1).

J.5.2 Specialized identifiers
1

Characters other than the underscore _, letters, and digits, that are not part of the basic
source character set (such as the dollar sign $, or characters in national character sets)
may appear in an identifier (6.4.2).

J.5.3 Lengths and cases of identifiers
1

All characters in identifiers (with or without external linkage) are significant (6.4.2).

J.5.4 Scopes of identifiers
1

A function identifier, or the identifier of an object the declaration of which contains the
keyword extern, has file scope (6.2.1).

J.5.5 Writable string literals
1String literals are modifiable (in which case, identical string literals should denote distinct
objects) (6.4.5).

J.5.6 Other arithmetic types
1

Additional arithmetic types, such as _ _int128 or double double, and theirappropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may havemore range or precision than long double, may be used for evaluating expressions ofother floating types, and may be used to define float_t or double_t.

§J.5.6

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J.5.7 Function pointer casts
1

A pointer to an object or to void may be cast to a pointer to a function, allowing data to
be invoked as a function (6.5.4).

2

A pointer to a function may be cast to a pointer to an object or to void, allowing afunction to be inspected or modified (for example, by a debugger) (6.5.4).

J.5.8 Extended bit-field types
1

A bit-field may be declared with a type other than _Bool, unsigned int, or
signed int, with an appropriate maximum width (6.7.2.1).

J.5.9 The fortran keyword
1

The fortran function specifier may be used in a function declaration to indicate that
calls suitable for FORTRAN should be generated, or that a different representation for theexternal name is to be generated (6.7.4).

J.5.10 The asm keyword
1

The asm keyword may be used to insert assembly language directly into the translator
output (6.8). The most common implementation is via a statement of the form:
asm ( character-string-literal );J.5.11 Multiple external definitions
1

There may be more than one external definition for the identifier of an object, with orwithout the explicit use of the keyword extern; if the definitions disagree, or more than
one is initialized, the behavior is undefined (6.9.2).

J.5.12 Predefined macro names
1

Macro names that do not begin with an underscore, describing the translation andexecution environments, are defined by the implementation before translation begins(6.10.8).

J.5.13 Floating-point status flags
1

If any floating-point status flags are set on normal termination after all calls to functions
registered by the atexit function have been made (see 7.20.4.3), the implementation
writes some diagnostics indicating the fact to the stderr stream, if it is still open,

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J.5.14 Extra arguments for signal handlers
1

Handlers for specific signals are called with extra arguments in addition to the signal
number (7.14.1.1).

J.5.15 Additional stream types and file-opening modes
1

Additional mappings from files to streams are supported (7.19.2).

2

Additional file-opening modes may be specified by characters appended to the modeargument of the fopen function (7.19.5.3).

J.5.16 Defined file position indicator
1

The file position indicator is decremented by each successful call to the ungetc orungetwc function for a text stream, except if its value was zero before a call (7.19.7.11,
7.24.3.10).

J.5.17 Math error reporting
1

Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors
instead of, or in addition to, setting errno or raising floating-point exceptions (7.3,
7.12).

§J.5.17

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Bibliography
1.

‘‘The C Reference Manual’’ by Dennis M. Ritchie, a version of which was
published in The C Programming Language by Brian W. Kernighan and Dennis
M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T.

2.

1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara,
California, USA, November 1984.

3.

ANSI X3/TR−1−82 (1982), American National Dictionary for Information
Processing Systems, Information Processing Systems Technical Report.

4.

ANSI/IEEE 754−1985, American National Standard for Binary Floating-Point
Arithmetic.

5.

ANSI/IEEE 854−1988, American National Standard for Radix-Independent
Floating-Point Arithmetic.

6.

IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems,
second edition (previously designated IEC 559:1989).

7.

ISO 31−11:1992, Quantities and units — Part 11: Mathematical signs andsymbols for use in the physical sciences and technology.

8.

ISO/IEC 646:1991, Information technology — ISO 7-bit coded character set for
information interchange.

9.

ISO/IEC 2382−1:1993, Information technology — Vocabulary — Part 1:
Fundamental terms.

10.

ISO 4217:1995, Codes for the representation of currencies and funds.

11.

ISO 8601:1988, Data elements and interchange formats — Informationinterchange — Representation of dates and times.

12.

ISO/IEC 9899:1990, Programming languages — C.

13.

ISO/IEC 9899/COR1:1994, Technical Corrigendum 1.

14.

ISO/IEC 9899/COR2:1996, Technical Corrigendum 2.

15.

ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity.

16.

ISO/IEC 9945−2:1993, Information technology — Portable Operating System
Interface (POSIX) — Part 2: Shell and Utilities.

17.

ISO/IEC TR 10176:1998, Information technology — Guidelines for the
preparation of programming language standards.

18.

ISO/IEC 10646-1:1993, Information technology — Universal Multiple-Octet
Coded Character Set (UCS) — Part 1: Architecture and Basic Multilingual Plane.

516

Bibliography

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ISO/IEC 9899:TC3

19.

ISO/IEC 10646-1/COR1:1996,
ISO/IEC 10646-1:1993.

Technical

Corrigendum

1

to

20.

ISO/IEC 10646-1/COR2:1998,
ISO/IEC 10646-1:1993.

Technical

Corrigendum

2

to

21.

ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993
Transformation Format for 16 planes of group 00 (UTF-16).

22.

ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS
Transformation Format 8 (UTF-8).

23.

ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993.

24.

ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993.

25.

ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul
syllables.

26.

ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993 Tibetan.

27.

ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33
additional characters.

28.

ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993.

29.

ISO/IEC 10646-1/AMD9:1997,
Identifiers for characters.

30.

ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993
Ethiopic.

31.

ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993
Unified Canadian Aboriginal Syllabics.

32.

ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993
Cherokee.

33.

ISO/IEC 10967−1:1994, Information technology — Language independent
arithmetic — Part 1: Integer and floating point arithmetic.

Amendment

Bibliography

9

to

ISO/IEC 10646-1:1993

517

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ISO/IEC 9899:TC3

Index
 x , 3.18
 x , 3.19

, (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,
6.7.2.3, 6.7.8− (subtraction operator), 6.5.6, F.3, G.5.2− (unary minus operator), 6.5.3.3, F.3−− (postfix decrement operator), 6.3.2.1, 6.5.2.4−− (prefix decrement operator), 6.3.2.1, 6.5.3.1−= (subtraction assignment operator), 6.5.16.2−> (structure/union pointer operator), 6.5.2.3. (structure/union member operator), 6.3.2.1,
6.5.2.3. punctuator, 6.7.8... (ellipsis punctuator), 6.5.2.2, 6.7.5.3, 6.10.3/ (division operator), 6.5.5, F.3, G.5.1/* */ (comment delimiters), 6.4.9// (comment delimiter), 6.4.9/= (division assignment operator), 6.5.16.2: (colon punctuator), 6.7.2.1:> (alternative spelling of ]), 6.4.6; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3,
6.8.5, 6.8.6< (less-than operator), 6.5.8<% (alternative spelling of {), 6.4.6<: (alternative spelling of [), 6.4.6<< (left-shift operator), 6.5.7<<= (left-shift assignment operator), 6.5.16.2<= (less-than-or-equal-to operator), 6.5.8<assert.h> header, 7.2, B.1<complex.h> header, 5.2.4.2.2, 7.3, 7.22,
7.26.1, G.6, J.5.17<ctype.h> header, 7.4, 7.26.2<errno.h> header, 7.5, 7.26.3<fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F,H<float.h> header, 4, 5.2.4.2.2, 7.7, 7.20.1.3,
7.24.4.1.1<inttypes.h> header, 7.8, 7.26.4<iso646.h> header, 4, 7.9<limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10
<locale.h> header, 7.11, 7.26.5<math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.22, F,
F.9, J.5.17<setjmp.h> header, 7.13
<signal.h> header, 7.14, 7.26.6<stdarg.h> header, 4, 6.7.5.3, 7.15
<stdbool.h> header, 4, 7.16, 7.26.7, H<stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
6.4.5, 6.5.3.4, 6.5.6, 7.17
<stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8,
7.18, 7.26.8! (logical negation operator), 6.5.3.3!= (inequality operator), 6.5.9# operator, 6.10.3.2# preprocessing directive, 6.10.7# punctuator, 6.10## operator, 6.10.3.3#define preprocessing directive, 6.10.3#elif preprocessing directive, 6.10.1#else preprocessing directive, 6.10.1#endif preprocessing directive, 6.10.1#error preprocessing directive, 4, 6.10.5#if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,
6.10.1, 7.1.4#ifdef preprocessing directive, 6.10.1#ifndef preprocessing directive, 6.10.1#include preprocessing directive, 5.1.1.2,
6.10.2#line preprocessing directive, 6.10.4#pragma preprocessing directive, 6.10.6#undef preprocessing directive, 6.10.3.5, 7.1.3,
7.1.4% (remainder operator), 6.5.5%: (alternative spelling of #), 6.4.6%:%: (alternative spelling of ##), 6.4.6%= (remainder assignment operator), 6.5.16.2%> (alternative spelling of }), 6.4.6& (address operator), 6.3.2.1, 6.5.3.2& (bitwise AND operator), 6.5.10&& (logical AND operator), 6.5.13&= (bitwise AND assignment operator), 6.5.16.2' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,
7.4.1.10, 7.25.2.1.3( ) (cast operator), 6.5.4( ) (function-call operator), 6.5.2.2( ) (parentheses punctuator), 6.7.5.3, 6.8.4, 6.8.5( ){ } (compound-literal operator), 6.5.2.5* (asterisk punctuator), 6.7.5.1, 6.7.5.2* (indirection operator), 6.5.2.1, 6.5.3.2* (multiplication operator), 6.5.5, F.3, G.5.1*= (multiplication assignment operator), 6.5.16.2+ (addition operator), 6.5.2.1, 6.5.3.2, 6.5.6, F.3,
G.5.2
+ (unary plus operator), 6.5.3.3++ (postfix increment operator), 6.3.2.1, 6.5.2.4++ (prefix increment operator), 6.3.2.1, 6.5.3.1+= (addition assignment operator), 6.5.16.2, (comma operator), 6.5.17

Index

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_ _cplusplus macro, 6.10.8_ _DATE_ _ macro, 6.10.8_ _FILE_ _ macro, 6.10.8, 7.2.1.1_ _func_ _ identifier, 6.4.2.2, 7.2.1.1_ _LINE_ _ macro, 6.10.8, 7.2.1.1_ _STDC_, 6.11.9_ _STDC_ _ macro, 6.10.8_ _STDC_CONSTANT_MACROS macro, 7.18.4_ _STDC_FORMAT_MACROS macro, 7.8.1_ _STDC_HOSTED_ _ macro, 6.10.8_ _STDC_IEC_559_ _ macro, 6.10.8, F.1_ _STDC_IEC_559_COMPLEX_ _ macro,
6.10.8, G.1_ _STDC_ISO_10646_ _ macro, 6.10.8_ _STDC_LIMIT_MACROS macro, 7.18.2,
7.18.3_ _STDC_MB_MIGHT_NEQ_WC_ _ macro,
6.10.8, 7.17
_ _STDC_VERSION_ _ macro, 6.10.8_ _TIME_ _ macro, 6.10.8_ _VA_ARGS_ _ identifier, 6.10.3, 6.10.3.1_Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2_Bool type conversions, 6.3.1.2_Complex types, 6.2.5, 6.7.2, 7.3.1, G_Complex_I macro, 7.3.1_Exit function, 7.20.4.4_Imaginary keyword, G.2_Imaginary types, 7.3.1, G_Imaginary_I macro, 7.3.1, G.6_IOFBF macro, 7.19.1, 7.19.5.5, 7.19.5.6_IOLBF macro, 7.19.1, 7.19.5.6_IONBF macro, 7.19.1, 7.19.5.5, 7.19.5.6_Pragma operator, 5.1.1.2, 6.10.9{ } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.8,
6.8.2{ } (compound-literal operator), 6.5.2.5| (bitwise inclusive OR operator), 6.5.12|= (bitwise inclusive OR assignment operator),
6.5.16.2|| (logical OR operator), 6.5.14~ (bitwise complement operator), 6.5.3.3<stdio.h> header, 5.2.4.2.2, 7.19, 7.26.9, F<stdlib.h> header, 5.2.4.2.2, 7.20, 7.26.10, F<string.h> header, 7.21, 7.26.11<tgmath.h> header, 7.22, G.7<time.h> header, 7.23
<wchar.h> header, 5.2.4.2.2, 7.19.1, 7.24,
7.26.12, F<wctype.h> header, 7.25, 7.26.13= (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.8= (simple assignment operator), 6.5.16.1== (equality operator), 6.5.9> (greater-than operator), 6.5.8>= (greater-than-or-equal-to operator), 6.5.8>> (right-shift operator), 6.5.7>>= (right-shift assignment operator), 6.5.16.2? : (conditional operator), 6.5.15?? (trigraph sequences), 5.2.1.1[ ] (array subscript operator), 6.5.2.1, 6.5.3.2[ ] (brackets punctuator), 6.7.5.2, 6.7.8\ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4\ (escape character), 6.4.4.4\" (double-quote escape sequence), 6.4.4.4,
6.4.5, 6.10.9\\ (backslash escape sequence), 6.4.4.4, 6.10.9\' (single-quote escape sequence), 6.4.4.4, 6.4.5\0 (null character), 5.2.1, 6.4.4.4, 6.4.5
padding of binary stream, 7.19.2\? (question-mark escape sequence), 6.4.4.4\a (alert escape sequence), 5.2.2, 6.4.4.4\b (backspace escape sequence), 5.2.2, 6.4.4.4\f (form-feed escape sequence), 5.2.2, 6.4.4.4,
7.4.1.10\n (new-line escape sequence), 5.2.2, 6.4.4.4,
7.4.1.10\octal digits (octal-character escape sequence),
6.4.4.4\r (carriage-return escape sequence), 5.2.2,
6.4.4.4, 7.4.1.10\t (horizontal-tab escape sequence), 5.2.2,
6.4.4.4, 7.4.1.3, 7.4.1.10, 7.25.2.1.3\U (universal character names), 6.4.3\u (universal character names), 6.4.3\v (vertical-tab escape sequence), 5.2.2, 6.4.4.4,
7.4.1.10\x hexadecimal digits (hexadecimal-character
escape sequence), 6.4.4.4^ (bitwise exclusive OR operator), 6.5.11^= (bitwise exclusive OR assignment operator),
6.5.16.2_ _bool_true_false_are_definedmacro, 7.16

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abort function, 7.2.1.1, 7.14.1.1, 7.19.3,
7.20.4.1
abs function, 7.20.6.1
absolute-value functions
complex, 7.3.8, G.6.4
integer, 7.8.2.1, 7.20.6.1
real, 7.12.7, F.9.4
abstract declarator, 6.7.6
abstract machine, 5.1.2.3

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

access, 3.1, 6.7.3
accuracy, see floating-point accuracy
acos functions, 7.12.4.1, F.9.1.1
acos type-generic macro, 7.22
acosh functions, 7.12.5.1, F.9.2.1
acosh type-generic macro, 7.22
active position, 5.2.2
actual argument, 3.3
actual parameter (deprecated), 3.3
addition assignment operator (+=), 6.5.16.2
addition operator (+), 6.5.2.1, 6.5.3.2, 6.5.6, F.3,
G.5.2
additive expressions, 6.5.6, G.5.2
address constant, 6.6
address operator (&), 6.3.2.1, 6.5.3.2
aggregate initialization, 6.7.8
aggregate types, 6.2.5
alert escape sequence (\a), 5.2.2, 6.4.4.4
aliasing, 6.5
alignment, 3.2
pointer, 6.2.5, 6.3.2.3
structure/union member, 6.7.2.1
allocated storage, order and contiguity, 7.20.3
and macro, 7.9
AND operators
bitwise (&), 6.5.10
bitwise assignment (&=), 6.5.16.2
logical (&&), 6.5.13
and_eq macro, 7.9
ANSI/IEEE 754, F.1
ANSI/IEEE 854, F.1
argc (main function parameter), 5.1.2.2.1
argument, 3.3
array, 6.9.1
default promotions, 6.5.2.2
function, 6.5.2.2, 6.9.1
macro, substitution, 6.10.3.1
argument, complex, 7.3.9.1
argv (main function parameter), 5.1.2.2.1
arithmetic constant expression, 6.6
arithmetic conversions, usual, see usual arithmetic
conversions
arithmetic operators
additive, 6.5.6, G.5.2
bitwise, 6.5.10, 6.5.11, 6.5.12
increment and decrement, 6.5.2.4, 6.5.3.1
multiplicative, 6.5.5, G.5.1
shift, 6.5.7
unary, 6.5.3.3
arithmetic types, 6.2.5
arithmetic, pointer, 6.5.6

ISO/IEC 9899:TC3

array
argument, 6.9.1
declarator, 6.7.5.2
initialization, 6.7.8
multidimensional, 6.5.2.1
parameter, 6.9.1
storage order, 6.5.2.1
subscript operator ([ ]), 6.5.2.1, 6.5.3.2
subscripting, 6.5.2.1
type, 6.2.5
type conversion, 6.3.2.1
variable length, 6.7.5, 6.7.5.2
arrow operator (−>), 6.5.2.3
as−if rule, 5.1.2.3
ASCII code set, 5.2.1.1
asctime function, 7.23.3.1
asin functions, 7.12.4.2, F.9.1.2
asin type-generic macro, 7.22, G.7
asinh functions, 7.12.5.2, F.9.2.2
asinh type-generic macro, 7.22, G.7
asm keyword, J.5.10
assert macro, 7.2.1.1
assert.h header, 7.2, B.1
assignment
compound, 6.5.16.2
conversion, 6.5.16.1
expression, 6.5.16
operators, 6.3.2.1, 6.5.16
simple, 6.5.16.1
associativity of operators, 6.5
asterisk punctuator (*), 6.7.5.1, 6.7.5.2
atan functions, 7.12.4.3, F.9.1.3
atan type-generic macro, 7.22, G.7
atan2 functions, 7.12.4.4, F.9.1.4
atan2 type-generic macro, 7.22
atanh functions, 7.12.5.3, F.9.2.3
atanh type-generic macro, 7.22, G.7
atexit function, 7.20.4.2, 7.20.4.3, 7.20.4.4,
J.5.13
atof function, 7.20.1, 7.20.1.1
atoi function, 7.20.1, 7.20.1.2
atol function, 7.20.1, 7.20.1.2
atoll function, 7.20.1, 7.20.1.2
auto storage-class specifier, 6.7.1, 6.9
automatic storage duration, 5.2.3, 6.2.4

backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
backslash escape sequence (\\), 6.4.4.4, 6.10.9
backspace escape sequence (\b), 5.2.2, 6.4.4.4
basic character set, 3.6, 3.7.2, 5.2.1
basic types, 6.2.5

Index

521

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

behavior, 3.4
binary streams, 7.19.2, 7.19.7.11, 7.19.9.2,
7.19.9.4
bit, 3.5
high order, 3.6
low order, 3.6
bit-field, 6.7.2.1
bitand macro, 7.9
bitor macro, 7.9
bitwise operators, 6.5
AND, 6.5.10
AND assignment (&=), 6.5.16.2
complement (~), 6.5.3.3
exclusive OR, 6.5.11
exclusive OR assignment (^=), 6.5.16.2
inclusive OR, 6.5.12
inclusive OR assignment (|=), 6.5.16.2
shift, 6.5.7
blank character, 7.4.1.3
block, 6.8, 6.8.2, 6.8.4, 6.8.5
block scope, 6.2.1
block structure, 6.2.1
bold type convention, 6.1
bool macro, 7.16
boolean type, 6.3.1.2
boolean type conversion, 6.3.1.1, 6.3.1.2
braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.8,
6.8.2
brackets operator ([ ]), 6.5.2.1, 6.5.3.2
brackets punctuator ([ ]), 6.7.5.2, 6.7.8
branch cuts, 7.3.3
break statement, 6.8.6.3
broken-down time, 7.23.1, 7.23.2.3, 7.23.3,
7.23.3.1, 7.23.3.3, 7.23.3.4, 7.23.3.5
bsearch function, 7.20.5, 7.20.5.1
btowc function, 7.24.6.1.1
BUFSIZ macro, 7.19.1, 7.19.2, 7.19.5.5
byte, 3.6, 6.5.3.4
byte input/output functions, 7.19.1
byte-oriented stream, 7.19.2

call by value, 6.5.2.2
calloc function, 7.20.3, 7.20.3.1, 7.20.3.2,
7.20.3.4
carg functions, 7.3.9.1, G.6
carg type-generic macro, 7.22, G.7
carriage-return escape sequence (\r), 5.2.2,
6.4.4.4, 7.4.1.10
case label, 6.8.1, 6.8.4.2
case mapping functions
character, 7.4.2
wide character, 7.25.3.1
extensible, 7.25.3.2
casin functions, 7.3.5.2, G.6
type-generic macro for, 7.22
casinh functions, 7.3.6.2, G.6.2.2
type-generic macro for, 7.22
cast expression, 6.5.4
cast operator (( )), 6.5.4
catan functions, 7.3.5.3, G.6
type-generic macro for, 7.22
catanh functions, 7.3.6.3, G.6.2.3
type-generic macro for, 7.22
cbrt functions, 7.12.7.1, F.9.4.1
cbrt type-generic macro, 7.22
ccos functions, 7.3.5.4, G.6
type-generic macro for, 7.22
ccosh functions, 7.3.6.4, G.6.2.4
type-generic macro for, 7.22
ceil functions, 7.12.9.1, F.9.6.1
ceil type-generic macro, 7.22
cerf function, 7.26.1
cerfc function, 7.26.1
cexp functions, 7.3.7.1, G.6.3.1
type-generic macro for, 7.22
cexp2 function, 7.26.1
cexpm1 function, 7.26.1
char type, 6.2.5, 6.3.1.1, 6.7.2
char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
6.3.1.8
CHAR_BIT macro, 5.2.4.2.1
CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
CHAR_MIN macro, 5.2.4.2.1
character, 3.7, 3.7.1
character array initialization, 6.7.8
character case mapping functions, 7.4.2
wide character, 7.25.3.1
extensible, 7.25.3.2
character classification functions, 7.4.1
wide character, 7.25.2.1
extensible, 7.25.2.2
character constant, 5.1.1.2, 5.2.1, 6.4.4.4

C program, 5.1.1.1
C++, 7.8.1, 7.18.2, 7.18.3, 7.18.4
cabs functions, 7.3.8.1, G.6
type-generic macro for, 7.22
cacos functions, 7.3.5.1, G.6.1.1
type-generic macro for, 7.22
cacosh functions, 7.3.6.1, G.6.2.1
type-generic macro for, 7.22
calendar time, 7.23.1, 7.23.2.2, 7.23.2.3, 7.23.2.4,
7.23.3.2, 7.23.3.3, 7.23.3.4

522

WG14/N1256

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

complex.h header, 5.2.4.2.2, 7.3, 7.22, 7.26.1,
G.6, J.5.17
compliance, see conformancecomponents of time, 7.23.1
composite type, 6.2.7
compound assignment, 6.5.16.2
compound literals, 6.5.2.5
compound statement, 6.8.2
compound-literal operator (( ){ }), 6.5.2.5
concatenation functions
string, 7.21.3
wide string, 7.24.4.3
concatenation, preprocessing, see preprocessing
concatenation
conceptual models, 5.1
conditional inclusion, 6.10.1
conditional operator (? :), 6.5.15
conformance, 4conj functions, 7.3.9.3, G.6
conj type-generic macro, 7.22
const type qualifier, 6.7.3
const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
constant expression, 6.6, F.7.4
constants, 6.4.4
as primary expression, 6.5.1
character, 6.4.4.4
enumeration, 6.2.1, 6.4.4.3
floating, 6.4.4.2
hexadecimal, 6.4.4.1
integer, 6.4.4.1
octal, 6.4.4.1
constraint, 3.8, 4
content of structure/union/enumeration, 6.7.2.3
contiguity of allocated storage, 7.20.3
continue statement, 6.8.6.2
contracted expression, 6.5, 7.12.2, F.6
control character, 5.2.1, 7.4
control wide character, 7.25.2
conversion, 6.3
arithmetic operands, 6.3.1
array argument, 6.9.1
array parameter, 6.9.1
arrays, 6.3.2.1
boolean, 6.3.1.2
boolean, characters, and integers, 6.3.1.1
by assignment, 6.5.16.1
by return statement, 6.8.6.4
complex types, 6.3.1.6
explicit, 6.3
function, 6.3.2.1
function argument, 6.5.2.2, 6.9.1

character display semantics, 5.2.2
character handling header, 7.4, 7.11.1.1
character input/output functions, 7.19.7
wide character, 7.24.3
character sets, 5.2.1
character string literal, see string literalcharacter type conversion, 6.3.1.1
character types, 6.2.5, 6.7.8
cimag functions, 7.3.9.2, 7.3.9.4, G.6
cimag type-generic macro, 7.22, G.7
cis function, G.6
classification functions
character, 7.4.1
floating-point, 7.12.3
wide character, 7.25.2.1
extensible, 7.25.2.2
clearerr function, 7.19.10.1
clgamma function, 7.26.1
clock function, 7.23.2.1
clock_t type, 7.23.1, 7.23.2.1
CLOCKS_PER_SEC macro, 7.23.1, 7.23.2.1
clog functions, 7.3.7.2, G.6.3.2
type-generic macro for, 7.22
clog10 function, 7.26.1
clog1p function, 7.26.1
clog2 function, 7.26.1
collating sequences, 5.2.1
colon punctuator (:), 6.7.2.1
comma operator (,), 6.5.17
comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,
6.7.2.3, 6.7.8
command processor, 7.20.4.6
comment delimiters (/* */ and //), 6.4.9
comments, 5.1.1.2, 6.4, 6.4.9
common extensions, J.5
common initial sequence, 6.5.2.3
common real type, 6.3.1.8
common warnings, I
comparison functions, 7.20.5, 7.20.5.1, 7.20.5.2
string, 7.21.4
wide string, 7.24.4.4
comparison macros, 7.12.14
comparison, pointer, 6.5.8
compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.5
compl macro, 7.9
complement operator (~), 6.5.3.3
complex macro, 7.3.1
complex numbers, 6.2.5, G
complex type conversion, 6.3.1.6, 6.3.1.7
complex type domain, 6.2.5
complex types, 6.2.5, 6.7.2, G

Index

523

∗

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

function designators, 6.3.2.1
function parameter, 6.9.1
imaginary, G.4.1
imaginary and complex, G.4.3
implicit, 6.3
lvalues, 6.3.2.1
pointer, 6.3.2.1, 6.3.2.3
real and complex, 6.3.1.7
real and imaginary, G.4.2
real floating and integer, 6.3.1.4, F.3, F.4
real floating types, 6.3.1.5, F.3
signed and unsigned integers, 6.3.1.3
usual arithmetic, see usual arithmetic
conversions
void type, 6.3.2.2
conversion functions
multibyte/wide character, 7.20.7
extended, 7.24.6
restartable, 7.24.6.3
multibyte/wide string, 7.20.8
restartable, 7.24.6.4
numeric, 7.8.2.3, 7.20.1
wide string, 7.8.2.4, 7.24.4.1
single byte/wide character, 7.24.6.1
time, 7.23.3
wide character, 7.24.5
conversion specifier, 7.19.6.1, 7.19.6.2, 7.24.2.1,
7.24.2.2
conversion state, 7.20.7, 7.24.6, 7.24.6.2.1,
7.24.6.3, 7.24.6.3.2, 7.24.6.3.3, 7.24.6.4,
7.24.6.4.1, 7.24.6.4.2
conversion state functions, 7.24.6.2
copying functions
string, 7.21.2
wide string, 7.24.4.2
copysign functions, 7.3.9.4, 7.12.11.1, F.3,
F.9.8.1
copysign type-generic macro, 7.22
correctly rounded result, 3.9
corresponding real type, 6.2.5
cos functions, 7.12.4.5, F.9.1.5
cos type-generic macro, 7.22, G.7
cosh functions, 7.12.5.4, F.9.2.4
cosh type-generic macro, 7.22, G.7
cpow functions, 7.3.8.2, G.6.4.1
type-generic macro for, 7.22
cproj functions, 7.3.9.4, G.6
cproj type-generic macro, 7.22
creal functions, 7.3.9.5, G.6
creal type-generic macro, 7.22, G.7
csin functions, 7.3.5.5, G.6

524

WG14/N1256

type-generic macro for, 7.22
csinh functions, 7.3.6.5, G.6.2.5
type-generic macro for, 7.22
csqrt functions, 7.3.8.3, G.6.4.2
type-generic macro for, 7.22
ctan functions, 7.3.5.6, G.6
type-generic macro for, 7.22
ctanh functions, 7.3.6.6, G.6.2.6
type-generic macro for, 7.22
ctgamma function, 7.26.1
ctime function, 7.23.3.2
ctype.h header, 7.4, 7.26.2
current object, 6.7.8
CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4
data stream, see streams
date and time header, 7.23
Daylight Saving Time, 7.23.1
DBL_DIG macro, 5.2.4.2.2
DBL_EPSILON macro, 5.2.4.2.2
DBL_MANT_DIG macro, 5.2.4.2.2
DBL_MAX macro, 5.2.4.2.2
DBL_MAX_10_EXP macro, 5.2.4.2.2
DBL_MAX_EXP macro, 5.2.4.2.2
DBL_MIN macro, 5.2.4.2.2
DBL_MIN_10_EXP macro, 5.2.4.2.2
DBL_MIN_EXP macro, 5.2.4.2.2
decimal constant, 6.4.4.1
decimal digit, 5.2.1
decimal-point character, 7.1.1, 7.11.2.1
DECIMAL_DIG macro, 5.2.4.2.2, 7.19.6.1,
7.20.1.3, 7.24.2.1, 7.24.4.1.1, F.5
declaration specifiers, 6.7
declarations, 6.7
function, 6.7.5.3
pointer, 6.7.5.1
structure/union, 6.7.2.1
typedef, 6.7.7
declarator, 6.7.5
abstract, 6.7.6
declarator type derivation, 6.2.5, 6.7.5
decrement operators, see arithmetic operators,
increment and decrement
default argument promotions, 6.5.2.2
default initialization, 6.7.8
default label, 6.8.1, 6.8.4.2
define preprocessing directive, 6.10.3
defined operator, 6.10.1, 6.10.8
definition, 6.7
function, 6.9.1
derived declarator types, 6.2.5

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

end-of-file indicator, 7.19.1, 7.19.5.3, 7.19.7.1,
7.19.7.5, 7.19.7.6, 7.19.7.11, 7.19.9.2,
7.19.9.3, 7.19.10.1, 7.19.10.2, 7.24.3.1,
7.24.3.10
end-of-file macro, see EOF macro
end-of-line indicator, 5.2.1
endif preprocessing directive, 6.10.1
enum type, 6.2.5, 6.7.2, 6.7.2.2
enumerated type, 6.2.5
enumeration, 6.2.5, 6.7.2.2
enumeration constant, 6.2.1, 6.4.4.3
enumeration content, 6.7.2.3
enumeration members, 6.7.2.2
enumeration specifiers, 6.7.2.2
enumeration tag, 6.2.3, 6.7.2.3
enumerator, 6.7.2.2
environment, 5environment functions, 7.20.4
environment list, 7.20.4.5
environmental considerations, 5.2
environmental limits, 5.2.4, 7.13.1.1, 7.19.2,
7.19.3, 7.19.4.4, 7.19.6.1, 7.20.2.1, 7.20.4.2,
7.24.2.1
EOF macro, 7.4, 7.19.1, 7.19.5.1, 7.19.5.2,
7.19.6.2, 7.19.6.7, 7.19.6.9, 7.19.6.11,
7.19.6.14, 7.19.7.1, 7.19.7.3, 7.19.7.4,
7.19.7.5, 7.19.7.6, 7.19.7.9, 7.19.7.10,
7.19.7.11, 7.24.1, 7.24.2.2, 7.24.2.4,
7.24.2.6, 7.24.2.8, 7.24.2.10, 7.24.2.12,
7.24.3.4, 7.24.6.1.1, 7.24.6.1.2
equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.8
equal-to operator, see equality operator
equality expressions, 6.5.9
equality operator (==), 6.5.9
ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1,
7.20.1.3, 7.20.1.4, 7.24.4.1.1, 7.24.4.1.2, seealso range error
erf functions, 7.12.8.1, F.9.5.1
erf type-generic macro, 7.22
erfc functions, 7.12.8.2, F.9.5.2
erfc type-generic macro, 7.22
errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4,
7.12.1, 7.14.1.1, 7.19.3, 7.19.9.3, 7.19.10.4,
7.20.1, 7.20.1.3, 7.20.1.4, 7.21.6.2, 7.24.3.1,
7.24.3.3, 7.24.4.1.1, 7.24.4.1.2, 7.24.6.3.2,
7.24.6.3.3, 7.24.6.4.1, 7.24.6.4.2, J.5.17
errno.h header, 7.5, 7.26.3
error
domain, see domain error
encoding, see encoding error
range, see range error

derived types, 6.2.5
designated initializer, 6.7.8
destringizing, 6.10.9
device input/output, 5.1.2.3
diagnostic message, 3.10, 5.1.1.3
diagnostics, 5.1.1.3
diagnostics header, 7.2
difftime function, 7.23.2.2
digit, 5.2.1, 7.4
digraphs, 6.4.6
direct input/output functions, 7.19.8
display device, 5.2.2
div function, 7.20.6.2
div_t type, 7.20
division assignment operator (/=), 6.5.16.2
division operator (/), 6.5.5, F.3, G.5.1
do statement, 6.8.5.2
documentation of implementation, 4domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4,
7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7,
7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11,
7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5,
7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3
dot operator (.), 6.5.2.3
double _Complex type, 6.2.5
double _Complex type conversion, 6.3.1.6,
6.3.1.7, 6.3.1.8
double _Imaginary type, G.2
double type, 6.2.5, 6.4.4.2, 6.7.2, 7.19.6.2,
7.24.2.2, F.2
double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
6.3.1.8
double-precision arithmetic, 5.1.2.3
double-quote escape sequence (\"), 6.4.4.4,
6.4.5, 6.10.9
double_t type, 7.12, J.5.6

EDOM macro, 7.5, 7.12.1, see also domain error
effective type, 6.5
EILSEQ macro, 7.5, 7.19.3, 7.24.3.1, 7.24.3.3,
7.24.6.3.2, 7.24.6.3.3, 7.24.6.4.1, 7.24.6.4.2,
see also encoding error
element type, 6.2.5
elif preprocessing directive, 6.10.1
ellipsis punctuator (...), 6.5.2.2, 6.7.5.3, 6.10.3
else preprocessing directive, 6.10.1
else statement, 6.8.4.1
empty statement, 6.8.3
encoding error, 7.19.3, 7.24.3.1, 7.24.3.3,
7.24.6.3.2, 7.24.6.3.3, 7.24.6.4.1, 7.24.6.4.2
end-of-file, 7.24.1

Index

525

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

extended characters, 5.2.1
extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1,
7.18
extended multibyte/wide character conversion
utilities, 7.24.6
extensible wide character case mapping functions,7.25.3.2
extensible wide character classification functions,7.25.2.2
extern storage-class specifier, 6.2.2, 6.7.1
external definition, 6.9
external identifiers, underscore, 7.1.3
external linkage, 6.2.2
external name, 6.4.2.1
external object definitions, 6.9.2

error conditions, 7.12.1
error functions, 7.12.8, F.9.5
error indicator, 7.19.1, 7.19.5.3, 7.19.7.1,
7.19.7.3, 7.19.7.5, 7.19.7.6, 7.19.7.8,
7.19.7.9, 7.19.9.2, 7.19.10.1, 7.19.10.3,
7.24.3.1, 7.24.3.3
error preprocessing directive, 4, 6.10.5
error-handling functions, 7.19.10, 7.21.6.2
escape character (\), 6.4.4.4
escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4
evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12
evaluation method, 5.2.4.2.2, 6.5, F.7.5
evaluation order, 6.5
exceptional condition, 6.5, 7.12.1
excess precision, 5.2.4.2.2, 6.3.1.5, 6.3.1.8,
6.8.6.4
excess range, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, 6.8.6.4
exclusive OR operators
bitwise (^), 6.5.11
bitwise assignment (^=), 6.5.16.2
executable program, 5.1.1.1
execution character set, 5.2.1
execution environment, 5, 5.1.2, see also
environmental limits
execution sequence, 5.1.2.3, 6.8
exit function, 5.1.2.2.3, 7.19.3, 7.20, 7.20.4.3,
7.20.4.4
EXIT_FAILURE macro, 7.20, 7.20.4.3
EXIT_SUCCESS macro, 7.20, 7.20.4.3
exp functions, 7.12.6.1, F.9.3.1
exp type-generic macro, 7.22
exp2 functions, 7.12.6.2, F.9.3.2
exp2 type-generic macro, 7.22
explicit conversion, 6.3
expm1 functions, 7.12.6.3, F.9.3.3
expm1 type-generic macro, 7.22
exponent part, 6.4.4.2
exponential functions
complex, 7.3.7, G.6.3
real, 7.12.6, F.9.3
expression, 6.5
assignment, 6.5.16
cast, 6.5.4
constant, 6.6
full, 6.8
order of evaluation, 6.5
parenthesized, 6.5.1
primary, 6.5.1
unary, 6.5.3
expression statement, 6.8.3
extended character set, 3.7.2, 5.2.1, 5.2.1.2

526

WG14/N1256

fabs functions, 7.12.7.2, F.9.4.2
fabs type-generic macro, 7.22, G.7
false macro, 7.16
fclose function, 7.19.5.1
fdim functions, 7.12.12.1, F.9.9.1
fdim type-generic macro, 7.22
FE_ALL_EXCEPT macro, 7.6
FE_DFL_ENV macro, 7.6
FE_DIVBYZERO macro, 7.6, 7.12, F.3
FE_DOWNWARD macro, 7.6, F.3
FE_INEXACT macro, 7.6, F.3
FE_INVALID macro, 7.6, 7.12, F.3
FE_OVERFLOW macro, 7.6, 7.12, F.3
FE_TONEAREST macro, 7.6, F.3
FE_TOWARDZERO macro, 7.6, F.3
FE_UNDERFLOW macro, 7.6, F.3
FE_UPWARD macro, 7.6, F.3
feclearexcept function, 7.6.2, 7.6.2.1, F.3
fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3
fegetexceptflag function, 7.6.2, 7.6.2.2, F.3
fegetround function, 7.6, 7.6.3.1, F.3
feholdexcept function, 7.6.4.2, 7.6.4.3,
7.6.4.4, F.3
fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H
FENV_ACCESS pragma, 6.10.6, 7.6.1, F.7, F.8,
F.9
fenv_t type, 7.6
feof function, 7.19.10.2
feraiseexcept function, 7.6.2, 7.6.2.3, F.3
ferror function, 7.19.10.3
fesetenv function, 7.6.4.3, F.3
fesetexceptflag function, 7.6.2, 7.6.2.4, F.3
fesetround function, 7.6, 7.6.3.2, F.3
fetestexcept function, 7.6.2, 7.6.2.5, F.3
feupdateenv function, 7.6.4.2, 7.6.4.4, F.3

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

floating-point status flag, 7.6, F.7.6
floor functions, 7.12.9.2, F.9.6.2
floor type-generic macro, 7.22
FLT_DIG macro, 5.2.4.2.2
FLT_EPSILON macro, 5.2.4.2.2
FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.8.6.4,
7.12
FLT_MANT_DIG macro, 5.2.4.2.2
FLT_MAX macro, 5.2.4.2.2
FLT_MAX_10_EXP macro, 5.2.4.2.2
FLT_MAX_EXP macro, 5.2.4.2.2
FLT_MIN macro, 5.2.4.2.2
FLT_MIN_10_EXP macro, 5.2.4.2.2
FLT_MIN_EXP macro, 5.2.4.2.2
FLT_RADIX macro, 5.2.4.2.2, 7.19.6.1, 7.20.1.3,
7.24.2.1, 7.24.4.1.1
FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3
fma functions, 7.12, 7.12.13.1, F.9.10.1
fma type-generic macro, 7.22
fmax functions, 7.12.12.2, F.9.9.2
fmax type-generic macro, 7.22
fmin functions, 7.12.12.3, F.9.9.3
fmin type-generic macro, 7.22
fmod functions, 7.12.10.1, F.9.7.1
fmod type-generic macro, 7.22
fopen function, 7.19.5.3, 7.19.5.4
FOPEN_MAX macro, 7.19.1, 7.19.3, 7.19.4.3
for statement, 6.8.5, 6.8.5.3
form-feed character, 5.2.1, 6.4
form-feed escape sequence (\f), 5.2.2, 6.4.4.4,
7.4.1.10
formal argument (deprecated), 3.15
formal parameter, 3.15
formatted input/output functions, 7.11.1.1, 7.19.6
wide character, 7.24.2
fortran keyword, J.5.9
forward reference, 3.11
FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, seealso contracted expression
FP_FAST_FMA macro, 7.12
FP_FAST_FMAF macro, 7.12
FP_FAST_FMAL macro, 7.12
FP_ILOGB0 macro, 7.12, 7.12.6.5
FP_ILOGBNAN macro, 7.12, 7.12.6.5
FP_INFINITE macro, 7.12, F.3
FP_NAN macro, 7.12, F.3
FP_NORMAL macro, 7.12, F.3
FP_SUBNORMAL macro, 7.12, F.3
FP_ZERO macro, 7.12, F.3
fpclassify macro, 7.12.3.1, F.3
fpos_t type, 7.19.1, 7.19.2

fexcept_t type, 7.6, F.3
fflush function, 7.19.5.2, 7.19.5.3
fgetc function, 7.19.1, 7.19.3, 7.19.7.1,
7.19.7.5, 7.19.8.1
fgetpos function, 7.19.2, 7.19.9.1, 7.19.9.3
fgets function, 7.19.1, 7.19.7.2
fgetwc function, 7.19.1, 7.19.3, 7.24.3.1,
7.24.3.6
fgetws function, 7.19.1, 7.24.3.2
field width, 7.19.6.1, 7.24.2.1
file, 7.19.3
access functions, 7.19.5
name, 7.19.3
operations, 7.19.4
position indicator, 7.19.1, 7.19.2, 7.19.3,
7.19.5.3, 7.19.7.1, 7.19.7.3, 7.19.7.11,
7.19.8.1, 7.19.8.2, 7.19.9.1, 7.19.9.2,
7.19.9.3, 7.19.9.4, 7.19.9.5, 7.24.3.1,
7.24.3.3, 7.24.3.10
positioning functions, 7.19.9
file scope, 6.2.1, 6.9
FILE type, 7.19.1, 7.19.3
FILENAME_MAX macro, 7.19.1
flags, 7.19.6.1, 7.24.2.1
floating-point status, see floating-point statusflag
flexible array member, 6.7.2.1
float _Complex type, 6.2.5
float _Complex type conversion, 6.3.1.6,
6.3.1.7, 6.3.1.8
float _Imaginary type, G.2
float type, 6.2.5, 6.4.4.2, 6.7.2, F.2
float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
6.3.1.8
float.h header, 4, 5.2.4.2.2, 7.7, 7.20.1.3,
7.24.4.1.1
float_t type, 7.12, J.5.6
floating constant, 6.4.4.2
floating suffix, f or F, 6.4.4.2
floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
F.3, F.4
floating types, 6.2.5, 6.11.1
floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5,
7.20.1.3, F.5, see also contracted expression
floating-point arithmetic functions, 7.12, F.9
floating-point classification functions, 7.12.3
floating-point control mode, 7.6, F.7.6
floating-point environment, 7.6, F.7, F.7.6
floating-point exception, 7.6, 7.6.2, F.9
floating-point number, 5.2.4.2.2, 6.2.5
floating-point rounding mode, 5.2.4.2.2

Index

527

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

language, 6.11
library, 7.26
fwide function, 7.19.2, 7.24.3.5
fwprintf function, 7.8.1, 7.19.1, 7.19.6.2,
7.24.2.1, 7.24.2.2, 7.24.2.3, 7.24.2.5,
7.24.2.11
fwrite function, 7.19.1, 7.19.8.2
fwscanf function, 7.8.1, 7.19.1, 7.24.2.2,
7.24.2.4, 7.24.2.6, 7.24.2.12, 7.24.3.10

fprintf function, 7.8.1, 7.19.1, 7.19.6.1,
7.19.6.2, 7.19.6.3, 7.19.6.5, 7.19.6.6,
7.19.6.8, 7.24.2.2, F.3
fputc function, 5.2.2, 7.19.1, 7.19.3, 7.19.7.3,
7.19.7.8, 7.19.8.2
fputs function, 7.19.1, 7.19.7.4
fputwc function, 7.19.1, 7.19.3, 7.24.3.3,
7.24.3.8
fputws function, 7.19.1, 7.24.3.4
fread function, 7.19.1, 7.19.8.1
free function, 7.20.3.2, 7.20.3.4
freestanding execution environment, 4, 5.1.2,
5.1.2.1
freopen function, 7.19.2, 7.19.5.4
frexp functions, 7.12.6.4, F.9.3.4
frexp type-generic macro, 7.22
fscanf function, 7.8.1, 7.19.1, 7.19.6.2,
7.19.6.4, 7.19.6.7, 7.19.6.9, F.3
fseek function, 7.19.1, 7.19.5.3, 7.19.7.11,
7.19.9.2, 7.19.9.4, 7.19.9.5, 7.24.3.10
fsetpos function, 7.19.2, 7.19.5.3, 7.19.7.11,
7.19.9.1, 7.19.9.3, 7.24.3.10
ftell function, 7.19.9.2, 7.19.9.4
full declarator, 6.7.5
full expression, 6.8
fully buffered stream, 7.19.3
functionargument, 6.5.2.2, 6.9.1
body, 6.9.1
call, 6.5.2.2
library, 7.1.4
declarator, 6.7.5.3, 6.11.6
definition, 6.7.5.3, 6.9.1, 6.11.7
designator, 6.3.2.1
image, 5.2.3
library, 5.1.1.1, 7.1.4
name length, 5.2.4.1, 6.4.2.1, 6.11.3
parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1
prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7,
6.7.5.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12
prototype scope, 6.2.1, 6.7.5.2
recursive call, 6.5.2.2
return, 6.8.6.4
scope, 6.2.1
type, 6.2.5
type conversion, 6.3.2.1
function specifiers, 6.7.4
function type, 6.2.5
function-call operator (( )), 6.5.2.2
function-like macro, 6.10.3
future directions

528

WG14/N1256

gamma functions, 7.12.8, F.9.5
general utilities, 7.20
wide string, 7.24.4
general wide string utilities, 7.24.4
generic parameters, 7.22
getc function, 7.19.1, 7.19.7.5, 7.19.7.6
getchar function, 7.19.1, 7.19.7.6
getenv function, 7.20.4.5
gets function, 7.19.1, 7.19.7.7, 7.26.9
getwc function, 7.19.1, 7.24.3.6, 7.24.3.7
getwchar function, 7.19.1, 7.24.3.7
gmtime function, 7.23.3.3
goto statement, 6.2.1, 6.8.1, 6.8.6.1
graphic characters, 5.2.1
greater-than operator (>), 6.5.8
greater-than-or-equal-to operator (>=), 6.5.8

header, 5.1.1.1, 7.1.2, see also standard headersheader names, 6.4, 6.4.7, 6.10.2
hexadecimal constant, 6.4.4.1
hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4
hexadecimal prefix, 6.4.4.1
hexadecimal-character escape sequence(\x hexadecimal digits), 6.4.4.4
high-order bit, 3.6
horizontal-tab character, 5.2.1, 6.4
horizontal-tab escape sequence (\r), 7.25.2.1.3
horizontal-tab escape sequence (\t), 5.2.2,
6.4.4.4, 7.4.1.3, 7.4.1.10
hosted execution environment, 4, 5.1.2, 5.1.2.2
HUGE_VAL macro, 7.12, 7.12.1, 7.20.1.3,
7.24.4.1.1, F.9
HUGE_VALF macro, 7.12, 7.12.1, 7.20.1.3,
7.24.4.1.1, F.9
HUGE_VALL macro, 7.12, 7.12.1, 7.20.1.3,
7.24.4.1.1, F.9
hyperbolic functions
complex, 7.3.6, G.6.2
real, 7.12.5, F.9.2
hypot functions, 7.12.7.3, F.9.4.3
hypot type-generic macro, 7.22

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

initial position, 5.2.2
initial shift state, 5.2.1.2
initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.8,
F.7.5
in blocks, 6.8
initializer, 6.7.8
permitted form, 6.6
string literal, 6.3.2.1
inline, 6.7.4
inner scope, 6.2.1
input failure, 7.24.2.6, 7.24.2.8, 7.24.2.10
input/output functions
character, 7.19.7
direct, 7.19.8
formatted, 7.19.6
wide character, 7.24.2
wide character, 7.24.3
formatted, 7.24.2
input/output header, 7.19
input/output, device, 5.1.2.3
int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2
int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
6.3.1.8
INT_FASTN_MAX macros, 7.18.2.3
INT_FASTN_MIN macros, 7.18.2.3
int_fastN_t types, 7.18.1.3
INT_LEASTN_MAX macros, 7.18.2.2
INT_LEASTN_MIN macros, 7.18.2.2
int_leastN_t types, 7.18.1.2
INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5
INT_MIN macro, 5.2.4.2.1, 7.12
integer arithmetic functions, 7.8.2.1, 7.8.2.2,
7.20.6integer character constant, 6.4.4.4
integer constant, 6.4.4.1
integer constant expression, 6.6
integer conversion rank, 6.3.1.1
integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1,
6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.18.2, 7.18.3,
7.19.6.1, 7.24.2.1
integer suffix, 6.4.4.1
integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
F.3, F.4
integer types, 6.2.5, 7.18
extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.18
interactive device, 5.1.2.3, 7.19.3, 7.19.5.3
internal linkage, 6.2.2
internal name, 6.4.2.1
interrupt, 5.2.3
INTMAX_C macro, 7.18.4.2
INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.18.2.5

I macro, 7.3.1, 7.3.9.4, G.6
identifier, 6.4.2.1, 6.5.1
linkage, see linkage
maximum length, 6.4.2.1
name spaces, 6.2.3
reserved, 6.4.1, 7.1.3
scope, 6.2.1
type, 6.2.5
identifier list, 6.7.5
identifier nondigit, 6.4.2.1
IEC 559, F.1
IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8, 7.3.3, 7.6,
7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G, H.1
IEEE 754, F.1
IEEE 854, F.1
IEEE floating-point arithmetic standard, see
IEC 60559, ANSI/IEEE 754,
ANSI/IEEE 854
if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,
6.10.1, 7.1.4
if statement, 6.8.4.1
ifdef preprocessing directive, 6.10.1
ifndef preprocessing directive, 6.10.1
ilogb functions, 7.12, 7.12.6.5, F.9.3.5
ilogb type-generic macro, 7.22
imaginary macro, 7.3.1, G.6
imaginary numbers, G
imaginary type domain, G.2
imaginary types, G
imaxabs function, 7.8.2.1
imaxdiv function, 7.8, 7.8.2.2
imaxdiv_t type, 7.8
implementation, 3.12
implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1,
6.7.5, 6.8.4.2, E, see also environmental
limitsimplementation-defined behavior, 3.4.1, 4, J.3
implementation-defined value, 3.17.1
implicit conversion, 6.3
implicit initialization, 6.7.8
include preprocessing directive, 5.1.1.2, 6.10.2
inclusive OR operators
bitwise (|), 6.5.12
bitwise assignment (|=), 6.5.16.2
incomplete type, 6.2.5
increment operators, see arithmetic operators,
increment and decrement
indeterminate value, 3.17.2
indirection operator (*), 6.5.2.1, 6.5.3.2
inequality operator (!=), 6.5.9
INFINITY macro, 7.3.9.4, 7.12, F.2.1

Index

529

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.18.2.5
intmax_t type, 7.18.1.5, 7.19.6.1, 7.19.6.2,
7.24.2.1, 7.24.2.2
INTN_C macros, 7.18.4.1
INTN_MAX macros, 7.18.2.1
INTN_MIN macros, 7.18.2.1
intN_t types, 7.18.1.1
INTPTR_MAX macro, 7.18.2.4
INTPTR_MIN macro, 7.18.2.4
intptr_t type, 7.18.1.4
inttypes.h header, 7.8, 7.26.4
isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10
isalpha function, 7.4.1.1, 7.4.1.2
isblank function, 7.4.1.3
iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7,
7.4.1.11
isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5,
7.4.1.7, 7.4.1.11, 7.11.1.1
isfinite macro, 7.12.3.2, F.3
isgraph function, 7.4.1.6
isgreater macro, 7.12.14.1, F.3
isgreaterequal macro, 7.12.14.2, F.3
isinf macro, 7.12.3.3
isless macro, 7.12.14.3, F.3
islessequal macro, 7.12.14.4, F.3
islessgreater macro, 7.12.14.5, F.3
islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1,
7.4.2.2
isnan macro, 7.12.3.4, F.3
isnormal macro, 7.12.3.5
ISO 31−11, 2, 3
ISO 4217, 2, 7.11.2.1
ISO 8601, 2, 7.23.3.5
ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8
ISO/IEC 10976−1, H.1
ISO/IEC 2382−1, 2, 3
ISO/IEC 646, 2, 5.2.1.1
ISO/IEC 9945−2, 7.11
ISO/IEC TR 10176, D
iso646.h header, 4, 7.9
isprint function, 5.2.2, 7.4.1.8
ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
7.4.1.11
isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
7.4.1.10, 7.4.1.11, 7.19.6.2, 7.20.1.3,
7.20.1.4, 7.24.2.2
isunordered macro, 7.12.14.6, F.3
isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1,
7.4.2.2
iswalnum function, 7.25.2.1.1, 7.25.2.1.9,
7.25.2.1.10, 7.25.2.2.1

530

WG14/N1256

iswalpha function, 7.25.2.1.1, 7.25.2.1.2,
7.25.2.2.1
iswblank function, 7.25.2.1.3, 7.25.2.2.1
iswcntrl function, 7.25.2.1.2, 7.25.2.1.4,
7.25.2.1.7, 7.25.2.1.11, 7.25.2.2.1
iswctype function, 7.25.2.2.1, 7.25.2.2.2
iswdigit function, 7.25.2.1.1, 7.25.2.1.2,
7.25.2.1.5, 7.25.2.1.7, 7.25.2.1.11, 7.25.2.2.1
iswgraph function, 7.25.2.1, 7.25.2.1.6,
7.25.2.1.10, 7.25.2.2.1
iswlower function, 7.25.2.1.2, 7.25.2.1.7,
7.25.2.2.1, 7.25.3.1.1, 7.25.3.1.2
iswprint function, 7.25.2.1.6, 7.25.2.1.8,
7.25.2.2.1
iswpunct function, 7.25.2.1, 7.25.2.1.2,
7.25.2.1.7, 7.25.2.1.9, 7.25.2.1.10,
7.25.2.1.11, 7.25.2.2.1
iswspace function, 7.19.6.2, 7.24.2.2,
7.24.4.1.1, 7.24.4.1.2, 7.25.2.1.2, 7.25.2.1.6,
7.25.2.1.7, 7.25.2.1.9, 7.25.2.1.10,
7.25.2.1.11, 7.25.2.2.1
iswupper function, 7.25.2.1.2, 7.25.2.1.11,
7.25.2.2.1, 7.25.3.1.1, 7.25.3.1.2
iswxdigit function, 7.25.2.1.12, 7.25.2.2.1
isxdigit function, 7.4.1.12, 7.11.1.1
italic type convention, 3, 6.1
iteration statements, 6.8.5
jmp_buf type, 7.13
jump statements, 6.8.6
keywords, 6.4.1, G.2, J.5.9, J.5.10
known constant size, 6.2.5

L_tmpnam macro, 7.19.1, 7.19.4.4
label name, 6.2.1, 6.2.3
labeled statement, 6.8.1
labs function, 7.20.6.1
language, 6
future directions, 6.11
syntax summary, A
Latin alphabet, 5.2.1, 6.4.2.1
LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1
LC_COLLATE macro, 7.11, 7.11.1.1, 7.21.4.3,
7.24.4.4.2
LC_CTYPE macro, 7.11, 7.11.1.1, 7.20, 7.20.7,
7.20.8, 7.24.6, 7.25.1, 7.25.2.2.1, 7.25.2.2.2,
7.25.3.2.1, 7.25.3.2.2
LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
LC_TIME macro, 7.11, 7.11.1.1, 7.23.3.5

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

lconv structure type, 7.11
LDBL_DIG macro, 5.2.4.2.2
LDBL_EPSILON macro, 5.2.4.2.2
LDBL_MANT_DIG macro, 5.2.4.2.2
LDBL_MAX macro, 5.2.4.2.2
LDBL_MAX_10_EXP macro, 5.2.4.2.2
LDBL_MAX_EXP macro, 5.2.4.2.2
LDBL_MIN macro, 5.2.4.2.2
LDBL_MIN_10_EXP macro, 5.2.4.2.2
LDBL_MIN_EXP macro, 5.2.4.2.2
ldexp functions, 7.12.6.6, F.9.3.6
ldexp type-generic macro, 7.22
ldiv function, 7.20.6.2
ldiv_t type, 7.20
leading underscore in identifiers, 7.1.3
left-shift assignment operator (<<=), 6.5.16.2
left-shift operator (<<), 6.5.7
lengthexternal name, 5.2.4.1, 6.4.2.1, 6.11.3
function name, 5.2.4.1, 6.4.2.1, 6.11.3
identifier, 6.4.2.1
internal name, 5.2.4.1, 6.4.2.1
length function, 7.20.7.1, 7.21.6.3, 7.24.4.6.1,
7.24.6.3.1
length modifier, 7.19.6.1, 7.19.6.2, 7.24.2.1,
7.24.2.2
less-than operator (<), 6.5.8
less-than-or-equal-to operator (<=), 6.5.8
letter, 5.2.1, 7.4
lexical elements, 5.1.1.2, 6.4
lgamma functions, 7.12.8.3, F.9.5.3
lgamma type-generic macro, 7.22
library, 5.1.1.1, 7
future directions, 7.26
summary, B
terms, 7.1.1
use of functions, 7.1.4
lifetime, 6.2.4
limitsenvironmental, see environmental limits
implementation, see implementation limits
numerical, see numerical limits
translation, see translation limits
limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10
line buffered stream, 7.19.3
line number, 6.10.4, 6.10.8
line preprocessing directive, 6.10.4
lines, 5.1.1.2, 7.19.2
preprocessing directive, 6.10
linkage, 6.2.2, 6.7, 6.7.4, 6.7.5.2, 6.9, 6.9.2,
6.11.2

ISO/IEC 9899:TC3

llabs function, 7.20.6.1
lldiv function, 7.20.6.2
lldiv_t type, 7.20
LLONG_MAX macro, 5.2.4.2.1, 7.20.1.4,
7.24.4.1.2
LLONG_MIN macro, 5.2.4.2.1, 7.20.1.4,
7.24.4.1.2
llrint functions, 7.12.9.5, F.3, F.9.6.5
llrint type-generic macro, 7.22
llround functions, 7.12.9.7, F.9.6.7
llround type-generic macro, 7.22
local time, 7.23.1
locale, 3.4.2
locale-specific behavior, 3.4.2, J.4
locale.h header, 7.11, 7.26.5
localeconv function, 7.11.1.1, 7.11.2.1
localization, 7.11
localtime function, 7.23.3.4
log functions, 7.12.6.7, F.9.3.7
log type-generic macro, 7.22
log10 functions, 7.12.6.8, F.9.3.8
log10 type-generic macro, 7.22
log1p functions, 7.12.6.9, F.9.3.9
log1p type-generic macro, 7.22
log2 functions, 7.12.6.10, F.9.3.10
log2 type-generic macro, 7.22
logarithmic functions
complex, 7.3.7, G.6.3
real, 7.12.6, F.9.3
logb functions, 7.12.6.11, F.3, F.9.3.11
logb type-generic macro, 7.22
logical operators
AND (&&), 6.5.13
negation (!), 6.5.3.3
OR (||), 6.5.14
logical source lines, 5.1.1.2
long double _Complex type, 6.2.5
long double _Complex type conversion,
6.3.1.6, 6.3.1.7, 6.3.1.8
long double _Imaginary type, G.2
long double suffix, l or L, 6.4.4.2
long double type, 6.2.5, 6.4.4.2, 6.7.2,
7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2, F.2
long double type conversion, 6.3.1.4, 6.3.1.5,
6.3.1.7, 6.3.1.8
long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2
long int type conversion, 6.3.1.1, 6.3.1.3,
6.3.1.4, 6.3.1.8
long integer suffix, l or L, 6.4.4.1
long long int type, 6.2.5, 6.3.1.1, 6.7.2,

Index

531

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2
long long int type conversion, 6.3.1.1,
6.3.1.3, 6.3.1.4, 6.3.1.8
long long integer suffix, ll or LL, 6.4.4.1
LONG_MAX macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2
LONG_MIN macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2
longjmp function, 7.13.1.1, 7.13.2.1, 7.20.4.3
loop body, 6.8.5
low-order bit, 3.6
lowercase letter, 5.2.1
lrint functions, 7.12.9.5, F.3, F.9.6.5
lrint type-generic macro, 7.22
lround functions, 7.12.9.7, F.9.6.7
lround type-generic macro, 7.22
lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16

mbsinit function, 7.24.6.2.1
mbsrtowcs function, 7.24.6.4.1
mbstate_t type, 7.19.2, 7.19.3, 7.19.6.1,
7.19.6.2, 7.24.1, 7.24.2.1, 7.24.2.2, 7.24.6,
7.24.6.2.1, 7.24.6.3, 7.24.6.3.1, 7.24.6.4
mbstowcs function, 6.4.5, 7.20.8.1, 7.24.6.4
mbtowc function, 7.20.7.1, 7.20.7.2, 7.20.8.1,
7.24.6.3
member access operators (. and ->), 6.5.2.3
member alignment, 6.7.2.1
memchr function, 7.21.5.1
memcmp function, 7.21.4, 7.21.4.1
memcpy function, 7.21.2.1
memmove function, 7.21.2.2
memory management functions, 7.20.3
memset function, 7.21.6.1
minimum functions, 7.12.12, F.9.9
minus operator, unary, 6.5.3.3
miscellaneous functions
string, 7.21.6
wide string, 7.24.4.6
mktime function, 7.23.2.3
modf functions, 7.12.6.12, F.9.3.12
modifiable lvalue, 6.3.2.1
modulus functions, 7.12.6.12
modulus, complex, 7.3.8.1
multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4
multibyte conversion functions
wide character, 7.20.7
extended, 7.24.6
restartable, 7.24.6.3
wide string, 7.20.8
restartable, 7.24.6.4
multibyte string, 7.1.1
multibyte/wide character conversion functions,7.20.7extended, 7.24.6
restartable, 7.24.6.3
multibyte/wide string conversion functions, 7.20.8
restartable, 7.24.6.4
multidimensional array, 6.5.2.1
multiplication assignment operator (*=), 6.5.16.2
multiplication operator (*), 6.5.5, F.3, G.5.1
multiplicative expressions, 6.5.5, G.5.1

macro argument substitution, 6.10.3.1
macro definition
library function, 7.1.4
macro invocation, 6.10.3
macro name, 6.10.3
length, 5.2.4.1
predefined, 6.10.8, 6.11.9
redefinition, 6.10.3
scope, 6.10.3.5
macro parameter, 6.10.3
macro preprocessor, 6.10
macro replacement, 6.10.3
magnitude, complex, 7.3.8.1
main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4,
7.19.3
malloc function, 7.20.3, 7.20.3.2, 7.20.3.3,
7.20.3.4
manipulation functions
complex, 7.3.9
real, 7.12.11, F.9.8
matching failure, 7.24.2.6, 7.24.2.8, 7.24.2.10
math.h header, 5.2.4.2.2, 6.5, 7.12, 7.22, F, F.9,
J.5.17
MATH_ERREXCEPT macro, 7.12, F.9
math_errhandling macro, 7.1.3, 7.12, F.9
MATH_ERRNO macro, 7.12
maximum functions, 7.12.12, F.9.9
MB_CUR_MAX macro, 7.1.1, 7.20, 7.20.7.2,
7.20.7.3, 7.24.6.3.3
MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.20
mblen function, 7.20.7.1, 7.24.6.3
mbrlen function, 7.24.6.3.1
mbrtowc function, 7.19.3, 7.19.6.1, 7.19.6.2,
7.24.2.1, 7.24.2.2, 7.24.6.3.1, 7.24.6.3.2,
7.24.6.4.1

532

WG14/N1256

n-char sequence, 7.20.1.3
n-wchar sequence, 7.24.4.1.1
nameexternal, 5.2.4.1, 6.4.2.1, 6.11.3
file, 7.19.3
internal, 5.2.4.1, 6.4.2.1

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

octal-character escape sequence (\octal digits),
6.4.4.4
offsetof macro, 7.17
on-off switch, 6.10.6
ones’ complement, 6.2.6.2
operand, 6.4.6, 6.5
operating system, 5.1.2.1, 7.20.4.6
operations on files, 7.19.4
operator, 6.4.6
operators, 6.5
assignment, 6.5.16
associativity, 6.5
equality, 6.5.9
multiplicative, 6.5.5, G.5.1
postfix, 6.5.2
precedence, 6.5
preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
relational, 6.5.8
shift, 6.5.7
unary, 6.5.3
unary arithmetic, 6.5.3.3
or macro, 7.9
OR operators
bitwise exclusive (^), 6.5.11
bitwise exclusive assignment (^=), 6.5.16.2
bitwise inclusive (|), 6.5.12
bitwise inclusive assignment (|=), 6.5.16.2
logical (||), 6.5.14
or_eq macro, 7.9
order of allocated storage, 7.20.3
order of evaluation, 6.5
ordinary identifier name space, 6.2.3
orientation of stream, 7.19.2, 7.24.3.5
outer scope, 6.2.1

label, 6.2.3
structure/union member, 6.2.3
name spaces, 6.2.3
named label, 6.8.1
NaN, 5.2.4.2.2
nan functions, 7.12.11.2, F.2.1, F.9.8.2
NAN macro, 7.12, F.2.1
NDEBUG macro, 7.2
nearbyint functions, 7.12.9.3, 7.12.9.4, F.3,
F.9.6.3
nearbyint type-generic macro, 7.22
nearest integer functions, 7.12.9, F.9.6
negation operator (!), 6.5.3.3
negative zero, 6.2.6.2, 7.12.11.1
new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4
new-line escape sequence (\n), 5.2.2, 6.4.4.4,
7.4.1.10
nextafter functions, 7.12.11.3, 7.12.11.4, F.3,
F.9.8.3
nextafter type-generic macro, 7.22
nexttoward functions, 7.12.11.4, F.3, F.9.8.4
nexttoward type-generic macro, 7.22
no linkage, 6.2.2
non-stop floating-point control mode, 7.6.4.2
nongraphic characters, 5.2.2, 6.4.4.4
nonlocal jumps header, 7.13
norm, complex, 7.3.8.1
not macro, 7.9
not-equal-to operator, see inequality operator
not_eq macro, 7.9
null character (\0), 5.2.1, 6.4.4.4, 6.4.5
padding of binary stream, 7.19.2
NULL macro, 7.11, 7.17, 7.19.1, 7.20, 7.21.1,
7.23.1, 7.24.1
null pointer, 6.3.2.3
null pointer constant, 6.3.2.3
null preprocessing directive, 6.10.7
null statement, 6.8.3
null wide character, 7.1.1
number classification macros, 7.12, 7.12.3.1
numeric conversion functions, 7.8.2.3, 7.20.1
wide string, 7.8.2.4, 7.24.4.1
numerical limits, 5.2.4.2

paddingbinary stream, 7.19.2
bits, 6.2.6.2, 7.18.1.1
structure/union, 6.2.6.1, 6.7.2.1
parameter, 3.15
array, 6.9.1
ellipsis, 6.7.5.3, 6.10.3
function, 6.5.2.2, 6.7, 6.9.1
macro, 6.10.3
main function, 5.1.2.2.1
program, 5.1.2.2.1
parameter type list, 6.7.5.3
parentheses punctuator (( )), 6.7.5.3, 6.8.4, 6.8.5
parenthesized expression, 6.5.1
parse state, 7.19.2
permitted form of initializer, 6.6

object, 3.14
object representation, 6.2.6.1
object type, 6.2.5
object-like macro, 6.10.3
obsolescence, 6.11, 7.26
octal constant, 6.4.4.1
octal digit, 6.4.4.1, 6.4.4.4

Index

533

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

PRIcPTR macros, 7.8.1
primary expression, 6.5.1
printf function, 7.19.1, 7.19.6.3, 7.19.6.10
printing character, 5.2.2, 7.4, 7.4.1.8
printing wide character, 7.25.2
program diagnostics, 7.2.1
program execution, 5.1.2.2.2, 5.1.2.3
program file, 5.1.1.1
program image, 5.1.1.2
program name (argv[0]), 5.1.2.2.1
program parameters, 5.1.2.2.1
program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1
program structure, 5.1.1.1
program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3,
5.1.2.3
program, conforming, 4program, strictly conforming, 4promotions
default argument, 6.5.2.2
integer, 5.1.2.3, 6.3.1.1
prototype, see function prototype
pseudo-random sequence functions, 7.20.2
PTRDIFF_MAX macro, 7.18.3
PTRDIFF_MIN macro, 7.18.3
ptrdiff_t type, 7.17, 7.18.3, 7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2
punctuators, 6.4.6
putc function, 7.19.1, 7.19.7.8, 7.19.7.9
putchar function, 7.19.1, 7.19.7.9
puts function, 7.19.1, 7.19.7.10
putwc function, 7.19.1, 7.24.3.8, 7.24.3.9
putwchar function, 7.19.1, 7.24.3.9

perror function, 7.19.10.4
phase angle, complex, 7.3.9.1
physical source lines, 5.1.1.2
placemarker, 6.10.3.3
plus operator, unary, 6.5.3.3
pointer arithmetic, 6.5.6
pointer comparison, 6.5.8
pointer declarator, 6.7.5.1
pointer operator (−>), 6.5.2.3
pointer to function, 6.5.2.2
pointer type, 6.2.5
pointer type conversion, 6.3.2.1, 6.3.2.3
pointer, null, 6.3.2.3
portability, 4, J
position indicator, file, see file position indicator
positive difference, 7.12.12.1
positive difference functions, 7.12.12, F.9.9
postfix decrement operator (−−), 6.3.2.1, 6.5.2.4
postfix expressions, 6.5.2
postfix increment operator (++), 6.3.2.1, 6.5.2.4
pow functions, 7.12.7.4, F.9.4.4
pow type-generic macro, 7.22
power functions
complex, 7.3.8, G.6.4
real, 7.12.7, F.9.4
pp-number, 6.4.8
pragma operator, 6.10.9
pragma preprocessing directive, 6.10.6, 6.11.8
precedence of operators, 6.5
precedence of syntax rules, 5.1.1.2
precision, 6.2.6.2, 6.3.1.1, 7.19.6.1, 7.24.2.1
excess, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, 6.8.6.4
predefined macro names, 6.10.8, 6.11.9
prefix decrement operator (−−), 6.3.2.1, 6.5.3.1
prefix increment operator (++), 6.3.2.1, 6.5.3.1
preprocessing concatenation, 6.10.3.3
preprocessing directives, 5.1.1.2, 6.10
preprocessing file, 5.1.1.1, 6.10
preprocessing numbers, 6.4, 6.4.8
preprocessing operators#, 6.10.3.2##, 6.10.3.3_Pragma, 5.1.1.2, 6.10.9
defined, 6.10.1
preprocessing tokens, 5.1.1.2, 6.4, 6.10
preprocessing translation unit, 5.1.1.1
preprocessor, 6.10
PRIcFASTN macros, 7.8.1
PRIcLEASTN macros, 7.8.1
PRIcMAX macros, 7.8.1
PRIcN macros, 7.8.1

534

WG14/N1256

qsort function, 7.20.5, 7.20.5.2
qualified types, 6.2.5
qualified version of type, 6.2.5
question-mark escape sequence (\?), 6.4.4.4
quiet NaN, 5.2.4.2.2
raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.20.4.1
rand function, 7.20, 7.20.2.1, 7.20.2.2
RAND_MAX macro, 7.20, 7.20.2.1
range
excess, 5.2.4.2.2, 6.3.1.5, 6.3.1.8, 6.8.6.4
range error, 7.12.1, 7.12.5.3, 7.12.5.4, 7.12.5.5,
7.12.6.1, 7.12.6.2, 7.12.6.3, 7.12.6.5,
7.12.6.6, 7.12.6.7, 7.12.6.8, 7.12.6.9,
7.12.6.10, 7.12.6.11, 7.12.6.13, 7.12.7.3,
7.12.7.4, 7.12.8.2, 7.12.8.3, 7.12.8.4,
7.12.9.5, 7.12.9.7, 7.12.11.3, 7.12.12.1,
7.12.13.1

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

rank, see integer conversion rank
real floating type conversion, 6.3.1.4, 6.3.1.5,
6.3.1.7, F.3, F.4
real floating types, 6.2.5
real type domain, 6.2.5
real types, 6.2.5
real-floating, 7.12.3
realloc function, 7.20.3, 7.20.3.2, 7.20.3.4
recommended practice, 3.16
recursion, 6.5.2.2
recursive function call, 6.5.2.2
redefinition of macro, 6.10.3
reentrancy, 5.1.2.3, 5.2.3
library functions, 7.1.4
referenced type, 6.2.5
register storage-class specifier, 6.7.1, 6.9
relational expressions, 6.5.8
reliability of data, interrupted, 5.1.2.3
remainder assignment operator (%=), 6.5.16.2
remainder functions, 7.12.10, F.9.7
remainder functions, 7.12.10.2, 7.12.10.3, F.3,
F.9.7.2
remainder operator (%), 6.5.5
remainder type-generic macro, 7.22
remove function, 7.19.4.1, 7.19.4.4
remquo functions, 7.12.10.3, F.3, F.9.7.3
remquo type-generic macro, 7.22
rename function, 7.19.4.2
representations of types, 6.2.6
pointer, 6.2.5
rescanning and replacement, 6.10.3.4
reserved identifiers, 6.4.1, 7.1.3
restartable multibyte/wide character conversion
functions, 7.24.6.3
restartable multibyte/wide string conversion
functions, 7.24.6.4
restore calling environment function, 7.13.2
restrict type qualifier, 6.7.3, 6.7.3.1
restrict-qualified type, 6.2.5, 6.7.3
return statement, 6.8.6.4
rewind function, 7.19.5.3, 7.19.7.11, 7.19.9.5,
7.24.3.10
right-shift assignment operator (>>=), 6.5.16.2
right-shift operator (>>), 6.5.7
rint functions, 7.12.9.4, F.3, F.9.6.4
rint type-generic macro, 7.22
round functions, 7.12.9.6, F.9.6.6
round type-generic macro, 7.22
rounding mode, floating point, 5.2.4.2.2
rvalue, 6.3.2.1

ISO/IEC 9899:TC3

same scope, 6.2.1
save calling environment function, 7.13.1
scalar types, 6.2.5
scalbln function, 7.12.6.13, F.3, F.9.3.13
scalbln type-generic macro, 7.22
scalbn function, 7.12.6.13, F.3, F.9.3.13
scalbn type-generic macro, 7.22
scanf function, 7.19.1, 7.19.6.4, 7.19.6.11
scanlist, 7.19.6.2, 7.24.2.2
scanset, 7.19.6.2, 7.24.2.2
SCHAR_MAX macro, 5.2.4.2.1
SCHAR_MIN macro, 5.2.4.2.1
SCNcFASTN macros, 7.8.1
SCNcLEASTN macros, 7.8.1
SCNcMAX macros, 7.8.1
SCNcN macros, 7.8.1
SCNcPTR macros, 7.8.1
scope of identifier, 6.2.1, 6.9.2
search functions
string, 7.21.5
utility, 7.20.5
wide string, 7.24.4.5
SEEK_CUR macro, 7.19.1, 7.19.9.2
SEEK_END macro, 7.19.1, 7.19.9.2
SEEK_SET macro, 7.19.1, 7.19.9.2
selection statements, 6.8.4
self-referential structure, 6.7.2.3
semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3,
6.8.5, 6.8.6
separate compilation, 5.1.1.1
separate translation, 5.1.1.1
sequence points, 5.1.2.3, 6.5, 6.8, 7.1.4, 7.19.6,
7.20.5, 7.24.2, C
sequencing of statements, 6.8
setbuf function, 7.19.3, 7.19.5.1, 7.19.5.5
setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1
setjmp.h header, 7.13
setlocale function, 7.11.1.1, 7.11.2.1
setvbuf function, 7.19.1, 7.19.3, 7.19.5.1,
7.19.5.5, 7.19.5.6
shall, 4
shift expressions, 6.5.7
shift sequence, 7.1.1
shift states, 5.2.1.2
short identifier, character, 5.2.4.1, 6.4.3
short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2
short int type conversion, 6.3.1.1, 6.3.1.3,
6.3.1.4, 6.3.1.8
SHRT_MAX macro, 5.2.4.2.1
SHRT_MIN macro, 5.2.4.2.1

Index

535

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

source lines, 5.1.1.2
source text, 5.1.1.2
space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,
7.4.1.10, 7.25.2.1.3
sprintf function, 7.19.6.6, 7.19.6.13
sqrt functions, 7.12.7.5, F.3, F.9.4.5
sqrt type-generic macro, 7.22
srand function, 7.20.2.2
sscanf function, 7.19.6.7, 7.19.6.14
standard error stream, 7.19.1, 7.19.3, 7.19.10.4
standard headers, 4, 7.1.2<assert.h>, 7.2, B.1<complex.h>, 5.2.4.2.2, 7.3, 7.22, 7.26.1,
G.6, J.5.17<ctype.h>, 7.4, 7.26.2<errno.h>, 7.5, 7.26.3<fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H
<float.h>, 4, 5.2.4.2.2, 7.7, 7.20.1.3,
7.24.4.1.1<inttypes.h>, 7.8, 7.26.4<iso646.h>, 4, 7.9<limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10
<locale.h>, 7.11, 7.26.5<math.h>, 5.2.4.2.2, 6.5, 7.12, 7.22, F, F.9,
J.5.17<setjmp.h>, 7.13
<signal.h>, 7.14, 7.26.6<stdarg.h>, 4, 6.7.5.3, 7.15
<stdbool.h>, 4, 7.16, 7.26.7, H<stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
6.4.5, 6.5.3.4, 6.5.6, 7.17
<stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.18,
7.26.8<stdio.h>, 5.2.4.2.2, 7.19, 7.26.9, F<stdlib.h>, 5.2.4.2.2, 7.20, 7.26.10, F<string.h>, 7.21, 7.26.11<tgmath.h>, 7.22, G.7<time.h>, 7.23
<wchar.h>, 5.2.4.2.2, 7.19.1, 7.24, 7.26.12,
F<wctype.h>, 7.25, 7.26.13
standard input stream, 7.19.1, 7.19.3
standard integer types, 6.2.5
standard output stream, 7.19.1, 7.19.3
standard signed integer types, 6.2.5
state-dependent encoding, 5.2.1.2, 7.20.7
statements, 6.8
break, 6.8.6.3
compound, 6.8.2
continue, 6.8.6.2
do, 6.8.5.2

side effects, 5.1.2.3, 6.5
SIG_ATOMIC_MAX macro, 7.18.3
SIG_ATOMIC_MIN macro, 7.18.3
sig_atomic_t type, 7.14, 7.14.1.1, 7.18.3
SIG_DFL macro, 7.14, 7.14.1.1
SIG_ERR macro, 7.14, 7.14.1.1
SIG_IGN macro, 7.14, 7.14.1.1
SIGABRT macro, 7.14, 7.20.4.1
SIGFPE macro, 7.14, 7.14.1.1, J.5.17
SIGILL macro, 7.14, 7.14.1.1
SIGINT macro, 7.14
sign and magnitude, 6.2.6.2
sign bit, 6.2.6.2
signal function, 7.14.1.1, 7.20.4.4
signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1
signal handling functions, 7.14.1
signal.h header, 7.14, 7.26.6
signaling NaN, 5.2.4.2.2, F.2.1
signals, 5.1.2.3, 5.2.3, 7.14.1
signbit macro, 7.12.3.6, F.3
signed char type, 6.2.5, 7.19.6.1, 7.19.6.2,
7.24.2.1, 7.24.2.2
signed character, 6.3.1.1
signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1
signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
6.3.1.8
signed types, 6.2.5, 6.7.2
significand part, 6.4.4.2
SIGSEGV macro, 7.14, 7.14.1.1
SIGTERM macro, 7.14
simple assignment operator (=), 6.5.16.1
sin functions, 7.12.4.6, F.9.1.6
sin type-generic macro, 7.22, G.7
single-byte character, 3.7.1, 5.2.1.2
single-byte/wide character conversion functions,7.24.6.1
single-precision arithmetic, 5.1.2.3
single-quote escape sequence (\'), 6.4.4.4, 6.4.5
sinh functions, 7.12.5.5, F.9.2.5
sinh type-generic macro, 7.22, G.7
SIZE_MAX macro, 7.18.3
size_t type, 6.5.3.4, 7.17, 7.18.3, 7.19.1,
7.19.6.1, 7.19.6.2, 7.20, 7.21.1, 7.23.1,
7.24.1, 7.24.2.1, 7.24.2.2
sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4
snprintf function, 7.19.6.5, 7.19.6.12
sorting utility functions, 7.20.5
source character set, 5.1.1.2, 5.2.1
source file, 5.1.1.1
name, 6.10.4, 6.10.8
source file inclusion, 6.10.2

536

WG14/N1256

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

strictly conforming program, 4string, 7.1.1
comparison functions, 7.21.4
concatenation functions, 7.21.3
conversion functions, 7.11.1.1
copying functions, 7.21.2
library function conventions, 7.21.1
literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.8
miscellaneous functions, 7.21.6
numeric conversion functions, 7.8.2.3, 7.20.1
search functions, 7.21.5
string handling header, 7.21
string.h header, 7.21, 7.26.11
stringizing, 6.10.3.2, 6.10.9
strlen function, 7.21.6.3
strncat function, 7.21.3.2
strncmp function, 7.21.4, 7.21.4.4
strncpy function, 7.21.2.4
strpbrk function, 7.21.5.4
strrchr function, 7.21.5.5
strspn function, 7.21.5.6
strstr function, 7.21.5.7
strtod function, 7.12.11.2, 7.19.6.2, 7.20.1.3,
7.24.2.2, F.3
strtof function, 7.12.11.2, 7.20.1.3, F.3
strtoimax function, 7.8.2.3
strtok function, 7.21.5.8
strtol function, 7.8.2.3, 7.19.6.2, 7.20.1.2,
7.20.1.4, 7.24.2.2
strtold function, 7.12.11.2, 7.20.1.3, F.3
strtoll function, 7.8.2.3, 7.20.1.2, 7.20.1.4
strtoul function, 7.8.2.3, 7.19.6.2, 7.20.1.2,
7.20.1.4, 7.24.2.2
strtoull function, 7.8.2.3, 7.20.1.2, 7.20.1.4
strtoumax function, 7.8.2.3
struct hack, see flexible array member
structurearrow operator (−>), 6.5.2.3
content, 6.7.2.3
dot operator (.), 6.5.2.3
initialization, 6.7.8
member alignment, 6.7.2.1
member name space, 6.2.3
member operator (.), 6.3.2.1, 6.5.2.3
pointer operator (−>), 6.5.2.3
specifier, 6.7.2.1
tag, 6.2.3, 6.7.2.3
type, 6.2.5, 6.7.2.1
strxfrm function, 7.11.1.1, 7.21.4.5
subscripting, 6.5.2.1
subtraction assignment operator (−=), 6.5.16.2

else, 6.8.4.1
expression, 6.8.3
for, 6.8.5.3
goto, 6.8.6.1
if, 6.8.4.1
iteration, 6.8.5
jump, 6.8.6
labeled, 6.8.1
null, 6.8.3
return, 6.8.6.4
selection, 6.8.4
sequencing, 6.8
switch, 6.8.4.2
while, 6.8.5.1
static storage duration, 6.2.4
static storage-class specifier, 6.2.2, 6.2.4, 6.7.1
static, in array declarators, 6.7.5.2, 6.7.5.3
stdarg.h header, 4, 6.7.5.3, 7.15
stdbool.h header, 4, 7.16, 7.26.7, H
STDC, 6.10.6, 6.11.8
stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
6.4.5, 6.5.3.4, 6.5.6, 7.17
stderr macro, 7.19.1, 7.19.2, 7.19.3
stdin macro, 7.19.1, 7.19.2, 7.19.3, 7.19.6.4,
7.19.7.6, 7.19.7.7, 7.24.2.12, 7.24.3.7
stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.18,
7.26.8
stdio.h header, 5.2.4.2.2, 7.19, 7.26.9, F
stdlib.h header, 5.2.4.2.2, 7.20, 7.26.10, F
stdout macro, 7.19.1, 7.19.2, 7.19.3, 7.19.6.3,
7.19.7.9, 7.19.7.10, 7.24.2.11, 7.24.3.9
storage duration, 6.2.4
storage order of array, 6.5.2.1
storage-class specifiers, 6.7.1, 6.11.5
strcat function, 7.21.3.1
strchr function, 7.21.5.2
strcmp function, 7.21.4, 7.21.4.2
strcoll function, 7.11.1.1, 7.21.4.3, 7.21.4.5
strcpy function, 7.21.2.3
strcspn function, 7.21.5.3
streams, 7.19.2, 7.20.4.3
fully buffered, 7.19.3
line buffered, 7.19.3
orientation, 7.19.2
standard error, 7.19.1, 7.19.3
standard input, 7.19.1, 7.19.3
standard output, 7.19.1, 7.19.3
unbuffered, 7.19.3
strerror function, 7.19.10.4, 7.21.6.2
strftime function, 7.11.1.1, 7.23.3, 7.23.3.5,
7.24.5.1

Index

537

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

tolower function, 7.4.2.1
toupper function, 7.4.2.2
towctrans function, 7.25.3.2.1, 7.25.3.2.2
towlower function, 7.25.3.1.1, 7.25.3.2.1
towupper function, 7.25.3.1.2, 7.25.3.2.1
translation environment, 5, 5.1.1
translation limits, 5.2.4.1
translation phases, 5.1.1.2
translation unit, 5.1.1.1, 6.9
trap representation, 6.2.6.1, 6.2.6.2, 6.3.2.3,
6.5.2.3
trigonometric functions
complex, 7.3.5, G.6.1
real, 7.12.4, F.9.1
trigraph sequences, 5.1.1.2, 5.2.1.1
true macro, 7.16
trunc functions, 7.12.9.8, F.9.6.8
trunc type-generic macro, 7.22
truncation, 6.3.1.4, 7.12.9.8, 7.19.3, 7.19.5.3
truncation toward zero, 6.5.5
two’s complement, 6.2.6.2, 7.18.1.1
type category, 6.2.5
type conversion, 6.3
type definitions, 6.7.7
type domain, 6.2.5, G.2
type names, 6.7.6
type punning, 6.5.2.3
type qualifiers, 6.7.3
type specifiers, 6.7.2
type-generic macro, 7.22, G.7
typedef declaration, 6.7.7
typedef storage-class specifier, 6.7.1, 6.7.7
types, 6.2.5
character, 6.7.8
compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.5
complex, 6.2.5, G
composite, 6.2.7
const qualified, 6.7.3
conversions, 6.3
imaginary, G
restrict qualified, 6.7.3
volatile qualified, 6.7.3

subtraction operator (−), 6.5.6, F.3, G.5.2
suffixfloating constant, 6.4.4.2
integer constant, 6.4.4.1
switch body, 6.8.4.2
switch case label, 6.8.1, 6.8.4.2
switch default label, 6.8.1, 6.8.4.2
switch statement, 6.8.1, 6.8.4.2
swprintf function, 7.24.2.3, 7.24.2.7
swscanf function, 7.24.2.4, 7.24.2.8
symbols, 3
syntactic categories, 6.1
syntax notation, 6.1
syntax rule precedence, 5.1.1.2
syntax summary, language, A
system function, 7.20.4.6
tab characters, 5.2.1, 6.4
tag compatibility, 6.2.7
tag name space, 6.2.3
tags, 6.7.2.3
tan functions, 7.12.4.7, F.9.1.7
tan type-generic macro, 7.22, G.7
tanh functions, 7.12.5.6, F.9.2.6
tanh type-generic macro, 7.22, G.7
tentative definition, 6.9.2
terms, 3
text streams, 7.19.2, 7.19.7.11, 7.19.9.2, 7.19.9.4
tgamma functions, 7.12.8.4, F.9.5.4
tgamma type-generic macro, 7.22
tgmath.h header, 7.22, G.7
timebroken down, 7.23.1, 7.23.2.3, 7.23.3, 7.23.3.1,
7.23.3.3, 7.23.3.4, 7.23.3.5
calendar, 7.23.1, 7.23.2.2, 7.23.2.3, 7.23.2.4,
7.23.3.2, 7.23.3.3, 7.23.3.4
components, 7.23.1
conversion functions, 7.23.3
wide character, 7.24.5
local, 7.23.1
manipulation functions, 7.23.2
time function, 7.23.2.4
time.h header, 7.23
time_t type, 7.23.1
tm structure type, 7.23.1, 7.24.1
TMP_MAX macro, 7.19.1, 7.19.4.3, 7.19.4.4
tmpfile function, 7.19.4.3, 7.20.4.3
tmpnam function, 7.19.1, 7.19.4.3, 7.19.4.4
token, 5.1.1.2, 6.4, see also preprocessing tokens
token concatenation, 6.10.3.3
token pasting, 6.10.3.3

538

WG14/N1256

UCHAR_MAX macro, 5.2.4.2.1
UINT_FASTN_MAX macros, 7.18.2.3
uint_fastN_t types, 7.18.1.3
UINT_LEASTN_MAX macros, 7.18.2.2
uint_leastN_t types, 7.18.1.2
UINT_MAX macro, 5.2.4.2.1
UINTMAX_C macro, 7.18.4.2
UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.18.2.5

Index

WG14/N1256

Committee Draft — Septermber 7, 2007

ISO/IEC 9899:TC3

USHRT_MAX macro, 5.2.4.2.1
usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6,
6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15
utilities, general, 7.20
wide string, 7.24.4

uintmax_t type, 7.18.1.5, 7.19.6.1, 7.19.6.2,
7.24.2.1, 7.24.2.2
UINTN_C macros, 7.18.4.1
UINTN_MAX macros, 7.18.2.1
uintN_t types, 7.18.1.1
UINTPTR_MAX macro, 7.18.2.4
uintptr_t type, 7.18.1.4
ULLONG_MAX macro, 5.2.4.2.1, 7.20.1.4,
7.24.4.1.2
ULONG_MAX macro, 5.2.4.2.1, 7.20.1.4,
7.24.4.1.2
unary arithmetic operators, 6.5.3.3
unary expression, 6.5.3
unary minus operator (−), 6.5.3.3, F.3
unary operators, 6.5.3
unary plus operator (+), 6.5.3.3
unbuffered stream, 7.19.3
undef preprocessing directive, 6.10.3.5, 7.1.3,
7.1.4
undefined behavior, 3.4.3, 4, J.2
underscore character, 6.4.2.1
underscore, leading, in identifier, 7.1.3
ungetc function, 7.19.1, 7.19.7.11, 7.19.9.2,
7.19.9.3
ungetwc function, 7.19.1, 7.24.3.10
Unicode required set, 6.10.8
unionarrow operator (−>), 6.5.2.3
content, 6.7.2.3
dot operator (.), 6.5.2.3
initialization, 6.7.8
member alignment, 6.7.2.1
member name space, 6.2.3
member operator (.), 6.3.2.1, 6.5.2.3
pointer operator (−>), 6.5.2.3
specifier, 6.7.2.1
tag, 6.2.3, 6.7.2.3
type, 6.2.5, 6.7.2.1
universal character name, 6.4.3
unqualified type, 6.2.5
unqualified version of type, 6.2.5
unsigned integer suffix, u or U, 6.4.4.1
unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1
unsigned type conversion, 6.3.1.1, 6.3.1.3,
6.3.1.4, 6.3.1.8
unsigned types, 6.2.5, 6.7.2, 7.19.6.1, 7.19.6.2,
7.24.2.1, 7.24.2.2
unspecified behavior, 3.4.4, 4, J.1
unspecified value, 3.17.3
uppercase letter, 5.2.1
use of library functions, 7.1.4

va_arg macro, 7.15, 7.15.1, 7.15.1.1, 7.15.1.2,
7.15.1.4, 7.19.6.8, 7.19.6.9, 7.19.6.10,
7.19.6.11, 7.19.6.12, 7.19.6.13, 7.19.6.14,
7.24.2.5, 7.24.2.6, 7.24.2.7, 7.24.2.8,
7.24.2.9, 7.24.2.10
va_copy macro, 7.15, 7.15.1, 7.15.1.1, 7.15.1.2,
7.15.1.3
va_end macro, 7.1.3, 7.15, 7.15.1, 7.15.1.3,
7.15.1.4, 7.19.6.8, 7.19.6.9, 7.19.6.10,
7.19.6.11, 7.19.6.12, 7.19.6.13, 7.19.6.14,
7.24.2.5, 7.24.2.6, 7.24.2.7, 7.24.2.8,
7.24.2.9, 7.24.2.10
va_list type, 7.15, 7.15.1.3
va_start macro, 7.15, 7.15.1, 7.15.1.1,
7.15.1.2, 7.15.1.3, 7.15.1.4, 7.19.6.8,
7.19.6.9, 7.19.6.10, 7.19.6.11, 7.19.6.12,
7.19.6.13, 7.19.6.14, 7.24.2.5, 7.24.2.6,
7.24.2.7, 7.24.2.8, 7.24.2.9, 7.24.2.10
value, 3.17
value bits, 6.2.6.2
variable arguments, 6.10.3, 7.15
variable arguments header, 7.15
variable length array, 6.7.5, 6.7.5.2
variably modified type, 6.7.5, 6.7.5.2
vertical-tab character, 5.2.1, 6.4vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4,
7.4.1.10
vfprintf function, 7.19.1, 7.19.6.8
vfscanf function, 7.19.1, 7.19.6.8, 7.19.6.9
vfwprintf function, 7.19.1, 7.24.2.5
vfwscanf function, 7.19.1, 7.24.2.6, 7.24.3.10
visibility of identifier, 6.2.1
VLA, see variable length arrayvoid expression, 6.3.2.2
void function parameter, 6.7.5.3
void type, 6.2.5, 6.3.2.2, 6.7.2
void type conversion, 6.3.2.2
volatile storage, 5.1.2.3
volatile type qualifier, 6.7.3
volatile-qualified type, 6.2.5, 6.7.3
vprintf function, 7.19.1, 7.19.6.8, 7.19.6.10
vscanf function, 7.19.1, 7.19.6.8, 7.19.6.11
vsnprintf function, 7.19.6.8, 7.19.6.12
vsprintf function, 7.19.6.8, 7.19.6.13
vsscanf function, 7.19.6.8, 7.19.6.14

Index

539

ISO/IEC 9899:TC3

Committee Draft — Septermber 7, 2007

wctype.h header, 7.25, 7.26.13
wctype_t type, 7.25.1, 7.25.2.2.2
WEOF macro, 7.24.1, 7.24.3.1, 7.24.3.3, 7.24.3.6,
7.24.3.7, 7.24.3.8, 7.24.3.9, 7.24.3.10,
7.24.6.1.1, 7.25.1
while statement, 6.8.5.1
white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10,
7.25.2.1.10
white-space characters, 6.4
wide character, 3.7.3
case mapping functions, 7.25.3.1
extensible, 7.25.3.2
classification functions, 7.25.2.1
extensible, 7.25.2.2
constant, 6.4.4.4
formatted input/output functions, 7.24.2
input functions, 7.19.1
input/output functions, 7.19.1, 7.24.3
output functions, 7.19.1
single-byte conversion functions, 7.24.6.1
wide string, 7.1.1
wide string comparison functions, 7.24.4.4
wide string concatenation functions, 7.24.4.3
wide string copying functions, 7.24.4.2
wide string literal, see string literalwide string miscellaneous functions, 7.24.4.6
wide string numeric conversion functions, 7.8.2.4,
7.24.4.1
wide string search functions, 7.24.4.5
wide-oriented stream, 7.19.2
width, 6.2.6.2
WINT_MAX macro, 7.18.3
WINT_MIN macro, 7.18.3
wint_t type, 7.18.3, 7.19.6.1, 7.24.1, 7.24.2.1,
7.25.1
wmemchr function, 7.24.4.5.8
wmemcmp function, 7.24.4.4.5
wmemcpy function, 7.24.4.2.3
wmemmove function, 7.24.4.2.4
wmemset function, 7.24.4.6.2
wprintf function, 7.19.1, 7.24.2.9, 7.24.2.11
wscanf function, 7.19.1, 7.24.2.10, 7.24.2.12,
7.24.3.10

vswprintf function, 7.24.2.7
vswscanf function, 7.24.2.8
vwprintf function, 7.19.1, 7.24.2.9
vwscanf function, 7.19.1, 7.24.2.10, 7.24.3.10
warnings, I
wchar.h header, 5.2.4.2.2, 7.19.1, 7.24, 7.26.12,
F
WCHAR_MAX macro, 7.18.3, 7.24.1
WCHAR_MIN macro, 7.18.3, 7.24.1
wchar_t type, 3.7.3, 6.4.4.4, 6.4.5, 6.7.8,
6.10.8, 7.17, 7.18.3, 7.19.6.1, 7.19.6.2, 7.20,
7.24.1, 7.24.2.1, 7.24.2.2
wcrtomb function, 7.19.3, 7.19.6.2, 7.24.2.2,
7.24.6.3.3, 7.24.6.4.2
wcscat function, 7.24.4.3.1
wcschr function, 7.24.4.5.1
wcscmp function, 7.24.4.4.1, 7.24.4.4.4
wcscoll function, 7.24.4.4.2, 7.24.4.4.4
wcscpy function, 7.24.4.2.1
wcscspn function, 7.24.4.5.2
wcsftime function, 7.11.1.1, 7.24.5.1
wcslen function, 7.24.4.6.1
wcsncat function, 7.24.4.3.2
wcsncmp function, 7.24.4.4.3
wcsncpy function, 7.24.4.2.2
wcspbrk function, 7.24.4.5.3
wcsrchr function, 7.24.4.5.4
wcsrtombs function, 7.24.6.4.2
wcsspn function, 7.24.4.5.5
wcsstr function, 7.24.4.5.6
wcstod function, 7.19.6.2, 7.24.2.2
wcstod function, 7.24.4.1.1
wcstof function, 7.24.4.1.1
wcstoimax function, 7.8.2.4
wcstok function, 7.24.4.5.7
wcstol function, 7.8.2.4, 7.19.6.2, 7.24.2.2,
7.24.4.1.2
wcstold function, 7.24.4.1.1
wcstoll function, 7.8.2.4, 7.24.4.1.2
wcstombs function, 7.20.8.2, 7.24.6.4
wcstoul function, 7.8.2.4, 7.19.6.2, 7.24.2.2,
7.24.4.1.2
wcstoull function, 7.8.2.4, 7.24.4.1.2
wcstoumax function, 7.8.2.4
wcsxfrm function, 7.24.4.4.4
wctob function, 7.24.6.1.2, 7.25.2.1
wctomb function, 7.20.7.3, 7.20.8.2, 7.24.6.3
wctrans function, 7.25.3.2.1, 7.25.3.2.2
wctrans_t type, 7.25.1, 7.25.3.2.2
wctype function, 7.25.2.2.1, 7.25.2.2.2

540

WG14/N1256

xor macro, 7.9
xor_eq macro, 7.9

Index