# fscanf

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           fscanf, scanf, sscanf — convert formatted input
    


## SYNOPSIS



           #include <stdio.h>
    
           int fscanf(FILE *restrict _stream_ , const char *restrict _format_ , ...);
           int scanf(const char *restrict _format_ , ...);
           int sscanf(const char *restrict _s_ , const char *restrict _format_ , ...);
    


## DESCRIPTION



           The functionality described on this reference page is aligned with
           the ISO C standard. Any conflict between the requirements
           described here and the ISO C standard is unintentional. This
           volume of POSIX.1‐2017 defers to the ISO C standard.
    
           The _fscanf_() function shall read from the named input _stream_.  The
           _scanf_() function shall read from the standard input stream _stdin_.
           The _sscanf_() function shall read from the string _s_.  Each function
           reads bytes, interprets them according to a format, and stores the
           results in its arguments. Each expects, as arguments, a control
           string _format_ described below, and a set of _pointer_ arguments
           indicating where the converted input should be stored. The result
           is undefined if there are insufficient arguments for the format.
           If the format is exhausted while arguments remain, the excess
           arguments shall be evaluated but otherwise ignored.
    
           Conversions can be applied to the _n_ th argument after the _format_ in
           the argument list, rather than to the next unused argument. In
           this case, the conversion specifier character **%**(see below) is
           replaced by the sequence "%_n_ $", where _n_ is a decimal integer in
           the range [1,{NL_ARGMAX}].  This feature provides for the
           definition of format strings that select arguments in an order
           appropriate to specific languages. In format strings containing
           the "%_n_ $" form of conversion specifications, it is unspecified
           whether numbered arguments in the argument list can be referenced
           from the format string more than once.
    
           The _format_ can contain either form of a conversion specification—
           that is, **%** or "%_n_ $"—but the two forms cannot be mixed within a
           single _format_ string. The only exception to this is that **%%** or **%***
           can be mixed with the "%_n_ $" form. When numbered argument
           specifications are used, specifying the _N_ th argument requires that
           all the leading arguments, from the first to the (_N_ -1)th, are
           pointers.
    
           The _fscanf_() function in all its forms shall allow detection of a
           language-dependent radix character in the input string. The radix
           character is defined in the current locale (category _LC_NUMERIC_).
           In the POSIX locale, or in a locale where the radix character is
           not defined, the radix character shall default to a <period>
           (**'.'**).
    
           The format is a character string, beginning and ending in its
           initial shift state, if any, composed of zero or more directives.
           Each directive is composed of one of the following: one or more
           white-space characters (<space>, <tab>, <newline>, <vertical-tab>,
           or <form-feed>); an ordinary character (neither **'%'** nor a white-
           space character); or a conversion specification. Each conversion
           specification is introduced by the character **'%'** or the character
           sequence "%_n_ $", after which the following appear in sequence:
    
            *  An optional assignment-suppressing character **'*'**.
    
            *  An optional non-zero decimal integer that specifies the
               maximum field width.
    
            *  An optional assignment-allocation character **'m'**.
    
            *  An option length modifier that specifies the size of the
               receiving object.
    
            *  A _conversion specifier_ character that specifies the type of
               conversion to be applied. The valid conversion specifiers are
               described below.
    
           The _fscanf_() functions shall execute each directive of the format
           in turn. If a directive fails, as detailed below, the function
           shall return. Failures are described as input failures (due to the
           unavailability of input bytes) or matching failures (due to
           inappropriate input).
    
           A directive composed of one or more white-space characters shall
           be executed by reading input until no more valid input can be
           read, or up to the first byte which is not a white-space
           character, which remains unread.
    
           A directive that is an ordinary character shall be executed as
           follows: the next byte shall be read from the input and compared
           with the byte that comprises the directive; if the comparison
           shows that they are not equivalent, the directive shall fail, and
           the differing and subsequent bytes shall remain unread. Similarly,
           if end-of-file, an encoding error, or a read error prevents a
           character from being read, the directive shall fail.
    
           A directive that is a conversion specification defines a set of
           matching input sequences, as described below for each conversion
           character. A conversion specification shall be executed in the
           following steps.
    
           Input white-space characters (as specified by isspace(3p)) shall
           be skipped, unless the conversion specification includes a **[** , **c** ,
           **C** , or **n** conversion specifier.
    
           An item shall be read from the input, unless the conversion
           specification includes an **n** conversion specifier. An input item
           shall be defined as the longest sequence of input bytes (up to any
           specified maximum field width, which may be measured in characters
           or bytes dependent on the conversion specifier) which is an
           initial subsequence of a matching sequence. The first byte, if
           any, after the input item shall remain unread. If the length of
           the input item is 0, the execution of the conversion specification
           shall fail; this condition is a matching 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.
    
           Except in the case of a **%** conversion specifier, the input item
           (or, in the case of a **%n** conversion specification, the count of
           input bytes) shall be converted to a type appropriate to the
           conversion character. If the input item is not a matching
           sequence, the execution of the conversion specification fails;
           this condition is a matching failure. Unless assignment
           suppression was indicated by a **'*'** , the result of the conversion
           shall be placed in the object pointed to by the first argument
           following the _format_ argument that has not already received a
           conversion result if the conversion specification is introduced by
           **%** , or in the _n_ th argument if introduced by the character sequence
           "%_n_ $".  If this object does not have an appropriate type, or if
           the result of the conversion cannot be represented in the space
           provided, the behavior is undefined.
    
           The **%c** , **%s** , and **%[** conversion specifiers shall accept an optional
           assignment-allocation character **'m'** , which shall cause a memory
           buffer to be allocated to hold the string converted including a
           terminating null character. In such a case, the argument
           corresponding to the conversion specifier should be a reference to
           a pointer variable that will receive a pointer to the allocated
           buffer. The system shall allocate a buffer as if _malloc_() had been
           called. The application shall be responsible for freeing the
           memory after usage. If there is insufficient memory to allocate a
           buffer, the function shall set _errno_ to **[ENOMEM]** and a conversion
           error shall result. If the function returns EOF, any memory
           successfully allocated for parameters using assignment-allocation
           character **'m'** by this call shall be freed before the function
           returns.
    
           The length modifiers and their meanings are:
    
           hh      Specifies 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**.
    
           h       Specifies that a following **d** , **i** , **o** , **u** , **x** , **X** , or **n**
                   conversion specifier applies to an argument with type
                   pointer to **short** or **unsigned short**.
    
           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** or **unsigned long** ; that a following **a** , **A** ,
                   **e** , **E** , **f** , **F** , **g** , or **G** conversion specifier applies to an
                   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**.  If the **'m'** assignment-
                   allocation character is specified, the conversion applies
                   to an argument with the type pointer to a 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** or **unsigned long long**.
    
           j       Specifies 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**.
    
           z       Specifies 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** 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.
    
           The following conversion specifiers are valid:
    
           d       Matches an optionally signed decimal integer, whose format
                   is the same as expected for the subject sequence of
                   _strtol_() with the value 10 for the _base_ argument. In the
                   absence of a size modifier, the application shall ensure
                   that the corresponding argument is a pointer to **int**.
    
           i       Matches an optionally signed integer, whose format is the
                   same as expected for the subject sequence of _strtol_() with
                   0 for the _base_ argument. In the absence of a size
                   modifier, the application shall ensure that the
                   corresponding argument is a pointer to **int**.
    
           o       Matches an optionally signed octal integer, whose format
                   is the same as expected for the subject sequence of
                   _strtoul_() with the value 8 for the _base_ argument. In the
                   absence of a size modifier, the application shall ensure
                   that the corresponding argument is a pointer to **unsigned**.
    
           u       Matches an optionally signed decimal integer, whose format
                   is the same as expected for the subject sequence of
                   _strtoul_() with the value 10 for the _base_ argument. In the
                   absence of a size modifier, the application shall ensure
                   that the corresponding argument is a pointer to **unsigned**.
    
           x       Matches an optionally signed hexadecimal integer, whose
                   format is the same as expected for the subject sequence of
                   _strtoul_() with the value 16 for the _base_ argument. In the
                   absence of a size modifier, the application shall ensure
                   that the corresponding argument is a pointer to **unsigned**.
    
           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 _strtod_().  In the absence of a
                   size modifier, the application shall ensure that the
                   corresponding argument is a pointer to **float**.
    
                   If the _fprintf_() family of functions generates character
                   string representations for infinity and NaN (a symbolic
                   entity encoded in floating-point format) to support
                   IEEE Std 754‐1985, the _fscanf_() family of functions shall
                   recognize them as input.
    
           s       Matches a sequence of bytes that are not white-space
                   characters. If the **'m'** assignment-allocation character is
                   not specified, the application shall ensure that the
                   corresponding argument is a pointer to the initial byte of
                   an array of **char** , **signed char** , or **unsigned char** large
                   enough to accept the sequence and a terminating null
                   character code, which shall be added automatically.
                   Otherwise, the application shall ensure that the
                   corresponding argument is a pointer to a pointer to a
                   **char**.
    
                   If an **l**(ell) qualifier is present, the input is a
                   sequence of characters that begins in the initial shift
                   state. Each character shall be 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 character is
                   converted.  If the **'m'** assignment-allocation character is
                   not specified, the application shall ensure that the
                   corresponding argument is a pointer to an array of **wchar_t**
                   large enough to accept the sequence and the terminating
                   null wide character, which shall be added automatically.
                   Otherwise, the application shall ensure that the
                   corresponding argument is a pointer to a pointer to a
                   **wchar_t**.
    
           [       Matches a non-empty sequence of bytes from a set of
                   expected bytes (the _scanset_).  The normal skip over white-
                   space characters shall be suppressed in this case. If the
                   **'m'** assignment-allocation character is not specified, the
                   application shall ensure that the corresponding argument
                   is a pointer to the initial byte of an array of **char** ,
                   **signed char** , or **unsigned char** large enough to accept the
                   sequence and a terminating null byte, which shall be added
                   automatically.  Otherwise, the application shall ensure
                   that the corresponding argument is a pointer to a pointer
                   to a **char**.
    
                   If an **l**(ell) qualifier is present, the input is a
                   sequence of characters that begins in the initial shift
                   state. Each character in the sequence shall be 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
                   character is converted.  If the **'m'** assignment-allocation
                   character is not specified, the application shall ensure
                   that the corresponding argument is a pointer to an array
                   of **wchar_t** large enough to accept the sequence and the
                   terminating null wide character, which shall be added
                   automatically.
                   Otherwise, the application shall ensure that the
                   corresponding argument is a pointer to a pointer to a
                   **wchar_t**.
    
                   The conversion specification includes all subsequent bytes
                   in the _format_ string up to and including the matching
                   <right-square-bracket> (**']'**).  The bytes between the
                   square brackets (the _scanlist_) comprise the scanset,
                   unless the byte after the <left-square-bracket> is a
                   <circumflex> (**'^'**), in which case the scanset contains all
                   bytes that do not appear in the scanlist between the
                   <circumflex> and the <right-square-bracket>.  If the
                   conversion specification begins with **"[]"** or **"[^]"** , the
                   <right-square-bracket> is included in the scanlist and the
                   next <right-square-bracket> is the matching <right-square-
                   bracket> that ends the conversion specification;
                   otherwise, the first <right-square-bracket> is the one
                   that ends the conversion specification. If a **'-'** is in the
                   scanlist and is not the first character, nor the second
                   where the first character is a **'^'** , nor the last
                   character, the behavior is implementation-defined.
    
           c       Matches a sequence of bytes of the number specified by the
                   field width (1 if no field width is present in the
                   conversion specification). No null byte is added. The
                   normal skip over white-space characters shall be
                   suppressed in this case. If the **'m'** assignment-allocation
                   character is not specified, the application shall ensure
                   that the corresponding argument is a pointer to the
                   initial byte of an array of **char** , **signed char** , or **unsigned**
                   **char** large enough to accept the sequence.  Otherwise, the
                   application shall ensure that the corresponding argument
                   is a pointer to a pointer to a **char**.
    
                   If an **l**(ell) qualifier is present, the input shall be a
                   sequence of characters that begins in the initial shift
                   state. Each character in the sequence 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 character is
                   converted.  No null wide character is added. If the **'m'**
                   assignment-allocation character is not specified, the
                   application shall ensure that the corresponding argument
                   is a pointer to an array of **wchar_t** large enough to accept
                   the resulting sequence of wide characters.  Otherwise, the
                   application shall ensure that the corresponding argument
                   is a pointer to a pointer to a **wchar_t**.
    
           p       Matches an implementation-defined set of sequences, which
                   shall be the same as the set of sequences that is produced
                   by the **%p** conversion specification of the corresponding
                   _fprintf_() functions. The application shall ensure that the
                   corresponding argument is a pointer to a pointer to **void**.
                   The interpretation of the input item is implementation-
                   defined. 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 specification is undefined.
    
           n       No input is consumed. The application shall ensure that
                   the corresponding argument is a pointer to the integer
                   into which shall be written the number of bytes read from
                   the input so far by this call to the _fscanf_() functions.
                   Execution of a **%n** conversion specification shall not
                   increment the assignment count returned at the completion
                   of execution of the function. No argument shall be
                   converted, but one shall be consumed. If the conversion
                   specification includes an assignment-suppressing character
                   or a field width, the behavior is undefined.
    
           C       Equivalent to **lc**.
    
           S       Equivalent to **ls**.
    
           %       Matches a single **'%'** character; no conversion or
                   assignment occurs. The complete conversion specification
                   shall be **%%**.
    
           If a conversion specification is invalid, the behavior is
           undefined.
    
           The conversion specifiers **A** , **E** , **F** , **G** , and **X** are also valid and
           shall be equivalent to **a** , **e** , **f** , **g** , and **x** , respectively.
    
           If end-of-file is encountered during input, conversion shall be
           terminated. If end-of-file occurs before any bytes matching the
           current conversion specification (except for **%n**) have been read
           (other than leading white-space characters, where permitted),
           execution of the current conversion specification shall terminate
           with an input failure. Otherwise, unless execution of the current
           conversion specification is terminated with a matching failure,
           execution of the following conversion specification (if any) shall
           be terminated with an input failure.
    
           Reaching the end of the string in _sscanf_() shall be equivalent to
           encountering end-of-file for _fscanf_().
    
           If conversion terminates on a conflicting input, the offending
           input is left unread in the input. Any trailing white space
           (including <newline> characters) shall be left unread unless
           matched by a conversion specification. The success of literal
           matches and suppressed assignments is only directly determinable
           via the **%n** conversion specification.
    
           The _fscanf_() and _scanf_() functions may mark the last data access
           timestamp of the file associated with _stream_ for update. The last
           data access timestamp shall be marked for update by the first
           successful execution of _fgetc_(), _fgets_(), _fread_(), _getc_(),
           _getchar_(), _getdelim_(), _getline_(), _gets_(), _fscanf_(), or _scanf_()
           using _stream_ that returns data not supplied by a prior call to
           _ungetc_().
    


## RETURN VALUE



           Upon successful completion, these functions shall return the
           number of successfully matched and assigned input items; this
           number can be zero in the event of an early matching failure. If
           the input ends before the first conversion (if any) has completed,
           and without a matching failure having occurred, EOF shall be
           returned. If an error occurs before the first conversion (if any)
           has completed, and without a matching failure having occurred, EOF
           shall be returned and _errno_ shall be set to indicate the error.
           If a read error occurs, the error indicator for the stream shall
           be set.
    


## ERRORS



           For the conditions under which the _fscanf_() functions fail and may
           fail, refer to fgetc(3p) or fgetwc(3p).
    
           In addition, the _fscanf_() function shall fail if:
    
           **EILSEQ** Input byte sequence does not form a valid character.
    
           **ENOMEM** Insufficient storage space is available.
    
           In addition, the _fscanf_() function may fail if:
    
           **EINVAL** There are insufficient arguments.
    
           _The following sections are informative._
    


## EXAMPLES



           The call:
    
               int i, n; float x; char name[50];
               n = scanf("%d%f%s", &i, &x, name);
    
           with the input line:
    
               25 54.32E-1 Hamster
    
           assigns to _n_ the value 3, to _i_ the value 25, to _x_ the value 5.432,
           and _name_ contains the string **"Hamster"**.
    
           The call:
    
               int i; float x; char name[50];
               (void) scanf("%2d%f%*d %[0123456789]", &i, &x, name);
    
           with input:
    
               56789 0123 56a72
    
           assigns 56 to _i_ , 789.0 to _x_ , skips 0123, and places the string
           **"56\0"** in _name_.  The next call to _getchar_() shall return the
           character **'a'**.
    
       **Reading Data into an Array**
           The following call uses _fscanf_() to read three floating-point
           numbers from standard input into the _input_ array.
    
               float input[3]; fscanf (stdin, "%f %f %f", input, input+1, input+2);
    


## APPLICATION USAGE



           If the application calling _fscanf_() has any objects of type **wint_t**
           or **wchar_t** , it must also include the _< wchar.h>_ header to have
           these objects defined.
    
           For functions that allocate memory as if by _malloc_(), the
           application should release such memory when it is no longer
           required by a call to _free_().  For _fscanf_(), this is memory
           allocated via use of the **'m'** assignment-allocation character.
    


## RATIONALE



           This function is aligned with the ISO/IEC 9899:1999 standard, and
           in doing so a few ``obvious'' things were not included.
           Specifically, the set of characters allowed in a scanset is
           limited to single-byte characters.  In other similar places,
           multi-byte characters have been permitted, but for alignment with
           the ISO/IEC 9899:1999 standard, it has not been done here.
           Applications needing this could use the corresponding wide-
           character functions to achieve the desired results.
    


## FUTURE DIRECTIONS



           None.
    


* * *