# fprintf

## 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



           dprintf, fprintf, printf, snprintf, sprintf — print formatted
           output
    


## SYNOPSIS



           #include <stdio.h>
    
           int dprintf(int _fildes_ , const char *restrict _format_ , ...);
           int fprintf(FILE *restrict _stream_ , const char *restrict _format_ , ...);
           int printf(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_ , ...);
    


## DESCRIPTION



           Excluding _dprintf_(): 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 _fprintf_() function shall place output on the named output
           _stream_.  The _printf_() function shall place output on the standard
           output stream _stdout_.  The _sprintf_() function shall place output
           followed by the null byte, **'\0'** , in consecutive bytes starting at
           *_s_ ; it is the user's responsibility to ensure that enough space is
           available.
    
           The _dprintf_() function shall be equivalent to the _fprintf_()
           function, except that _dprintf_() shall write output to the file
           associated with the file descriptor specified by the _fildes_
           argument rather than place output on a stream.
    
           The _snprintf_() function shall be equivalent to _sprintf_(), with the
           addition of the _n_ argument which states the size of the buffer
           referred to by _s_.  If _n_ is zero, nothing shall be written and _s_
           may be a null pointer. Otherwise, output bytes beyond the _n_ ‐1st
           shall be discarded instead of being written to the array, and a
           null byte is written at the end of the bytes actually written into
           the array.
    
           If copying takes place between objects that overlap as a result of
           a call to _sprintf_() or _snprintf_(), the results are undefined.
    
           Each of these functions converts, formats, and prints its
           arguments under control of the _format_.  The _format_ is a character
           string, beginning and ending in its initial shift state, if any.
           The _format_ is composed of zero or more directives: _ordinary_
           _characters_ , which are simply copied to the output stream, and
           _conversion specifications_ , each of which shall result in the
           fetching of zero or more arguments.  The results are undefined if
           there are insufficient arguments for the _format_.  If the _format_ is
           exhausted while arguments remain, the excess arguments shall be
           evaluated but are 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}], giving the position of the argument in
           the argument list. This feature provides for the definition of
           format strings that select arguments in an order appropriate to
           specific languages (see the EXAMPLES section).
    
           The _format_ can contain either numbered argument conversion
           specifications (that is, "%_n_ $" and "*_m_ $"), or unnumbered argument
           conversion specifications (that is, **%** and *****), but not both. The
           only exception to this is that **%%** can be mixed with the "%_n_ $"
           form. The results of mixing numbered and unnumbered argument
           specifications in a _format_ string are undefined. 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 specified in the format string.
    
           In format strings containing the "%_n_ $" form of conversion
           specification, numbered arguments in the argument list can be
           referenced from the format string as many times as required.
    
           In format strings containing the **%** form of conversion
           specification, each conversion specification uses the first unused
           argument in the argument list.
    
           All forms of the _fprintf_() functions allow for the insertion of a
           language-dependent radix character in the output 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>
           (**'.'**).
    
           Each conversion specification is introduced by the **'%'** character
           or by the character sequence "%_n_ $", after which the following
           appear in sequence:
    
            *  Zero or more _flags_ (in any order), which modify the meaning of
               the conversion specification.
    
            *  An optional minimum _field width_.  If the converted value has
               fewer bytes than the field width, it shall be padded with
               <space> characters by default on the left; it shall be padded
               on the right if the left-adjustment flag (**'-'**), described
               below, is given to the field width. The field width takes the
               form of an <asterisk> (**'*'**), described below, or a decimal
               integer.
    
            *  An optional _precision_ that gives the minimum number of digits
               to appear for the **d** , **i** , **o** , **u** , **x** , and **X** conversion specifiers;
               the number of digits to appear after the radix character for
               the **a** , **A** , **e** , **E** , **f** , and **F** conversion specifiers; the maximum
               number of significant digits for the **g** and **G** conversion
               specifiers; or the maximum number of bytes to be printed from
               a string in the **s** and **S** conversion specifiers. The precision
               takes the form of a <period> (**'.'**)  followed either by an
               <asterisk> (**'*'**), described below, or an optional decimal
               digit string, where a null digit string is treated as zero. If
               a precision appears with any other conversion specifier, the
               behavior is undefined.
    
            *  An optional length modifier that specifies the size of the
               argument.
    
            *  A _conversion specifier_ character that indicates the type of
               conversion to be applied.
    
           A field width, or precision, or both, may be indicated by an
           <asterisk> (**'*'**).  In this case an argument of type **int** supplies
           the field width or precision. Applications shall ensure that
           arguments specifying field width, or precision, or both appear in
           that order before the argument, if any, to be converted. A
           negative field width is taken as a **'-'** flag followed by a positive
           field width. A negative precision is taken as if the precision
           were omitted.  In _format_ strings containing the "%_n_ $" form of a
           conversion specification, a field width or precision may be
           indicated by the sequence "*_m_ $", where _m_ is a decimal integer in
           the range [1,{NL_ARGMAX}] giving the position in the argument list
           (after the _format_ argument) of an integer argument containing the
           field width or precision, for example:
    
               printf("%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);
    
           The flag characters and their meanings are:
    
           '       (The <apostrophe>.)  The integer portion of the result of
                   a decimal conversion (**%i** , **%d** , **%u** , **%f** , **%F** , **%g** , or **%G**) shall
                   be formatted with thousands' grouping characters. For
                   other conversions the behavior is undefined. The non-
                   monetary grouping character is used.
    
           -       The result of the conversion shall be left-justified
                   within the field.  The conversion is right-justified if
                   this flag is not specified.
    
           +       The result of a signed conversion shall always begin with
                   a sign (**'+'** or **'-'**).  The conversion shall begin with a
                   sign only when a negative value is converted if this flag
                   is not specified.
    
           <space> If the first character of a signed conversion is not a
                   sign or if a signed conversion results in no characters, a
                   <space> shall be prefixed to the result. This means that
                   if the <space> and **'+'** flags both appear, the <space> flag
                   shall be ignored.
    
           #       Specifies that the value is to be converted to an
                   alternative form. For **o** conversion, it shall increase the
                   precision, if and only if necessary, to force the first
                   digit of the result to be a zero (if the value and
                   precision are both 0, a single 0 is printed). For **x** or **X**
                   conversion specifiers, a non-zero result shall have 0x (or
                   0X) prefixed to it. For **a** , **A** , **e** , **E** , **f** , **F** , **g** , and **G**
                   conversion specifiers, the result shall always contain a
                   radix character, even if no digits follow the radix
                   character. Without this flag, a radix character appears in
                   the result of these conversions only if a digit follows
                   it. For **g** and **G** conversion specifiers, trailing zeros
                   shall _not_ be removed from the result as they normally are.
                   For other conversion specifiers, the behavior is
                   undefined.
    
           0       For **d** , **i** , **o** , **u** , **x** , **X** , **a** , **A** , **e** , **E** , **f** , **F** , **g** , and **G**
                   conversion specifiers, 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** conversion specifiers, if a precision is specified,
                   the **'0'** flag shall be ignored.  If the **'0'** and
                   <apostrophe> flags both appear, the grouping characters
                   are inserted before zero padding. For other conversions,
                   the behavior is undefined.
    
           The length modifiers and their meanings are:
    
           hh      Specifies that a following **d** , **i** , **o** , **u** , **x** , or **X** conversion
                   specifier applies to a **signed char** or **unsigned char**
                   argument (the argument will have been promoted according
                   to the integer promotions, but its value shall be
                   converted to **signed char** or **unsigned char** before
                   printing); or that a following **n** conversion specifier
                   applies to a pointer to a **signed char** argument.
    
           h       Specifies that a following **d** , **i** , **o** , **u** , **x** , or **X** conversion
                   specifier applies to a **short** or **unsigned short** argument
                   (the argument will have been promoted according to the
                   integer promotions, but its value shall be converted to
                   **short** or **unsigned short** before printing); or that a
                   following **n** conversion specifier applies to a pointer to a
                   **short** argument.
    
           l (ell) Specifies that a following **d** , **i** , **o** , **u** , **x** , or **X** conversion
                   specifier applies to a **long** or **unsigned long** argument;
                   that a following **n** conversion specifier applies to a
                   pointer to a **long** argument; that a following **c** conversion
                   specifier applies to a **wint_t** argument; that a following **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 a **long long** or **unsigned long long**
                   argument; or that a following **n** conversion specifier
                   applies to a pointer to a **long long** argument.
    
           j       Specifies that a following **d** , **i** , **o** , **u** , **x** , or **X** conversion
                   specifier applies to an **intmax_t** or **uintmax_t** argument; or
                   that a following **n** conversion specifier applies to a
                   pointer to an **intmax_t** argument.
    
           z       Specifies that a following **d** , **i** , **o** , **u** , **x** , or **X** conversion
                   specifier applies to a **size_t** or the corresponding signed
                   integer type argument; or that a following **n** conversion
                   specifier applies to a pointer to a signed integer type
                   corresponding to a **size_t** argument.
    
           t       Specifies that a following **d** , **i** , **o** , **u** , **x** , or **X** conversion
                   specifier applies to a **ptrdiff_t** or the corresponding
                   **unsigned** type argument; or that a following **n** conversion
                   specifier applies to a pointer to a **ptrdiff_t** argument.
    
           L       Specifies 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.
    
           The conversion specifiers and their meanings are:
    
           d, i    The **int** argument shall be converted to a 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 shall be expanded
                   with leading zeros. The default precision is 1. The result
                   of converting zero with an explicit precision of zero
                   shall be no characters.
    
           o       The **unsigned** argument shall be converted to unsigned octal
                   format 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 shall be
                   expanded with leading zeros. The default precision is 1.
                   The result of converting zero with an explicit precision
                   of zero shall be no characters.
    
           u       The **unsigned** argument shall be converted to unsigned
                   decimal format 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 shall be expanded with leading zeros. The default
                   precision is 1. The result of converting zero with an
                   explicit precision of zero shall be no characters.
    
           x       The **unsigned** argument shall be converted to unsigned
                   hexadecimal format in the style "_dddd_ "; the letters
                   **"abcdef"** are used. The precision specifies the minimum
                   number of digits to appear; if the value being converted
                   can be represented in fewer digits, it shall be expanded
                   with leading zeros. The default precision is 1. The result
                   of converting zero with an explicit precision of zero
                   shall be no characters.
    
           X       Equivalent to the **x** conversion specifier, except that
                   letters **"ABCDEF"** are used instead of **"abcdef"**.
    
           f, F    The **double** argument shall be converted to decimal notation
                   in the style "[-]_ddd_._ddd_ ", where the number of digits
                   after the radix character is equal to the precision
                   specification. If the precision is missing, it shall be
                   taken as 6; if the precision is explicitly zero and no **'#'**
                   flag is present, no radix character shall appear. If a
                   radix character appears, at least one digit appears before
                   it. The low-order digit shall be rounded in an
                   implementation-defined manner.
    
                   A **double** argument representing an infinity shall be
                   converted in one of the styles **"[-]inf"** or **"[-]infinity"** ;
                   which style is implementation-defined. A **double** argument
                   representing a NaN shall be converted in one of the styles
                   "[-]nan(_n-char-sequence_)" or **"[-]nan"** ; 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.
    
           e, E    The **double** argument shall be converted in the style
                   "[-]_d_._ddd_ e± _dd_ ", where there is one digit before the radix
                   character (which is non-zero if the argument is non-zero)
                   and the number of digits after it is equal to the
                   precision; if the precision is missing, it shall be taken
                   as 6; if the precision is zero and no **'#'** flag is present,
                   no radix character shall appear. The low-order digit shall
                   be rounded in an implementation-defined manner. The **E**
                   conversion specifier shall produce a number with **'E'**
                   instead of **'e'** introducing the exponent. The exponent
                   shall always contain at least two digits. If the value is
                   zero, the exponent shall be zero.
    
                   A **double** argument representing an infinity or NaN shall be
                   converted in the style of an **f** or **F** conversion specifier.
    
           g, G    The **double** argument representing a floating-point number
                   shall be converted in the style **f** or **e**(or in the 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 non-zero, 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 shall be with style **f**(or **F**)
                       and precision **P** -(_X_ +1).
    
                   --  Otherwise, the conversion shall be with style **e**(or **E**)
                       and precision **P** -1.
    
                   Finally, unless the **'#'** flag is used, any trailing zeros
                   shall be removed from the fractional portion of the result
                   and the decimal-point character shall be removed if there
                   is no fractional portion remaining.
    
                   A **double** argument representing an infinity or NaN shall be
                   converted in the style of an **f** or **F** conversion specifier.
    
           a, A    A **double** argument representing a floating-point number
                   shall be converted in the style "[-]0x _h_._hhhh_ p± _d_ ", where
                   there is one hexadecimal digit (which shall be non-zero if
                   the argument is a normalized floating-point number and is
                   otherwise unspecified) before the decimal-point character
                   and the number 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 shall be sufficient
                   for an exact representation of the value; if the precision
                   is missing and FLT_RADIX is not a power of 2, then the
                   precision shall be sufficient to distinguish values of
                   type **double** , except that trailing zeros may be omitted; if
                   the precision is zero and the **'#'** flag is not specified,
                   no decimal-point character shall appear. The letters
                   **"abcdef"** shall be 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 shall always contain at least one digit, and
                   only as many more digits as necessary to represent the
                   decimal exponent of 2. If the value is zero, the exponent
                   shall be zero.
    
                   A **double** argument representing an infinity or NaN shall be
                   converted in the style of an **f** or **F** conversion specifier.
    
           c       The **int** argument shall be converted to an **unsigned char** ,
                   and the resulting byte shall be written.
    
                   If an **l**(ell) qualifier is present, the **wint_t** argument
                   shall be converted as if by an **ls** conversion specification
                   with no precision and an argument that points to a two-
                   element array of type **wchar_t** , the first element of which
                   contains the **wint_t** argument to the **ls** conversion
                   specification and the second element contains a null wide
                   character.
    
           s       The argument shall be a pointer to an array of **char**.
                   Bytes from the array shall be written up to (but not
                   including) any terminating null byte. If the precision is
                   specified, no more than that many bytes shall be written.
                   If the precision is not specified or is greater than the
                   size of the array, the application shall ensure that the
                   array contains a null byte.
    
                   If an **l**(ell) qualifier is present, the argument shall be
                   a pointer to an array of type **wchar_t**.  Wide characters
                   from the array shall be converted to 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 and including a terminating null wide
                   character. The resulting characters shall be written up to
                   (but not including) the terminating null character (byte).
                   If no precision is specified, the application shall ensure
                   that the array contains a null wide character.  If a
                   precision is specified, no more than that many characters
                   (bytes) shall be written (including shift sequences, if
                   any), and the array shall contain a null wide character
                   if, to equal the character sequence length given by the
                   precision, the function would need to access a wide
                   character one past the end of the array. In no case shall
                   a partial character be written.
    
           p       The argument shall be a pointer to **void**.  The value of the
                   pointer is converted to a sequence of printable
                   characters, in an implementation-defined manner.
    
           n       The argument shall be a pointer to an integer into which
                   is written the number of bytes written to the output so
                   far by this call to one of the _fprintf_() functions. No
                   argument is converted.
    
           C       Equivalent to **lc**.
    
           S       Equivalent to **ls**.
    
           %       Print a **'%'** character; no argument is converted. The
                   complete conversion specification shall be **%%**.
    
           If a conversion specification does not match one of the above
           forms, the behavior is undefined. If any argument is not the
           correct type for the corresponding conversion specification, the
           behavior is undefined.
    
           In no case shall a nonexistent or small field width cause
           truncation of a field; if the result of a conversion is wider than
           the field width, the field shall be expanded to contain the
           conversion result.  Characters generated by _fprintf_() and _printf_()
           are printed as if _fputc_() had been called.
    
           For the **a** and **A** conversion specifiers, if FLT_RADIX is a power of
           2, the value shall be correctly rounded to a hexadecimal floating
           number with the given precision.
    
           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 the error should have a correct sign for the
           current rounding direction.
    
           For the **e** , **E** , **f** , **F** , **g** , and **G** conversion specifiers, if the number
           of significant decimal digits is at most DECIMAL_DIG, then the
           result should be correctly rounded. If the number of significant
           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 value of the
           resultant decimal string _D_ should satisfy _L_ <= _D_ <= _U_ , with the
           extra stipulation that the error should have a correct sign for
           the current rounding direction.
    
           The last data modification and last file status change timestamps
           of the file shall be marked for update:
    
            1. Between the call to a successful execution of _fprintf_() or
               _printf_() and the next successful completion of a call to
               _fflush_() or _fclose_() on the same stream or a call to _exit_() or
               _abort_()
    
            2. Upon successful completion of a call to _dprintf_()
    


## RETURN VALUE



           Upon successful completion, the _dprintf_(), _fprintf_(), and _printf_()
           functions shall return the number of bytes transmitted.
    
           Upon successful completion, the _sprintf_() function shall return
           the number of bytes written to _s_ , excluding the terminating null
           byte.
    
           Upon successful completion, the _snprintf_() function shall return
           the number of bytes that would be written to _s_ had _n_ been
           sufficiently large excluding the terminating null byte.
    
           If an output error was encountered, these functions shall return a
           negative value and set _errno_ to indicate the error.
    
           If the value of _n_ is zero on a call to _snprintf_(), nothing shall
           be written, the number of bytes that would have been written had _n_
           been sufficiently large excluding the terminating null shall be
           returned, and _s_ may be a null pointer.
    


## ERRORS



           For the conditions under which _dprintf_(), _fprintf_(), and _printf_()
           fail and may fail, refer to fputc(3p) or fputwc(3p).
    
           In addition, all forms of _fprintf_() shall fail if:
    
           **EILSEQ** A wide-character code that does not correspond to a valid
                  character has been detected.
    
           **EOVERFLOW**
                  The value to be returned is greater than {INT_MAX}.
    
           The _dprintf_() function may fail if:
    
           **EBADF** The _fildes_ argument is not a valid file descriptor.
    
           The _dprintf_(), _fprintf_(), and _printf_() functions may fail if:
    
           **ENOMEM** Insufficient storage space is available.
    
           The _snprintf_() function shall fail if:
    
           **EOVERFLOW**
                  The value of _n_ is greater than {INT_MAX}.
    
           _The following sections are informative._
    


## EXAMPLES



       **Printing Language-Independent Date and Time**
           The following statement can be used to print date and time using a
           language-independent format:
    
               printf(format, weekday, month, day, hour, min);
    
           For American usage, _format_ could be a pointer to the following
           string:
    
               "%s, %s %d, %d:%.2d\n"
    
           This example would produce the following message:
    
               Sunday, July 3, 10:02
    
           For German usage, _format_ could be a pointer to the following
           string:
    
               "%1$s, %3$d. %2$s, %4$d:%5$.2d\n"
    
           This definition of _format_ would produce the following message:
    
               Sonntag, 3. Juli, 10:02
    
       **Printing File Information**
           The following example prints information about the type,
           permissions, and number of links of a specific file in a
           directory.
    
           The first two calls to _printf_() use data decoded from a previous
           _stat_() call. The user-defined _strperm_() function shall return a
           string similar to the one at the beginning of the output for the
           following command:
    
               ls -l
    
           The next call to _printf_() outputs the owner's name if it is found
           using _getpwuid_(); the _getpwuid_() function shall return a **passwd**
           structure from which the name of the user is extracted. If the
           user name is not found, the program instead prints out the numeric
           value of the user ID.
    
           The next call prints out the group name if it is found using
           _getgrgid_(); _getgrgid_() is very similar to _getpwuid_() except that
           it shall return group information based on the group number.  Once
           again, if the group is not found, the program prints the numeric
           value of the group for the entry.
    
           The final call to _printf_() prints the size of the file.
    
               #include <stdio.h>
               #include <sys/types.h>
               #include <pwd.h>
               #include <grp.h>
    
               char *strperm (mode_t);
               ...
               struct stat statbuf;
               struct passwd *pwd;
               struct group *grp;
               ...
               printf("%10.10s", strperm (statbuf.st_mode));
               printf("%4d", statbuf.st_nlink);
    
               if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
                   printf(" %-8.8s", pwd->pw_name);
               else
                   printf(" %-8ld", (long) statbuf.st_uid);
    
               if ((grp = getgrgid(statbuf.st_gid)) != NULL)
                   printf(" %-8.8s", grp->gr_name);
               else
                   printf(" %-8ld", (long) statbuf.st_gid);
    
               printf("%9jd", (intmax_t) statbuf.st_size);
               ...
    
       **Printing a Localized Date String**
           The following example gets a localized date string. The
           _nl_langinfo_() function shall return the localized date string,
           which specifies the order and layout of the date. The _strftime_()
           function takes this information and, using the **tm** structure for
           values, places the date and time information into _datestring_.  The
           _printf_() function then outputs _datestring_ and the name of the
           entry.
    
               #include <stdio.h>
               #include <time.h>
               #include <langinfo.h>
               ...
               struct dirent *dp;
               struct tm *tm;
               char datestring[256];
               ...
               strftime(datestring, sizeof(datestring), nl_langinfo (D_T_FMT), tm);
    
               printf(" %s %s\n", datestring, dp->d_name);
               ...
    
       **Printing Error Information**
           The following example uses _fprintf_() to write error information to
           standard error.
    
           In the first group of calls, the program tries to open the
           password lock file named **LOCKFILE**.  If the file already exists,
           this is an error, as indicated by the O_EXCL flag on the _open_()
           function. If the call fails, the program assumes that someone else
           is updating the password file, and the program exits.
    
           The next group of calls saves a new password file as the current
           password file by creating a link between **LOCKFILE** and the new
           password file **PASSWDFILE**.
    
               #include <sys/types.h>
               #include <sys/stat.h>
               #include <fcntl.h>
               #include <stdio.h>
               #include <stdlib.h>
               #include <unistd.h>
               #include <string.h>
               #include <errno.h>
    
               #define LOCKFILE "/etc/ptmp"
               #define PASSWDFILE "/etc/passwd"
               ...
               int pfd;
               ...
               if ((pfd = open(LOCKFILE, O_WRONLY | O_CREAT | O_EXCL,
                   S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) == -1)
               {
                   fprintf(stderr, "Cannot open /etc/ptmp. Try again later.\n");
                   exit(1);
               }
               ...
               if (link(LOCKFILE,PASSWDFILE) == -1) {
                   fprintf(stderr, "Link error: %s\n", strerror(errno));
                   exit(1);
               }
               ...
    
       **Printing Usage Information**
           The following example checks to make sure the program has the
           necessary arguments, and uses _fprintf_() to print usage information
           if the expected number of arguments is not present.
    
               #include <stdio.h>
               #include <stdlib.h>
               ...
               char *Options = "hdbtl";
               ...
               if (argc < 2) {
                   fprintf(stderr, "Usage: %s -%s <file\n", argv[0], Options); exit(1);
               }
               ...
    
       **Formatting a Decimal String**
           The following example prints a key and data pair on _stdout_.  Note
           use of the <asterisk> (**'*'**) in the format string; this ensures the
           correct number of decimal places for the element based on the
           number of elements requested.
    
               #include <stdio.h>
               ...
               long i;
               char *keystr;
               int elementlen, len;
               ...
               while (len < elementlen) {
               ...
                   printf("%s Element%0*ld\n", keystr, elementlen, i);
               ...
               }
    
       **Creating a Pathname**
           The following example creates a pathname using information from a
           previous _getpwnam_() function that returned the password database
           entry of the user.
    
               #include <stdint.h>
               #include <stdio.h>
               #include <stdlib.h>
               #include <string.h>
               #include <sys/types.h>
               #include <unistd.h>
               ...
               char *pathname;
               struct passwd *pw;
               size_t len;
               ...
               // digits required for pid_t is number of bits times
               // log2(10) = approx 10/33
               len = strlen(pw->pw_dir) + 1 + 1+(sizeof(pid_t)*80+32)/33 +
                   sizeof ".out";
               pathname = malloc(len);
               if (pathname != NULL)
               {
                   snprintf(pathname, len, "%s/%jd.out", pw->pw_dir,
                       (intmax_t)getpid());
                   ...
               }
    
       **Reporting an Event**
           The following example loops until an event has timed out. The
           _pause_() function waits forever unless it receives a signal. The
           _fprintf_() statement should never occur due to the possible return
           values of _pause_().
    
               #include <stdio.h>
               #include <unistd.h>
               #include <string.h>
               #include <errno.h>
               ...
               while (!event_complete) {
               ...
                   if (pause() != -1 || errno != EINTR)
                       fprintf(stderr, "pause: unknown error: %s\n", strerror(errno));
               }
               ...
    
       **Printing Monetary Information**
           The following example uses _strfmon_() to convert a number and store
           it as a formatted monetary string named _convbuf_.  If the first
           number is printed, the program prints the format and the
           description; otherwise, it just prints the number.
    
               #include <monetary.h>
               #include <stdio.h>
               ...
               struct tblfmt {
                   char *format;
                   char *description;
               };
    
               struct tblfmt table[] = {
                   { "%n", "default formatting" },
                   { "%11n", "right align within an 11 character field" },
                   { "%#5n", "aligned columns for values up to 99999" },
                   { "%=*#5n", "specify a fill character" },
                   { "%=0#5n", "fill characters do not use grouping" },
                   { "%^#5n", "disable the grouping separator" },
                   { "%^#5.0n", "round off to whole units" },
                   { "%^#5.4n", "increase the precision" },
                   { "%(#5n", "use an alternative pos/neg style" },
                   { "%!(#5n", "disable the currency symbol" },
               };
               ...
               float input[3];
               int i, j;
               char convbuf[100];
               ...
               strfmon(convbuf, sizeof(convbuf), table[i].format, input[j]);
    
               if (j == 0) {
                   printf("%s%s%s\n", table[i].format,
                       convbuf, table[i].description);
               }
               else {
                   printf("%s\n", convbuf);
               }
               ...
    
       **Printing Wide Characters**
           The following example prints a series of wide characters. Suppose
           that **"L`@`"** expands to three bytes:
    
               wchar_t wz [3] = L"@@";       // Zero-terminated
               wchar_t wn [3] = L"@@@";      // Unterminated
    
               fprintf (stdout,"%ls", wz);   // Outputs 6 bytes
               fprintf (stdout,"%ls", wn);   // Undefined because wn has no terminator
               fprintf (stdout,"%4ls", wz);  // Outputs 3 bytes
               fprintf (stdout,"%4ls", wn);  // Outputs 3 bytes; no terminator needed
               fprintf (stdout,"%9ls", wz);  // Outputs 6 bytes
               fprintf (stdout,"%9ls", wn);  // Outputs 9 bytes; no terminator needed
               fprintf (stdout,"%10ls", wz); // Outputs 6 bytes
               fprintf (stdout,"%10ls", wn); // Undefined because wn has no terminator
    
           In the last line of the example, after processing three
           characters, nine bytes have been output. The fourth character must
           then be examined to determine whether it converts to one byte or
           more. If it converts to more than one byte, the output is only
           nine bytes. Since there is no fourth character in the array, the
           behavior is undefined.
    


## APPLICATION USAGE



           If the application calling _fprintf_() has any objects of type
           **wint_t** or **wchar_t** , it must also include the _< wchar.h>_ header to
           have these objects defined.
    


## RATIONALE



           If an implementation detects that there are insufficient arguments
           for the format, it is recommended that the function should fail
           and report an **[EINVAL]** error.
    


## FUTURE DIRECTIONS



           None.
    


* * *