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FPRINTF(3P)               POSIX Programmer's Manual              FPRINTF(3P)

PROLOG         top

       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         top

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

SYNOPSIS         top

       #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         top

       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.1‐2008 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 nth 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 Nth 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 increases the precision (if
               necessary) to force the first digit of the result to be zero.
               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.ddddd", 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 "[−]0xh.hhhhd", 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         top

       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         top

       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}.

       In addition, all forms of fprintf() may fail if:

       EINVAL There are insufficient arguments.

       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         top

   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         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.5, Standard I/O Streams, fputc(3p), fscanf(3p),
       setlocale(3p), strfmon(3p), wcrtomb(3p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale,
       stdio.h(0p), wchar.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                         FPRINTF(3P)