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

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 require‐
       ments described here and the ISO C standard is unintentional. This vol‐
       ume 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, begin‐
       ning and ending in its initial shift state, if any. The format is  com‐
       posed 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  for‐
       mat.   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 specifica‐
       tions (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  specifica‐
       tion,  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  lan‐
       guage-dependent radix character in the output string. The radix charac‐
       ter 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> charac‐
	   ters 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 num‐
	   ber of digits to appear after the radix character for the a, A,  e,
	   E,  f,  and F conversion specifiers; the maximum number of signifi‐
	   cant 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 conver‐
	   sion 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 speci‐
	   fier, the behavior is undefined.

	*  An optional length modifier that specifies the size	of  the	 argu‐
	   ment.

	*  A conversion specifier character that indicates the type of conver‐
	   sion 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 con‐
	       versions 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 speci‐
	       fied.

       <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	neces‐
	       sary)  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  conver‐
	       sions only if a digit follows it. For g and G conversion speci‐
	       fiers, trailing zeros shall not be removed from the  result  as
	       they  normally are. For other conversion specifiers, the behav‐
	       ior 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 behav‐
	       ior is undefined.

       The length modifiers and their meanings are:

       hh      Specifies that a following d, i, o, u, x, or X conversion spec‐
	       ifier applies to a signed char or unsigned char	argument  (the
	       argument	 will have been promoted according to the integer pro‐
	       motions, but its value shall be converted  to  signed  char  or
	       unsigned	 char  before printing); or that a following n conver‐
	       sion specifier applies to a pointer to a signed char argument.

       h       Specifies that a following d, i, o, u, x, or X conversion spec‐
	       ifier  applies to a short or unsigned short argument (the argu‐
	       ment will have been promoted according to  the  integer	promo‐
	       tions,  but  its	 value shall be converted to short or unsigned
	       short before printing); or that a following n conversion speci‐
	       fier applies to a pointer to a short argument.

       l (ell) Specifies that a following d, i, o, u, x, or X conversion spec‐
	       ifier applies to a long or unsigned long argument; that a  fol‐
	       lowing  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 spec‐
	       ifier 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 spec‐
	       ifier  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 spec‐
	       ifier 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 spec‐
	       ifier 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	repre‐
	       sented  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 for‐
	       mat 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 hexadeci‐
	       mal 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  dig‐
	       its,  it shall be expanded with leading zeros. The default pre‐
	       cision 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 charac‐
	       ter  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.ddde±dd", where there is one digit before the radix char‐
	       acter (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  implementa‐
	       tion-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 con‐
	       verted 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 con‐
	       verted 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 frac‐
	       tional portion remaining.

	       A double argument representing an infinity or NaN shall be con‐
	       verted 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.hhhhp±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 hexadeci‐
	       mal 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	 deci‐
	       mal-point character shall appear. The letters "abcdef" shall be
	       used for a conversion and the letters "ABCDEF"  for  A  conver‐
	       sion. 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 con‐
	       verted 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 ele‐
	       ment 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	appli‐
	       cation 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.   Charac‐
       ters  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  dig‐
       its  is	more  than  DECIMAL_DIG but the source value is exactly repre‐
       sentable 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 neg‐
       ative 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() or fputwc().

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

       EILSEQ A	 wide-character code that does not correspond to a valid char‐
	      acter 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
   Printing Language-Independent Date and Time
       The following statement can be used to print date and time using a lan‐
       guage-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 get‐
       grgid(); 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 infor‐
       mation and, using the tm structure for values, places the date and time
       information  into  datestring.  The printf() function then outputs dat‐
       estring 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 pass‐
       word file, and the program exits.

       The  next group of calls saves a new password file as the current pass‐
       word 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 ele‐
       ments 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  pre‐
       vious  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
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section	2.5,  Standard	I/O  Streams,  fputc(), fscanf(), setlocale(),
       strfmon(), wcrtomb()

       The  Base  Definitions  volume  of  POSIX.1‐2008,  Chapter  7,  Locale,
       <stdio.h>, <wchar.h>

COPYRIGHT
       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 Electri‐
       cal  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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			   FPRINTF(3P)
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