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STRFTIME(3) 			    Linux Programmer's Manual			        STRFTIME(3) 

NAME
       strftime - format date and time

SYNOPSIS
       #include <time.h>

       size_t strftime(char *s, size_t max, const char *format,
		       const struct tm *tm);

DESCRIPTION
       The strftime() function formats the broken-down time tm according to the format specifica-
       tion format and places the result in the character array s of size max.

       The format specification is a null-terminated string and  may  contain  special	character
       sequences called conversion specifications, each of which is introduced by a '%' character
       and terminated by some other character known as a  conversion  specifier  character.   All
       other character sequences are ordinary character sequences.

       The characters of ordinary character sequences (including the null byte) are copied verba-
       tim from format to s.  However, the characters of conversion specifications  are  replaced
       as follows:

       %a     The abbreviated weekday name according to the current locale.

       %A     The full weekday name according to the current locale.

       %b     The abbreviated month name according to the current locale.

       %B     The full month name according to the current locale.

       %c     The preferred date and time representation for the current locale.

       %C     The century number (year/100) as a 2-digit integer. (SU)

       %d     The day of the month as a decimal number (range 01 to 31).

       %D     Equivalent to %m/%d/%y.  (Yecch--for Americans only.  Americans should note that in
	      other countries %d/%m/%y is rather common.  This means that in  international  con-
	      text this format is ambiguous and should not be used.) (SU)

       %e     Like  %d,  the day of the month as a decimal number, but a leading zero is replaced
	      by a space. (SU)

       %E     Modifier: use alternative format, see below. (SU)

       %F     Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)

       %G     The ISO 8601 week-based year (see NOTES) with century as	a  decimal  number.   The
	      4-digit year corresponding to the ISO week number (see %V).  This has the same for-
	      mat and value as %Y, except that if the ISO week number belongs to the previous  or
	      next year, that year is used instead. (TZ)

       %g     Like %G, but without century, that is, with a 2-digit year (00-99). (TZ)

       %h     Equivalent to %b.  (SU)

       %H     The hour as a decimal number using a 24-hour clock (range 00 to 23).

       %I     The hour as a decimal number using a 12-hour clock (range 01 to 12).

       %j     The day of the year as a decimal number (range 001 to 366).

       %k     The  hour  (24-hour  clock)  as a decimal number (range 0 to 23); single digits are
	      preceded by a blank.  (See also %H.)  (TZ)

       %l     The hour (12-hour clock) as a decimal number (range 1 to	12);  single  digits  are
	      preceded by a blank.  (See also %I.)  (TZ)

       %m     The month as a decimal number (range 01 to 12).

       %M     The minute as a decimal number (range 00 to 59).

       %n     A newline character. (SU)

       %O     Modifier: use alternative format, see below. (SU)

       %p     Either "AM" or "PM" according to the given time value, or the corresponding strings
	      for the current locale.  Noon is treated as "PM" and midnight as "AM".

       %P     Like %p but in lowercase: "am" or "pm" or a corresponding string	for  the  current
	      locale. (GNU)

       %r     The  time  in  a.m.  or  p.m.  notation.	In the POSIX locale this is equivalent to
	      %I:%M:%S %p.  (SU)

       %R     The time in 24-hour notation (%H:%M).  (SU) For a version  including  the  seconds,
	      see %T below.

       %s     The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). (TZ)

       %S     The  second  as a decimal number (range 00 to 60).  (The range is up to 60 to allow
	      for occasional leap seconds.)

       %t     A tab character. (SU)

       %T     The time in 24-hour notation (%H:%M:%S).	(SU)

       %u     The day of the week as a decimal, range 1 to 7, Monday being 1.  See also %w.  (SU)

       %U     The week number of the current year as a decimal number, range 00 to  53,  starting
	      with the first Sunday as the first day of week 01.  See also %V and %W.

       %V     The ISO 8601 week number (see NOTES) of the current year as a decimal number, range
	      01 to 53, where week 1 is the first week that has at least 4 days in the new  year.
	      See also %U and %W.  (SU)

       %w     The day of the week as a decimal, range 0 to 6, Sunday being 0.  See also %u.

       %W     The  week  number of the current year as a decimal number, range 00 to 53, starting
	      with the first Monday as the first day of week 01.

       %x     The preferred date representation for the current locale without the time.

       %X     The preferred time representation for the current locale without the date.

       %y     The year as a decimal number without a century (range 00 to 99).

       %Y     The year as a decimal number including the century.

       %z     The +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC).
	      (SU)

       %Z     The timezone name or abbreviation.

       %+     The date and time in   date(1)  format. (TZ) (Not supported in glibc2.)

       %%     A literal '%' character.

       Some conversion specifications can be modified by preceding the conversion specifier char-
       acter by the E or O modifier to indicate that an alternative format should  be  used.   If
       the  alternative format or specification does not exist for the current locale, the behav-
       ior will be as if the unmodified conversion specification were used. (SU) The Single  UNIX
       Specification  mentions	%Ec,  %EC, %Ex, %EX, %Ey, %EY, %Od, %Oe, %OH, %OI, %Om, %OM, %OS,
       %Ou, %OU, %OV, %Ow, %OW, %Oy, where the effect of the O modifier  is  to  use  alternative
       numeric	symbols  (say,	roman  numerals),  and that of the E modifier is to use a locale-
       dependent alternative representation.

       The broken-down time structure tm is defined in <time.h>.  See also   ctime(3) .

RETURN VALUE
       Provided that the result string, including the terminating null byte, does not exceed  max
       bytes, strftime() returns the number of bytes (excluding the terminating null byte) placed
       in the array s.	If the length of the result string (including the terminating null  byte)
       would exceed max bytes, then strftime() returns 0, and the contents of the array are unde-
       fined.  (This behavior applies since at least libc 4.4.4; very old versions of libc,  such
       as libc 4.4.1, would return max if the array was too small.)

       Note that the return value 0 does not necessarily indicate an error.  For example, in many
       locales %p yields an empty string.  An empty format string will likewise  yield	an  empty
       string.

ENVIRONMENT
       The environment variables TZ and LC_TIME are used.

CONFORMING TO
       SVr4,  C89, C99.  There are strict inclusions between the set of conversions given in ANSI
       C (unmarked), those given in the Single UNIX Specification (marked  SU),  those	given  in
       Olson's	timezone  package (marked TZ), and those given in glibc (marked GNU), except that
       %+ is not supported in glibc2.  On the other hand  glibc2  has  several	more  extensions.
       POSIX.1	only  refers  to  ANSI C; POSIX.2 describes under   date(1)  several extensions that
       could apply to strftime() as well.  The %F conversion is in C99 and POSIX.1-2001.

       In SUSv2, the %S specifier allowed a range of 00 to 61, to allow for the theoretical  pos-
       sibility  of  a	minute	that  included	a double leap second (there never has been such a
       minute).

NOTES
   ISO 8601 week dates
       %G, %g, and %V yield values calculated from the week-based year defined	by  the  ISO 8601
       standard.   In  this  system,  weeks  start on a Monday, and are numbered from 01, for the
       first week, up to 52 or 53, for the last week.  Week 1 is the first  week  where  four  or
       more  days  fall  within the new year (or, synonymously, week 01 is: the first week of the
       year that contains a Thursday; or, the week that has 4 January  in  it).   When	three  of
       fewer  days of the first calendar week of the new year fall within that year, then the ISO
       8601 week-based system counts those days as part of week 53 of the  preceding  year.   For
       example,  1  January  2010 is a Friday, meaning that just three days of that calendar week
       fall in 2010.  Thus, the ISO 8601 week-based system considers these days  to  be  part  of
       week 53 (%V) of the year 2009 (%G); week 01 of ISO 8601 year 2010 starts on Monday, 4 Jan-
       uary 2010.

   Glibc notes
       Glibc provides some extensions for conversion specifications.  (These extensions  are  not
       specified in POSIX.1-2001, but a few other systems provide similar features.)  Between the
       '%' character and the conversion specifier character, an optional flag and field width may
       be specified.  (These precede the E or O modifiers, if present.)

       The following flag characters are permitted:

       _      (underscore) Pad a numeric result string with spaces.

       -      (dash) Do not pad a numeric result string.

       0      Pad  a  numeric result string with zeros even if the conversion specifier character
	      uses space-padding by default.

       ^      Convert alphabetic characters in result string to upper case.

       #      Swap the case of the result string.  (This flag works only with certain  conversion
	      specifier characters, and of these, it is only really useful with %Z.)

       An optional decimal width specifier may follow the (possibly absent) flag.  If the natural
       size of the field is smaller than this width, then the result string  is  padded  (on  the
       left) to the specified width.

BUGS
       If  the	output string would exceed max bytes, errno is not set.  This makes it impossible
       to distinguish this error case from cases where the format string legitimately produces	a
       zero-length  output  string.   POSIX.1-2001  does not specify any errno settings for strf-
       time().

       Some buggy versions of   gcc(1)  complain about the use of %c: warning: `%c' yields only last
       2  digits  of  year  in	some locales.  Of course programmers are encouraged to use %c, it
       gives the preferred date and time representation.  One meets all kinds of strange obfusca-
       tions to circumvent this   gcc(1)  problem.  A relatively clean one is to add an intermediate
       function

	   size_t
	   my_strftime(char *s, size_t max, const char *fmt,
		       const struct tm *tm)
	   {
	       return strftime(s, max, fmt, tm);
	   }

       Nowadays,   gcc(1)  provides the -Wno-format-y2k option to prevent the warning, so	that  the
       above workaround is no longer required.

EXAMPLE
       RFC 2822-compliant date format (with an English locale for %a and %b)

	 "%a, %d %b %Y %T %z"

       RFC 822-compliant date format (with an English locale for %a and %b)

	 "%a, %d %b %y %T %z"

   Example program
       The program below can be used to experiment with strftime().

       Some  examples of the result string produced by the glibc implementation of strftime() are
       as follows:

	   $ ./a.out '%m'
	   Result string is "11"
	   $ ./a.out '%5m'
	   Result string is "00011"
	   $ ./a.out '%_5m'
	   Result string is "	11"

       Here's the program source:

       #include <time.h>
       #include <stdio.h>
       #include <stdlib.h>

       int
       main(int argc, char *argv[])
       {
	   char outstr[200];
	   time_t t;
	   struct tm *tmp;

	   t = time(NULL);
	   tmp = localtime(&t);
	   if (tmp == NULL) {
	       perror("localtime");
	       exit(EXIT_FAILURE);
	   }

	   if (strftime(outstr, sizeof(outstr), argv[1], tmp) == 0) {
	       fprintf(stderr, "strftime returned 0");
	       exit(EXIT_FAILURE);
	   }

	   printf("Result string is \"%s\"\n", outstr);
	   exit(EXIT_SUCCESS);
       }

SEE ALSO
         date(1) ,   time(2) ,   ctime(3) ,   setlocale(3) ,   sprintf(3) ,   strptime(3) 

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

GNU					    2013-06-28				        STRFTIME(3)
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