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



NAME
       strftime - format date and time

SYNOPSIS
       #include 

       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 specification format and places the result in the  character
       array s of size max.

       Ordinary characters placed in the format string are copied to s without
       conversion.  Conversion specifications are introduced by a '%'  charac-
       ter,  and  terminated  by  a  conversion	 specifier  character, and are
       replaced in s 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 context this format is ambigu-
	      ous 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 deci-
	      mal number.  The 4-digit year corresponding to the ISO week num-
	      ber  (see %V).  This has the same format 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 includ-
	      ing the seconds, see %T below.

       %s     The number of seconds since the Epoch, that is, since 1970-01-01
	      00:00:00 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  time-zone  as  hour	offset	from  GMT.   Required  to emit
	      RFC 822-conformant  dates	 (using	  "%a, %d %b %Y %H:%M:%S %z").
	      (GNU)

       %Z     The timezone or 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 conver-
       sion  specifier	character  by  the E or O modifier to indicate that an
       alternative format should be used.  If the alternative format or speci-
       fication does not exist for the current locale, the behavior 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 .  See also
       ctime(3).

RETURN VALUE
       The strftime() function returns the number of characters placed in  the
       array  s, not including the terminating null byte, provided the string,
       including the terminating null byte, fits.  Otherwise,  it  returns  0,
       and  the	 contents  of  the array is undefined.	(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.

ENVIRONMENT
       The environment variables TZ and LC_TIME are used.

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

       In  SUSv2,  the	%S specifier allowed a range of 00 to 61, to allow for
       the theoretical possibility 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 Thursday, 4 January 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 conver-
       sion specifier character, an optional flag and field width may be spec-
       ified.  (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 only works  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
       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 pro-
       grammers are encouraged to use %c, it gives the preferred date and time
       representation.	One meets all kinds of strange obfuscations to circum-
       vent this gcc(1) problem.  A relatively clean one is to add an interme-
       diate 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
       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"

   Program source

       #include 
       #include 
       #include 

       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);
       } /* main */

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

COLOPHON
       This page is part of release 3.22 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				  2009-02-24			   STRFTIME(3)