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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 specification	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 charac-
       ter sequences are ordinary character sequences.

       The  characters	of  ordinary  character	 sequences (including the null
       byte) are copied	verbatim 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 lo-
	      cale.

       %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 in-
	      cluding 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 conver-
       sion specifier character	by the E or O modifier to indicate that	an al-
       ternative format	should be used.	 If the	alternative format or specifi-
       cation 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 nu-
       merals),	and that of the	E modifier is to use a locale-dependent	alter-
       native 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  (ex-
       cluding	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 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.	 An empty for-
       mat 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 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 Monday, 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 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 strftime().

       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
       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 3.53 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)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | CONFORMING TO | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON

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