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Linux 2.6 - man page for strftime (linux section 3posix)

STRFTIME(P)			    POSIX Programmer's Manual			      STRFTIME(P)

NAME
       strftime - convert date and time to a string

SYNOPSIS
       #include <time.h>

       size_t strftime(char *restrict s, size_t maxsize,
	      const char *restrict format, const struct tm *restrict timeptr);

DESCRIPTION
       The  strftime() function shall place bytes into the array pointed to by s as controlled by
       the string pointed to by format. The format is a character string, beginning and ending in
       its  initial  shift  state,  if any. The format string consists of zero or more conversion
       specifications and ordinary characters.	A conversion  specification  consists  of  a  '%'
       character, possibly followed by an E or O modifier, and a terminating conversion specifier
       character that determines the conversion specification's behavior. All ordinary characters
       (including  the	terminating  null  byte)  are copied unchanged into the array. If copying
       takes place between objects that overlap, the behavior is undefined. No more than  maxsize
       bytes  are  placed  into  the  array. Each conversion specifier is replaced by appropriate
       characters as described in the following list. The appropriate characters  are  determined
       using the LC_TIME category of the current locale and by the values of zero or more members
       of the broken-down time structure pointed to by timeptr, as specified in brackets  in  the
       description.  If  any of the specified values are outside the normal range, the characters
       stored are unspecified.

       Local timezone information is used as though strftime() called tzset().

       The following conversion specifications are supported:

       %a     Replaced by the locale's abbreviated weekday name. [ tm_wday]

       %A     Replaced by the locale's full weekday name. [ tm_wday]

       %b     Replaced by the locale's abbreviated month name. [ tm_mon]

       %B     Replaced by the locale's full month name. [ tm_mon]

       %c     Replaced by the locale's appropriate date and time representation.  (See	the  Base
	      Definitions volume of IEEE Std 1003.1-2001, <time.h>.)

       %C     Replaced	by the year divided by 100 and truncated to an integer, as a decimal num-
	      ber [00,99]. [ tm_year]

       %d     Replaced by the day of the month as a decimal number [01,31]. [ tm_mday]

       %D     Equivalent to %m / %d / %y . [ tm_mon, tm_mday, tm_year]

       %e     Replaced by the day of the month as a decimal number [1,31]; a single digit is pre-
	      ceded by a space. [ tm_mday]

       %F     Equivalent  to  %Y  -  %m - %d (the ISO 8601:2000 standard date format). [ tm_year,
	      tm_mon, tm_mday]

       %g     Replaced by the last 2 digits of the week-based year (see below) as a decimal  num-
	      ber [00,99]. [ tm_year, tm_wday, tm_yday]

       %G     Replaced	by  the  week-based  year  (see  below) as a decimal number (for example,
	      1977). [ tm_year, tm_wday, tm_yday]

       %h     Equivalent to %b . [ tm_mon]

       %H     Replaced by the hour (24-hour clock) as a decimal number [00,23].  [ tm_hour]

       %I     Replaced by the hour (12-hour clock) as a decimal number [01,12].  [ tm_hour]

       %j     Replaced by the day of the year as a decimal number [001,366]. [ tm_yday]

       %m     Replaced by the month as a decimal number [01,12]. [ tm_mon]

       %M     Replaced by the minute as a decimal number [00,59]. [ tm_min]

       %n     Replaced by a <newline>.

       %p     Replaced by the locale's equivalent of either a.m. or p.m. [ tm_hour]

       %r     Replaced by the time in a.m. and p.m. notation;	 in the POSIX locale  this  shall
	      be equivalent to %I : %M : %S %p .  [ tm_hour, tm_min, tm_sec]

       %R     Replaced by the time in 24-hour notation ( %H : %M ).  [ tm_hour, tm_min]

       %S     Replaced by the second as a decimal number [00,60]. [ tm_sec]

       %t     Replaced by a <tab>.

       %T     Replaced by the time ( %H : %M : %S ). [ tm_hour, tm_min, tm_sec]

       %u     Replaced	by  the  weekday as a decimal number [1,7], with 1 representing Monday. [
	      tm_wday]

       %U     Replaced by the week number of the year as a decimal  number  [00,53].   The  first
	      Sunday  of January is the first day of week 1; days in the new year before this are
	      in week 0. [ tm_year, tm_wday, tm_yday]

       %V     Replaced by the week number of the year (Monday as the first day of the week) as	a
	      decimal  number  [01,53]. If the week containing 1 January has four or more days in
	      the new year, then it is considered week 1. Otherwise, it is the last week  of  the
	      previous year, and the next week is week 1. Both January 4th and the first Thursday
	      of January are always in week 1. [ tm_year, tm_wday, tm_yday]

       %w     Replaced by the weekday as a decimal number [0,6], with 0  representing  Sunday.	[
	      tm_wday]

       %W     Replaced	by  the  week  number of the year as a decimal number [00,53].	The first
	      Monday of January is the first day of week 1; days in the new year before this  are
	      in week 0. [ tm_year, tm_wday, tm_yday]

       %x     Replaced by the locale's appropriate date representation. (See the Base Definitions
	      volume of IEEE Std 1003.1-2001, <time.h>.)

       %X     Replaced by the locale's appropriate time representation. (See the Base Definitions
	      volume of IEEE Std 1003.1-2001, <time.h>.)

       %y     Replaced	by  the  last  two  digits  of	the  year as a decimal number [00,99].	[
	      tm_year]

       %Y     Replaced by the year as a decimal number (for example, 1997). [ tm_year]

       %z     Replaced by the offset from UTC in the ISO 8601:2000 standard  format  (	+hhmm  or
	      -hhmm  ),  or by no characters if no timezone is determinable. For example, "-0430"
	      means 4 hours 30 minutes behind UTC (west of Greenwich).	 If tm_isdst is zero, the
	      standard	time  offset is used. If tm_isdst is greater than zero, the daylight sav-
	      ings time offset is used. If tm_isdst is negative, no characters are  returned.	[
	      tm_isdst]

       %Z     Replaced by the timezone name or abbreviation, or by no bytes if no timezone infor-
	      mation exists. [ tm_isdst]

       %%     Replaced by % .

       If a conversion specification does not correspond to any of the	above,	the  behavior  is
       undefined.

       If  a  struct tm broken-down time structure is created by localtime() or localtime_r(), or
       modified by mktime(), and the value of TZ is subsequently modified, the results of the  %Z
       and %z strftime() conversion specifiers are undefined, when strftime() is called with such
       a broken-down time structure.

       If a struct  tm	broken-down  time  structure  is  created  or  modified  by  gmtime()  or
       gmtime_r(),  it	is  unspecified whether the result of the %Z and %z conversion specifiers
       shall refer to UTC or the current local timezone, when strftime() is called  with  such	a
       broken-down time structure.

   Modified Conversion Specifiers
       Some  conversion  specifiers can be modified by the E or O modifier characters to indicate
       that an alternative format or specification should be used rather than  the  one  normally
       used  by  the  unmodified conversion specifier. If the alternative format or specification
       does not exist for the  current	locale	(see  ERA  in  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001,  Section 7.3.5, LC_TIME), the behavior shall be as if the unmodified
       conversion specification were used.

       %Ec    Replaced by the locale's alternative appropriate date and time representation.

       %EC    Replaced by the name of the base year (period) in the locale's  alternative  repre-
	      sentation.

       %Ex    Replaced by the locale's alternative date representation.

       %EX    Replaced by the locale's alternative time representation.

       %Ey    Replaced by the offset from %EC (year only) in the locale's alternative representa-
	      tion.

       %EY    Replaced by the full alternative year representation.

       %Od    Replaced by the day of the month, using the locale's alternative	numeric  symbols,
	      filled  as  needed  with leading zeros if there is any alternative symbol for zero;
	      otherwise, with leading spaces.

       %Oe    Replaced by the day of the month, using the locale's alternative	numeric  symbols,
	      filled as needed with leading spaces.

       %OH    Replaced	by  the  hour (24-hour clock) using the locale's alternative numeric sym-
	      bols.

       %OI    Replaced by the hour (12-hour clock) using the locale's  alternative  numeric  sym-
	      bols.

       %Om    Replaced by the month using the locale's alternative numeric symbols.

       %OM    Replaced by the minutes using the locale's alternative numeric symbols.

       %OS    Replaced by the seconds using the locale's alternative numeric symbols.

       %Ou    Replaced	by  the  weekday  as  a number in the locale's alternative representation
	      (Monday=1).

       %OU    Replaced by the week number of the year (Sunday as the first day of the week, rules
	      corresponding to %U ) using the locale's alternative numeric symbols.

       %OV    Replaced by the week number of the year (Monday as the first day of the week, rules
	      corresponding to %V ) using the locale's alternative numeric symbols.

       %Ow    Replaced by the number of the weekday (Sunday=0)	using  the  locale's  alternative
	      numeric symbols.

       %OW    Replaced by the week number of the year (Monday as the first day of the week) using
	      the locale's alternative numeric symbols.

       %Oy    Replaced by the year (offset from %C ) using the locale's alternative numeric  sym-
	      bols.

       %g  ,  %G , and %V give values according to the ISO 8601:2000 standard week-based year. In
       this system, weeks begin on a Monday and week 1 of the year is the week that includes Jan-
       uary 4th, which is also the week that includes the first Thursday of the year, and is also
       the first week that contains at least four days in the year. If the first Monday of  Janu-
       ary is the 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding
       year; thus, for Saturday 2nd January 1999, %G is replaced by 1998 and %V  is  replaced  by
       53.   If  December  29th, 30th, or 31st is a Monday, it and any following days are part of
       week 1 of the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998
       and %V is replaced by 01.

       If a conversion specifier is not one of the above, the behavior is undefined.

RETURN VALUE
       If  the	total  number  of resulting bytes including the terminating null byte is not more
       than maxsize, strftime() shall return the number of bytes placed into the array pointed to
       by s, not including the terminating null byte. Otherwise, 0 shall be returned and the con-
       tents of the array are unspecified.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   Getting a Localized Date String
       The following example first sets the locale to the user's default.  The locale information
       will  be  used  in  the nl_langinfo() and strftime() functions. The nl_langinfo() function
       returns the localized date string which specifies how the date is laid out. The strftime()
       function  takes	this  information and, using the tm structure for values, places the date
       and time information into datestring.

	      #include <time.h>
	      #include <locale.h>
	      #include <langinfo.h>
	      ...
	      struct tm *tm;
	      char datestring[256];
	      ...
	      setlocale (LC_ALL, "");
	      ...
	      strftime (datestring, sizeof(datestring), nl_langinfo (D_T_FMT), tm);
	      ...

APPLICATION USAGE
       The range of values for %S is [00,60] rather than [00,59] to allow for the occasional leap
       second.

       Some of the conversion specifications are duplicates of others. They are included for com-
       patibility with nl_cxtime() and nl_ascxtime(), which were published in Issue 2.

       Applications should use %Y (4-digit years) in preference to %y (2-digit years).

       In the C locale, the E and O modifiers are ignored and the  replacement	strings  for  the
       following specifiers are:

       %a     The first three characters of %A .

       %A     One of Sunday, Monday, ..., Saturday.

       %b     The first three characters of %B .

       %B     One of January, February, ..., December.

       %c     Equivalent to %a %b %e %T %Y .

       %p     One of AM or PM.

       %r     Equivalent to %I : %M : %S %p .

       %x     Equivalent to %m / %d / %y .

       %X     Equivalent to %T .

       %Z     Implementation-defined.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       asctime() , clock() , ctime() , difftime() , getdate() , gmtime() , localtime() , mktime()
       ,  strptime()  ,  time()  ,   tzset()   ,   utime()   ,	 Base	Definitions   volume   of
       IEEE Std 1003.1-2001, Section 7.3.5, LC_TIME, <time.h>

COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      STRFTIME(P)


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