path: root/missing_d/strftime.3

STRFTIME(3)                          Library Functions Manual                         STRFTIME(3)

NAME
       strftime - generate formatted time information

SYNOPSIS
       #include <sys/types.h>
       #include <time.h>

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

DESCRIPTION
       The following description is transcribed verbatim from the January 18, 1999 draft standard
       for ISO C.  This draft is essentially identical in technical content to the final  version
       of the standard.

       ``The  strftime function places characters into the array pointed to by s as controlled by
       the string pointed to by format.  The format shall be a multibyte character sequence,  be-
       ginning and ending in its initial shift state.  The format string consists of zero or more
       conversion specifiers and ordinary multibyte characters.  A conversion specifier  consists
       of  a  %  character,  possibly followed by an E or O modifier character (described below),
       followed by a character that determines the behavior of the conversion specifier.  All or-
       dinary  multibyte  characters  (including  the  terminating null character) are copied un-
       changed into the array.  If copying takes place between objects that overlap the  behavior
       is undefined.  No more than maxsize characters are placed into the array.

       ``Each conversion specifier is replaced by appropriate characters as described in the fol-
       lowing list.  The appropriate characters are determined by 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 by brackets in the description.  If any of the  speci-
       fied values is outside the normal range, the characters stored are unspecified.''

       %a     is replaced by the locale's abbreviated weekday name.

       %A     is replaced by the locale's full weekday name.

       %b     is replaced by the locale's abbreviated month name.

       %B     is replaced by the locale's full month name.

       %c     is  replaced by the locale's appropriate date and time representation.  (This is %A
              %B %d %T %Y in the "C" locale.)

       %C     is replaced by the year divided by 100 and truncated to an integer,  as  a  decimal
              number (00-99).

       %d     is replaced by the day of the month as a decimal number (01-31).

       %D     is equivalent to %m/%d/%y.

       %e     is  replaced  by the day of the month as a decimal number (1-31); a single digit is
              preceded by a space.

       %F     is equivalent to %Y-%m-%d (the ISO 8601 date format).

       %g     is replaced by the year without century of the ISO week number as a decimal  number
              (00-99).

       %G     is replaced by the year with century of the ISO week number as a decimal number.

       %h     is equivalent to %b.

       %H     is replaced by the hour (24-hour clock) as a decimal number (00-23).

       %I     is replaced by the hour (12-hour clock) as a decimal number (01-12).

       %j     is replaced by the day of the year as a decimal number (001-366).

       %m     is replaced by the month as a decimal number (01-12).

       %M     is replaced by the minute as a decimal number (00-59).

       %n     is replaced with a newline character (ASCII LF).

       %p     is  replaced by the locale's equivalent of the AM/PM designations associated with a
              12-hour clock.

       %r     is replaced by the locale's 12-hour clock time.  (This is %I:%M:%S %p  in  the  "C"
              locale.)

       %R     is equivalent to %H:%M.

       %S     is replaced by the second as a decimal number (00-60).

       %t     is replaced with a TAB character.

       %T     is equivalent to %H:%M:%S.

       %u     is replaced by the ISO 8601 weekday as a decimal number [1 (Monday)-7].

       %U     is  replaced  by  the week number of the year (the first Sunday as the first day of
              week 1) as a decimal number (00-53).

       %V     is replaced by the ISO 8601 week number of the year (the first Monday as the  first
              day of week 1) as a decimal number (01-53).

       %w     is replaced by the weekday as a decimal number [0 (Sunday)-6].

       %W     is  replaced  by  the week number of the year (the first Monday as the first day of
              week 1) as a decimal number (00-53).

       %x     is replaced by the locale's appropriate date representation.  (This is %A %B %d  %Y
              in the "C" locale.)

       %X     is  replaced  by  the locale's appropriate time representation.  (This is %T in the
              "C" locale.)

       %y     is replaced by the year without century as a decimal number (00-99).

       %Y     is replaced by the year with century as a decimal number.

       %z     The timezone offset in a  +HHMM  format  (e.g.  the  format  necessary  to  produce
              RFC-822/RFC-1036 date headers).

       %Z     is  replaced  by the time zone name or abbreviation, or by no characters if no time
              zone is determinable.

       %%     is replaced by %.

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

RETURNS
       If the total number of resulting characters including the terminating  null  character  is
       not  more than maxsize, the strftime function returns the number of characters placed into
       the array pointed to by s not including the terminating null character.   Otherwise,  zero
       is returned and the contents of the array are indeterminate.

ISO 8601
       The  method  for determining the week number as specified by ISO 8601 is: if the week con-
       taining January 1 has four or more days in the new year, then it is week 1,  otherwise  it
       is  the highest numbered week of the previous year (52 or 53) and the next week is week 1.
       All days in a new year preceding the first Monday are considered to be in week 0.

       For example, January 1, 1993, is in week 53 of 1992. Thus, the year of its ISO week number
       is  1992,  even  though  its  year is 1993.  Similarly, December 31, 1973, is in week 1 of
       1974. Thus, the year of its ISO week number is 1974, even though its year is 1973.

ALTERNATE REPRESENTATIONS
       The alternate representations %Ec, %EC, %Ex, %EX, %Ey, %EY, %Od, %Oe, %OH, %OI, %Om,  %OM,
       %OS, %Ou, %OU, %OV, %Ow, %OW, and %Oy are recognized, but their normal representations are
       used.

NON-ISO EXTENSIONS
   SunOS Extensions
       If SUNOS_EXT is defined when the routine is compiled, then the following  additional  con-
       versions will be available.  These are borrowed from the SunOS version of strftime.

       %k     is  replaced  by the hour (24-hour clock) as a decimal number (0-23).  Single digit
              numbers are padded with a blank.

       %l     is replaced by the hour (12-hour clock) as a decimal number (1-12).   Single  digit
              numbers are padded with a blank.

   HP/UX Extensions
       If HPUX_EXT is defined when the routine is compiled, then the following additional conver-
       sions will be available.  These are borrowed from the HP-UX version of date.

       %N     The ``Emporer/Era'' name.  Typically, this is equivalent to the century (same as %C
              ).

       %o     The ``Emporer/Era'' year.  Typically, this is equivalent to the year (same as %y ).

   VMS Extensions
       If VMS_EXT is defined, then the following additional conversion is available:

       %v     The date in VMS format (e.g. 20-JUN-1991).

   Other Extensions
       If HAVE_MKTIME is defined, then this conversion is available:

       %s     The time in ``seconds since the Epoch,'' usually Midnight January 1, 1970, UTC.

SEE ALSO
       time(2), ctime(3), localtime(3), mktime(3), tzset(3)

BUGS
       This  version  does not handle multibyte characters or pay attention to the setting of the
       LC_TIME environment variable.

       The ``appropriate'' values used for %c, %x, are %X are always those specified by the  1999
       ISO C standard for the "C" locale.

CAVEATS
       The  pre-processor  symbol POSIX_SEMANTICS is automatically defined, which forces the code
       to call tzset(3) whenever the TZ environment variable has changed.  If this  routine  will
       be used in an application that will not be changing TZ, then there may be some performance
       improvements by not defining POSIX_SEMANTICS.

AUTHOR
       Arnold Robbins <arnold@skeeve.com>

ACKNOWLEDGEMENTS
       Thanks to Geoff Clare <gwc@root.co.uk> for helping debug earlier versions of this routine,
       and   for  advice  about  POSIX  semantics.   Additional  thanks  to  Arthur  David  Olsen
       <ado@elsie.nci.nih.gov>  for  some  code  improvements.   Thanks  also  to  Tor  Lillqvist
       <tml@tik.vtt.fi>  for  code fixes to the ISO 8601 code.  Thanks to Hume Smith for pointing
       out a problem with the ISO 8601 code and to Arthur David Olsen for further discussions.

                                                                                      STRFTIME(3)