linux man page for timegm

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

NAME
       timegm, timelocal - inverses of gmtime and localtime

SYNOPSIS
       #include <time.h>

       time_t timelocal(struct tm *tm);

       time_t timegm(struct tm *tm);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       timelocal(), timegm(): _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       The functions timelocal() and timegm() are the inverses of localtime(3) and gmtime(3).

CONFORMING TO
       These functions are nonstandard GNU extensions that are also present on the BSDs.  Avoid their use; see NOTES.

NOTES
       The timelocal() function is equivalent to the POSIX standard function mktime(3).  There is no reason to ever use it.

       For a portable version of timegm(), set the TZ environment variable to UTC, call mktime(3) and restore the value of TZ.	Something like

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

	   time_t
	   my_timegm(struct tm *tm)
	   {
	       time_t ret;
	       char *tz;

	       tz = getenv("TZ");
	       setenv("TZ", "", 1);
	       tzset();
	       ret = mktime(tm);
	       if (tz)
		   setenv("TZ", tz, 1);
	       else
		   unsetenv("TZ");
	       tzset();
	       return ret;
	   }

SEE ALSO
       gmtime(3), localtime(3), mktime(3), tzset(3)

COLOPHON
       This  page is part of release 3.27 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
								    2007-07-26								 TIMEGM(3)