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Linux 2.6 - man page for timelocal (linux section 3)

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

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

COLOPHON
       This page is part of release 3.55 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					    2013-07-04					TIMEGM(3)
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