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).

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value
 | Thread safety | MT-Safe env locale

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
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