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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():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
The functions timelocal() and timegm() are the inverses of localtime(3) and gmtime(3). Both functions take a broken-down time and convert it to calendar time
(seconds since the Epoch, 1970-01-01 00:00:00 +0000, UTC). The difference between the two functions is that timelocal() takes the local timezone into account
when doing the conversion, while timegm() takes the input value to be Coordinated Universal Time (UTC).
RETURN VALUE
On success, these functions return the calendar time (seconds since the Epoch), expressed as a value of type time_t. On error, they return the value (time_t) -1
and set errno to indicate the error.
ERRORS
EOVERFLOW
The result cannot be represented.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬────────────────────┐
│Interface │ Attribute │ Value │
├───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼────────────────────┤
│timelocal(), timegm() │ Thread safety │ MT-Safe env locale │
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴────────────────────┘
CONFORMING TO
These functions are nonstandard GNU extensions that are also present on the BSDs. Avoid their use.
NOTES
The timelocal() function is equivalent to the POSIX standard function mktime(3). There is no reason to ever use it.
SEE ALSO
gmtime(3), localtime(3), mktime(3), tzset(3)
GNU 2021-03-22 TIMEGM(3)