Manpages - timegm.3

timegm, timelocal - inverses of gmtime and localtime

  #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

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).

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.

EOVERFLOW

The result cannot be represented.

For an explanation of the terms used in this section, see *attributes*(7).

These functions are nonstandard GNU extensions that are also present on the BSDs. Avoid their use.

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

*gmtime*(3), *localtime*(3), *mktime*(3), *tzset*(3)

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