gmtime, _gmtime32, _gmtime64

Converts a time_t time value to a tm structure. More secure versions of these functions are available; see gmtime_s, _gmtime32_s, _gmtime64_s.


struct tm *gmtime( const time_t *sourceTime );
struct tm *_gmtime32( const __time32_t *sourceTime );
struct tm *_gmtime64( const __time64_t *sourceTime );


Pointer to the stored time. The time is represented as seconds elapsed since midnight (00:00:00), January 1, 1970, coordinated universal time (UTC).

Return value

A pointer to a structure of type tm. The fields of the returned structure hold the evaluated value of the sourceTime argument in UTC rather than in local time. Each of the structure fields is of type int, as follows:

Field Description
tm_sec Seconds after minute (0 - 59).
tm_min Minutes after hour (0 - 59).
tm_hour Hours since midnight (0 - 23).
tm_mday Day of month (1 - 31).
tm_mon Month (0 - 11; January = 0).
tm_year Year (current year minus 1900).
tm_wday Day of week (0 - 6; Sunday = 0).
tm_yday Day of year (0 - 365; January 1 = 0).
tm_isdst Always 0 for gmtime.

Both the 32-bit and 64-bit versions of gmtime, mktime, mkgmtime, and localtime all use one common tm structure per thread for the conversion. Each call to one of these functions destroys the result of any previous call. If sourceTime represents a date before midnight, January 1, 1970, gmtime returns NULL. There's no error return.

_gmtime64, which uses the __time64_t structure, enables dates to be expressed up through 23:59:59, December 31, 3000, UTC. _gmtime32 only represent dates through 23:59:59 January 18, 2038, UTC. Midnight, January 1, 1970, is the lower bound of the date range for both functions.

gmtime is an inline function that evaluates to _gmtime64, and time_t is equivalent to __time64_t unless _USE_32BIT_TIME_T is defined. If you must force the compiler to interpret time_t as the old 32-bit time_t, you can define _USE_32BIT_TIME_T, but doing so causes gmtime to be in-lined to _gmtime32 and time_t to be defined as __time32_t. We don't recommend use of _USE_32BIT_TIME_T, because it isn't allowed on 64-bit platforms. In any case, your application may fail after January 18, 2038.

These functions validate their parameters. If sourceTime is a NULL pointer, or if the sourceTime value is negative, these functions invoke an invalid parameter handler, as described in Parameter validation. If execution is allowed to continue, the functions return NULL and set errno to EINVAL.


The _gmtime32 function breaks down the sourceTime value and stores it in a statically allocated structure of type tm, defined in TIME.H. The value of sourceTime is typically obtained from a call to the time function.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.


Routine Required C header Required C++ header
gmtime, _gmtime32, _gmtime64 <time.h> <ctime> or <time.h>

For more compatibility information, see Compatibility.


// crt_gmtime.c
// compile with: /W3
// This program uses _gmtime64 to convert a long-
// integer representation of coordinated universal time
// to a structure named newtime, then uses asctime to
// convert this structure to an output string.

#include <time.h>
#include <stdio.h>

int main(void)
   struct tm *newtime;
   __int64 ltime;
   char buff[80];

   _time64( &ltime );

   // Obtain coordinated universal time:
   newtime = _gmtime64( &ltime ); // C4996
   // Note: _gmtime64 is deprecated; consider using _gmtime64_s
   asctime_s( buff, sizeof(buff), newtime );
   printf( "Coordinated universal time is %s\n", buff );
Coordinated universal time is Tue Feb 12 23:11:31 2002

See also

Time management
asctime, _wasctime
ctime, _ctime32, _ctime64, _wctime, _wctime32, _wctime64
_ftime, _ftime32, _ftime64
gmtime_s, _gmtime32_s, _gmtime64_s
localtime, _localtime32, _localtime64
_mkgmtime, _mkgmtime32, _mkgmtime64
mktime, _mktime32, _mktime64
time, _time32, _time64