Defined in header <time.h> | ||
---|---|---|
struct tm *gmtime( const time_t *time ); | (1) | |
struct tm *gmtime_s(const time_t *restrict time, struct tm *restrict result); | (2) | (since C11) |
1) Converts given time since epoch (a
time_t
value pointed to by time
) into calendar time, expressed in Coordinated Universal Time (UTC) in the struct tm format. The result is stored in static storage and a pointer to that static storage is returned. 2) Same as (1), except that the function uses user-provided storage
result
for the result and that the following errors are detected at runtime and call the currently installed constraint handler function: -
-
time
orresult
is a null pointer
-
- As with all bounds-checked functions,
gmtime_s
is only guaranteed to be available if__STDC_LIB_EXT1__
is defined by the implementation and if the user defines__STDC_WANT_LIB_EXT1__
to the integer constant1
before includingtime.h
.
Parameters
time | - | pointer to a time_t object to convert |
result | - | pointer to a struct tm object to store the result |
Return value
1) pointer to a static internal
tm
object on success, or null pointer otherwise. The structure may be shared between gmtime
, localtime
, and ctime
and may be overwritten on each invocation. 2) copy of the
result
pointer, or null pointer on error (which may be a runtime constraint violation or a failure to convert the specified time to UTC)Notes
This function gmtime
may not be thread-safe.
POSIX requires that this function sets errno
to EOVERFLOW
if it fails because the argument is too large.
POSIX defines a thread-safe alternative gmtime_r, which is similar to the C11 function gmtime_s
, except that it does not check the validity of its input parameters.
Example
#define __STDC_WANT_LIB_EXT1__ 1 #include <time.h> #include <stdio.h> int main(void) { time_t t = time(NULL); printf("UTC: %s", asctime(gmtime(&t))); printf("local: %s", asctime(localtime(&t))); #ifdef __STDC_LIB_EXT1__ struct tm buf; char str[26]; asctime_s(str,sizeof str,gmtime_s(&t, &buf)); printf("UTC: %s", str); asctime_s(str,sizeof str,localtime_s(&t, &buf))); printf("local: %s", str); #endif }
Output:
UTC: Tue Feb 17 18:12:09 2015 local: Tue Feb 17 13:12:09 2015 UTC: Tue Feb 17 18:12:09 2015 local: Tue Feb 17 13:12:09 2015
References
- C11 standard (ISO/IEC 9899:2011):
- 7.27.3.3 The gmtime function (p: 393-394)
- K.3.8.2.3 The gmtime_s function (p: 626-627)
- C99 standard (ISO/IEC 9899:1999):
- 7.23.3.3 The gmtime function (p: 343)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.12.3.3 The gmtime function
See also
(C11) | converts time since epoch to calendar time expressed as local time (function) |
C++ documentation for gmtime |
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