gmtime, gmtime_r, gmtime_s
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C
Concurrency support (C11)
Date and time utilities
Functions
Time manipulation
(C11)
(C23)
Format conversions
(deprecated in C23)(C11)
(deprecated in C23)(C11)
(C95)
gmtimegmtime_rgmtime_s
(C23)(C11)
(C23)(C11)
Constants
Types
(C11)
Defined in header
<time.h>
1) Converts given time since epoch (a time_t value pointed to by timer) 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 buf for the result.
3) Same as (1), except that the function uses user-provided storage buf for the result and that the following errors are detected at runtime and call the currently installed constraint handler function:
- timer or buf is a null pointer
- As with all bounds-checked functions,
gmtime_sis 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 constant 1 before including <time.h>.
[edit] Parameters
timer
-
pointer to a time_t object to convert
buf
-
pointer to a struct tm object to store the result
[edit] 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.2,3) copy of the buf pointer, or null pointer on error (which may be a runtime constraint violation or a failure to convert the specified time to UTC).
[edit] Notes
gmtime may not be thread-safe.
POSIX requires that gmtime and gmtime_r set errno to EOVERFLOW if they fail because the argument is too large.
The implementation of gmtime_s in Microsoft CRT is incompatible with the C standard since it has reversed parameter order.
[edit] Example
Run this code
#define __STDC_WANT_LIB_EXT1__ 1 #define _XOPEN_SOURCE // for putenv #include <stdio.h> #include <stdlib.h> // for putenv #include <time.h> int main(void) { time_t t = time (NULL ); printf ("UTC: %s", asctime (gmtime(&t))); printf ("local: %s", asctime (localtime (&t))); // POSIX-specific putenv("TZ=Asia/Singapore"); printf ("Singapore: %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 }
Possible output:
UTC: Fri Sep 15 14:22:05 2017 local: Fri Sep 15 14:22:05 2017 Singapore: Fri Sep 15 22:22:05 2017 UTC: Fri Sep 15 14:22:05 2017 local: Fri Sep 15 14:22:05 2017
[edit] References
- C23 standard (ISO/IEC 9899:2024):
- 7.27.3.3 The gmtime function (p: TBD)
- K.3.8.2.3 The gmtime_s function (p: TBD)
- C17 standard (ISO/IEC 9899:2018):
- 7.27.3.3 The gmtime function (p: 288)
- K.3.8.2.3 The gmtime_s function (p: 454-455)
- 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
[edit] See also
C++ documentation for gmtime