std::gmtime, std::gmtime_r

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

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Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

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Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

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Symbols index

External libraries

 

Date and time library

Time point time_point (C++11) clock_time_conversion (C++20)   clock_cast (C++20) Duration duration (C++11) Clocks system_clock (C++11) steady_clock (C++11) is_clock (C++20) utc_clock (C++20) tai_clock (C++20) high_resolution_clock (C++11) gps_clock (C++20) file_clock (C++20) local_t (C++20) Time of day is_amis_pm (C++20)(C++20) make12make24 (C++20)(C++20) hh_mm_ss (C++20)

Calendar day (C++20) month (C++20) year (C++20) weekday (C++20) operator/ (C++20) year_month_day (C++20) year_month_day_last (C++20) year_month_weekday (C++20) year_month_weekday_last (C++20)   weekday_indexed (C++20) weekday_last (C++20) month_day (C++20) month_day_last (C++20) month_weekday (C++20) month_weekday_last (C++20) year_month (C++20) last_speclast (C++20)(C++20) chrono I/O parse (C++20)

Time zone tzdb (C++20) tzdb_list (C++20) get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)(C++20)(C++20)(C++20) sys_info (C++20) local_info (C++20) nonexistent_local_time (C++20) ambiguous_local_time (C++20) locate_zone (C++20) current_zone (C++20) time_zone (C++20) choose (C++20) zoned_traits (C++20) zoned_time (C++20) time_zone_link (C++20) leap_second (C++20) leap_second_info (C++20) get_leap_second_info (C++20) C-style date and time

 

C-style date and time utilities

Functions

Time manipulation

difftime

time

clock

timespec_get (C++17)

timespec_getres (C++26)

Format conversions

asctime (deprecated in C++26)

ctime (deprecated in C++26)

strftime

wcsftime

gmtimegmtime_r (C++26)

localtimelocaltime_r (C++26)

mktime

timegm (C++26)

Constants

CLOCKS_PER_SEC

Types

tm

time_t

clock_t

timespec (C++17)

 

Defined in header <ctime>
std::tm* gmtime ( const std::time_t* time );	(1)
std::tm* gmtime_r( const std::time_t* time, std::tm* buf );	(2)	(since C++26)

Converts given time since epoch as std::time_t value into calendar time, expressed in Coordinated Universal Time (UTC).

1) Upon successfull conversion, the result is stored in an internal std::tm object shared between std::gmtime, std::localtime, and std::ctime and may be overwritten on each invocation.

If the returned pointer is accessed after the thread that called std::gmtime that returned it has exited, the behavior is undefined.

(since C++11)

2) Upon successfull conversion, the result is stored in the std::tm object pointed to by buf.

Parameters

time

-

pointer to a std::time_t object to convert

Return value

1) A pointer to the shared internal std::tm object on success, or a null pointer on error.

2) buf on success, or a null pointer on error.

Notes

std::gmtime may not be thread-safe.

(since C++11)

POSIX requires that this function sets errno to EOVERFLOW if it fails because the argument is too large.

Example

Run this code

#include <ctime>
#include <iomanip>
#include <iostream>
#include <sstream>
 
int main()
{
    setenv("TZ", "/usr/share/zoneinfo/Europe/London", 1); // POSIX-specific
    
    std::tm tm{}; // get_time does not set all fields hence {}
    tm.tm_year = 2020 - 1900; // 2020
    tm.tm_mon = 7 - 1; // July
    tm.tm_mday = 15; // 15th
    tm.tm_hour = 10;
    tm.tm_min = 15;
    tm.tm_isdst = 1; // Daylight saving in London
    std::time_t t = std::mktime(&tm); 
    
    std::cout << "UTC:   " << std::put_time(std::gmtime(&t), "%c %Z") << '\n';
    std::cout << "local: " << std::put_time(std::localtime(&t), "%c %Z") << '\n';
}

Possible output:

UTC:   Wed Jul 15 09:15:00 2020 GMT
local: Wed Jul 15 10:15:00 2020 BST

See also

localtimelocaltime_r (C++26)	converts time since epoch to calendar time expressed as local time (function)
C documentation for gmtime