Defined in header <ctime>
std::tm* gmtime( const std::time_t* time );

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


time - pointer to a time_t object to convert

Return value

Pointer to a static internal std::tm object on success, or null pointer otherwise. The structure may be shared between std::gmtime, std::localtime, and std::ctime and may be overwritten on each invocation.


This function may not be thread-safe.

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


#include <iostream>
#include <sstream>
#include <iomanip>
#include <ctime>
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

converts time since epoch to calendar time expressed as local time
C documentation for gmtime

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.