# std::gmtime

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< cpp‎ | chrono‎ | c

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).

### Parameters

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.

### Notes

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.

### Example

Run this code

    #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

localtime | converts time since epoch to calendar time expressed as local time (function)

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