Std::localtime (3) Linux Manual Page

std::localtime – std::localtime

Synopsis

Defined in header<ctime>

    std::tm *localtime(const std::time_t *time);

Converts given time since epoch as std::time_t value into calendar time, expressed in local time.

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.
POSIX_specifies that the timezone information is determined by this function as if by calling tzset, which reads the environment variable TZ.

Example

// Run this code

#include <iostream>

#include <iomanip>

#include <ctime>

#include <stdlib.h> // defines putenv in POSIX
int main()

{
    std::time_t t = std::time(nullptr);
    std::cout << "UTC:       " << std::put_time(std::gmtime(&t), "%c %Z") << '\n';
    std::cout << "local:     " << std::put_time(std::localtime(&t), "%c %Z") << '\n';
    // POSIX-specific:
    std::string tz = "TZ=Asia/Singapore";
    putenv(tz.data());
    std::cout << "Singapore: " << std::put_time(std::localtime(&t), "%c %Z") << '\n';
}

Output:

  UTC: Fri Sep 15 14:16:29 2017 GMT
  local: Fri Sep 15 14:16:29 2017 UTC
  Singapore: Fri Sep 15 22:16:29 2017 SGT

std::localtime (3) Linux Manual Page