struct tm *gmtime_r(time_t *timep, struct tm *result)

Home » c » time » gmtime_r

struct tm *gmtime_r(time_t *timep, struct tm *result)

The gmtime_r() is similar to gmtime(), but stores data in user supplied struct.

Examples

1. current time around the world
2. use gmtime_r() in a multithreading enviroment

current time around the world   return

program.c   copy

#include <stdio.h>
#include <time.h>

void print_time( struct tm * tm , const char *location, int zone)
{
    int hour;

    hour = (24 + tm ->tm_hour + zone) % 24;
    printf ( "%20s: %02d:%02d\n" , location, hour, tm ->tm_min);
}

// Mountain Standard Time (MST) is 7 hours behind Coordinated Universal Time.
#define MST -7

// Greenwich Mean Time (GMT) has no offset from Coordinated Universal Time.
#define GMT 0

// China Standard Time (CST) is 8 hours ahead of Coordinated Universal Time.
#define CST 8

int main()
{
    time_t now;
    struct tm tm ;

    now = time (NULL);
    // convert 'struct tm' to 'time_t'
    gmtime_r(&now, & tm );

    print_time(& tm , "Phoenix, USA" , MST);
    print_time(& tm , "London, England" , GMT);
    print_time(& tm , "Beijing, China" , CST);
    return 0;
}

Output

   Phoenix, USA: 05:38
London, England: 12:38
 Beijing, China: 20:38

use gmtime_r() in a multithreading enviroment   return

program.c   copy

#include <stdio.h>
#include <pthread.h>
#include <time.h>
#include <unistd.h>

void print_time()
{
    time_t now;
    struct tm tm ;
    char buffer[64];

    now = time (NULL);
    gmtime_r(&now, & tm );
    asctime_r(& tm , buffer);
    printf ( "UTC time = %s" , buffer);
}

void *routine( void *arg)
{
    int i;

    for (i = 0; i < 2; i++) {
        print_time();
        sleep(1);
    }
    return NULL;
}

int main()
{
    int i;
    pthread_t tid;

    pthread_create(&tid, NULL, routine, NULL);
    routine(NULL);
    pthread_join(tid, NULL);
    return 0;
}

Output

?

1 2 3 4

UTC time = Fri Jan 2 12:43:08 2015 UTC time = Fri Jan 2 12:43:08 2015 UTC time = Fri Jan 2 12:43:09 2015 UTC time = Fri Jan 2 12:43:09 2015