C library function - gmtime()



The C library function struct tm *gmtime(const time_t *timer) uses the value pointed by timer to fill a tm structure with the values that represent the corresponding time, expressed in Coordinated Universal Time (UTC) or GMT timezone.


Following is the declaration for gmtime() function.

struct tm *gmtime(const time_t *timer)


  • timeptr -- This is the pointer to a time_t value representing a calendar time.

Return Value

This function returns pointer to a tm structure with the time information filled in. Below is the detail of timeptr structure:

struct tm {
   int tm_sec;         /* seconds,  range 0 to 59          */
   int tm_min;         /* minutes, range 0 to 59           */
   int tm_hour;        /* hours, range 0 to 23             */
   int tm_mday;        /* day of the month, range 1 to 31  */
   int tm_mon;         /* month, range 0 to 11             */
   int tm_year;        /* The number of years since 1900   */
   int tm_wday;        /* day of the week, range 0 to 6    */
   int tm_yday;        /* day in the year, range 0 to 365  */
   int tm_isdst;       /* daylight saving time             */	


The following example shows the usage of gmtime() function.

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

#define BST (+1)
#define CCT (+8)

int main ()

   time_t rawtime;
   struct tm *info;

   /* Get GMT time */
   info = gmtime(&rawtime );
   printf("Current world clock:\n");
   printf("London : %2d:%02d\n", (info->tm_hour+BST)%24, info->tm_min);
   printf("China  : %2d:%02d\n", (info->tm_hour+CCT)%24, info->tm_min);


Let us compile and run the above program, this will produce the following result:

Current world clock:
London : 14:10
China : 21:10