C Language: gmtime function
(Convert to Greenwich Mean Time)
In the C Programming Language, the gmtime function converts a calendar time (pointed to by timer) and returns a pointer to a structure containing a UTC (or Greenwich Mean Time) value.
Syntax
The syntax for the gmtime function in the C Language is:
struct tm *gmtime(const time_t *timer);
Parameters or Arguments
- timer
- A pointer to an object of type time_t that contains a time value to convert.
Returns
The gmtime function returns a pointer to a structure containing a UTC (Greenwich Mean Time) value describing a local time pointed to by timer.
Required Header
In the C Language, the required header for the gmtime function is:
#include <time.h>
Applies To
In the C Language, the gmtime function can be used in the following versions:
- ANSI/ISO 9899-1990
gmtime Example
Let's look at an example to see how you would use the gmtime function in a C program:
/* Example using gmtime by TechOnTheNet.com */
#include <stdio.h>
#include <time.h>
#define PDT (-7)
int main(int argc, const char * argv[])
{
/* Define temporary variables */
struct tm *gtime;
time_t now;
/* Read the current system time */
time(&now);
/* Convert the system time to GMT (now UTC) */
gtime = gmtime(&now);
/* Display the time in PDT and UTC */
printf ("Pacific Daylight Time: %2d:%02d\n", (gtime->tm_hour + PDT) % 24, gtime->tm_min);
printf ("Universal Time: %2d:%02d\n", gtime->tm_hour % 24, gtime->tm_min);
return 0;
}
When compiled and run, this application will output the current time in both the Pacific Daylight and Universal timezones. When we ran the application at 2:14PM, the output was the following:
Pacific Daylight Time: 14:14 Universal Time: 21:14
Similar Functions
Other C functions that are similar to the gmtime function:
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