#include <time.h>struct tm *gmtime(const time_t *time);
The gmtime( ) function returns a pointer to the broken-down form of time in the form of a tm structure. The time is represented in Coordinated Universal Time (UTC), which is essentially Greenwich mean time. The time pointer is usually obtained through a call to time( ). If the system does not support Coordinated Universal Time, NULL is returned.
The structure used by gmtime( ) to hold the broken-down time is statically allocated and is overwritten each time the function is called. If you want to save the contents of the structure, you must copy it elsewhere.
Related functions are localtime( ), time( ), and asctime( ).