gmtime, gmtime64 - Convert date and time to UTC

Definition	#include <time.h> struct tm *gmtime(const time_t *sec_p); struct tm *gmtime64(const time64_t *sec_p); gmtime and gmtime64 interpret the time specification to which sec_p points as the number of seconds which have passed since the reference date (epoch). The functions calculate the date and time from this and store the result in a structure of the type tm. If the POSIX "linkage option" library has been linked with preference, the result is stored in UTC (Universal Time Coordinated) format, otherwise as local time. Negative values are interpreted as seconds before the reference date. The earliest displayable date with gmtime is 12/13/1901 20:45:52 local time and 01/01/1900 00:00:00 with gmtime64. The latest date which can be displayed with gmtime is 01/19/2038 03:14:07 and 3/18/4317 02:44:48 with gmtime64. Warning If the POSIX "linkage option" library has not been linked with preference, it is not possible to get the result in UTC format. In this case gmtime and gmtime64 correspond to the localtime and localtime64 functions, each supplying the local time.
Return val.	Pointer to the calculated structure. gmtime and gmtime64 store the result in a structure declared in <time.h> as follows:
		struct tm { int tm_sec; /* seconds (0-59) */ int tm_min; /* minutes (0-59) */ int tm_hour; /* hours (0-23) */ int tm_mday; /* day of the month (1-31) */ int tm_mon; /* month from the start of the year (0-11) */ int tm_year; /* years since 1900 */ int tm_wday; /* weekday (0-6, 0=Sunday) */ int tm_yday; /* days since January 1 (0-365) */ int tm_isdst; /* daylight saving time flag */ };
	NULL	In the event of an error
Notes	The asctime, ctime, ctime64, gmtime, gmtime64, localtime and localtime64 functions write their result into the same internal C data area. This means that each of these function calls overwrites the previous result of any of the other functions.
Example	#include <time.h> #include <stdio.h> struct tm *t; char *s; time_t clk; int main(void) {  clk = time((time_t *)0);   t = gmtime(&clk);  printf("Year: %d\n", t->tm_year + 1900);  printf("Time in hours: %d\n", t->tm_hour);  printf("Day of the year: %d\n", t->tm_yday);  s = asctime(t);   printf("%s", s);  return 0; }
See also	asctime, ctime, ctime64, localtime, localtime6