gmtime

gmtime

Converts a timer value into a year, month, day, hour, minute, second, etc.

 #include <time.h> struct tm *gmtime ( const time_t *timer  );

The gmtime( ) function converts a numeric time value (usually a number of seconds since January 1, 1970, but not necessarily) into the equivalent date and time structure in Coordinated Universal Time (UTC, formerly called Greenwich Mean Time; hence the function's name). To obtain similar values for the local time, use the function localtime( ).

The function's argument is not the number of seconds itself, but a pointer to that value. Both the structure type struct tm and the arithmetic type time_t are defined in the header file time.h.

The tm structure is defined as follows:

 struct tm {   int tm_sec;            /* Seconds since the full minute: 0 to 60 */   int tm_min;            /* Minutes since the full hour:   0 to 59 */   int tm_hour;           /* Hours since midnight:          0 to 23 */   int tm_mday;           /* Day of the month:     1 to  31 */   int tm_mon;            /* Months since January: 0 to  11 */   int tm_year;           /* Years since 1900               */   int tm_wday;           /* Days since Sunday:    0 to   6 */   int tm_yday;           /* Days since Jan. 1:    0 to 365 */   int tm_isdst;          /* Flag for Daylight Savings Time:                             greater than 0 if time is DST;                             equal to 0 if time is not DST;                             less than 0 if unknown.        */ };

The argument most often passed to gmtime( ) is the current time, obtained as a number with type time_t by calling the function time( ). The type time_t is usually defined as a time.h as equivalent to long or unsigned long.

Example

The following program prints a string showing the offset of the local time zone from UTC:

 time_t     rawtime; struct tm  utc_tm, local_tm, *ptr_tm; char       buffer[1024] = ""; time( &rawtime );                        // Get current time as an integer. ptr_tm = gmtime( &rawtime );             // Convert to UTC in a struct tm. memcpy( &utc_tm, ptr_tm, sizeof(struct tm) );   // Save a local copy. ptr_tm = localtime( &rawtime );          // Do the same for local time zone. memcpy( &local_tm, ptr_tm, sizeof(struct tm) ); if ( strftime( buffer, sizeof(buffer),                "It's %A, %B %d, %Y, %R o'clock, UTC.", &utc_tm ) )   puts( buffer ); if ( strftime( buffer, sizeof(buffer),                "Here it's %A, %B %d, %Y, %R o'clock, UTC %z.", &local_tm ) )   puts( buffer );

This code produces the following output:

 It's Tuesday, March 22, 2005, 22:26 o'clock, UTC. Here it's Wednesday, March 23, 2005, 00:26 o'clock, UTC +0200.

Example

See Also