Date Time

Time, Date, and Localization Functions

The time and date functions are defined in the header time.h. This header defines three time-related types: clock_t, time_t, and tm.

The types clock_t and time_t represent the system time and date. This is called the calendar time.

Time structure

The tm structure contains the following members:

int tm_sec;  /* seconds, 0-60 */
int tm_min;  /* minutes, 0-59 */
int tm_hour; /* hours, 0-23 */
int tm_mday; /* day of the month, 1-31 */
int tm_mon;  /* months since Jan, 0-11 */
int tm_year; /* years from 1900 */
int tm_wday; /* days since Sunday, 0-6 */
int tm_yday; /* days since Jan 1, 0-365 */
int tm_isdst /* Daylight Saving Time indicator */

tm_isdst is positive during daylight saving time, zero if it not, and negative if there is no information available.

This form of the time and date is called the broken-down time.

In addition, time.h defines the macro CLOCKS_PER_SEC, which is the number of system clock ticks per second.

The geopolitical environmental functions require the header locale.h. It defines the structure lconv, which is described under the function localeconv().