8.7 mktime—convert time to arithmetic representation

Synopsis

#include <time.h>
time_t mktime(struct tm *timp);

Description
mktime assumes the time at timp is a local time, and converts its representation from the traditional representation defined by struct tm into a representation suitable for arithmetic.

localtime is the inverse of mktime.

Returns
If the contents of the structure at timp do not form a valid calendar time representation, the result is -1. Otherwise, the result is the time, converted to a time_t value.

Portability
ANSI C requires mktime.

mktime requires no supporting OS subroutines.