This is a Hardware specific function. It is not implemented in the Compiler.
#include <string.h>
time_t mktime(struct tm *time);
mktime() converts *time to a time_t. The fields of *time may have any value; they are not restricted to the ranges given time.h. If the conversion was successful, mktime() restricts the fields of *time to these ranges and also sets the tm_wday and tm_yday fields correctly.
*time as a time_t.
gmtime(), and