The mktime function converts the broken-down time, expressed as local time, in the structure pointed to by timeptr into a calendar time with the same encoding as that of the values returned by the time function. The original values of the tm_wday and tm_yday components of the structure are ignored, and the original values of other components are not restricted to the ranges indicated above. On successful completion, the values of the tm_wday and tm_yday components of the structure are set appropriately, and the other components are set to represent the specified calendar time, but with their values forced to the ranges indicated above; the final value of tm_day is not set until tm_mon and tm_year are determined.