c/chrono/mktime

Renormalizes local calendar time expressed as a tm object and also converts it to time since epoch as a time_t object. and are ignored. The values in are not checked for being out of range.

A negative value of causes  to attempt to determine if Daylight Saving Time was in effect in the specified time.

If the conversion to is successful, the  object is modified. All fields of are updated to fit their proper ranges. and are recalculated using information available in other fields.

Return value
time since epoch as a time_t object on success, or if  cannot be represented as a time_t object (POSIX also requires  to be stored in errno in this case).