time_t mk_gmtime(const struct tm *timeptr)
This function 'compiles' the elements of a broken-down time structure, returning a binary time stamp. The elements of timeptr are interpreted as representing UTC.
The original values of the tm_wday and tm_yday elements of the structure are ignored, and the original values of the other elements are not restricted to the ranges stated for struct tm.
Unlike mktime(), this function DOES NOT modify the elements of timeptr.