mktime()

(gdb) p *start
$1 = {tm_sec = 0, tm_min = 25, tm_hour = 3, tm_mday = 20, tm_mon = 3,
tm_year = 3920, tm_wday = 5, tm_yday = 52, tm_isdst = 0, tm_gmtoff =
7200, tm_zone = 0x484b28b1 "EET"}
(gdb) n
138             tend = mktime(end);
(gdb) p tstart
$2 = -1
(gdb) p *start
$3 = {tm_sec = 0, tm_min = 25, tm_hour = 3, tm_mday = 20, tm_mon = 3,
tm_year = 3920, tm_wday = 5, tm_yday = 52, tm_isdst = 0, tm_gmtoff = 7200,
tm_zone = 0x484b28b1 "EET"}
(gdb)