The system_localtime function is a thread-safe version of the standard localtime function. It returns the current time in the local time zone.
struct tm *system_localtime(const time_t *tp, const struct tm *res);
A pointer to a calendar time (tm) structure containing the local time. Depending on your system, the pointer may point to the data item represented by the second parameter, or it may point to a statically allocated item. For portability, do not assume either situation.
time_t *tp is an arithmetic time.
tm *res is a pointer to a calendar time (tm) structure.