The system_localtime function is a thread-safe version of the standard localtime function. This function 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 might point to the data item represented by the second parameter, or the pointer might 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.