c - How to known which time zone the system is using -

i'm doing code need known time zone active in system (i'm working on linux so):

• my first aproach check tz enviroment var,it's empty unless set (for instance calling tzset)

• after try extern long timezone (time.h) variable 0.

• finally calculate difference of timezone , utc+0 don't real timezone because don't known if daylight saving apply

i'm pretty sure there easy (and consistent) way achieve this. i'm looking "europe/paris" or "utc+2" or that

any appreciated!

as starting point, suggest this:

#include <stdio.h> #include <stdlib.h> #include <time.h>  int main(void) {   char str[64];   time_t timer;   struct tm * ptm;   timer = time(null);   ptm = localtime(&timer);    strftime(str, sizeof(str), "%z", ptm);   printf("tz: %s\n", str);   return(0); }