linux c 获取系统当前时区

#include<stdio.h>
#include<time.h>

int main()
{

     unsigned int timezone = 0;
     time_t t1, t2 ;
     struct tm *tm_local, *tm_utc;

	time(&t1);
	t2 = t1;
	printf("t1=%ul,t2=%ul\n", t1, t2);
	
	tm_local = localtime(&t1);
	printf("localtime=%d:%d:%d\n", tm_local->tm_hour, tm_local->tm_min, tm_local->tm_sec);
	t1 = mktime(tm_local) ;
	tm_utc = gmtime(&t2);
	printf("utcutctime=%d:%d:%d\n", tm_utc->tm_hour, tm_utc->tm_min, tm_utc->tm_sec);
	t2 = mktime(tm_utc);
	printf("***\n");
	printf("t1=%ul\nt2=%ul\n", t1, t2);
	
    timezone = (t1 - t2) / 3600;
	printf("%d\n", timezone);

	return 0;
}