time_t time_utc;
struct tm tm_local;
// Get the UTC time
time(&time_utc);
// Get the local time
// Use localtime_r for threads safe
localtime_r(&time_utc, &tm_local);
time_t time_local;
struct tm tm_gmt;
// Change tm to time_t
time_local = mktime(&tm_local);
// Change it to GMT tm
gmtime_r(&time_utc, &tm_gmt);
int time_zone = tm_local.tm_hour - tm_gmt.tm_hour;
if (time_zone < -12) {
time_zone += 24;
} else if (time_zone > 12) {
time_zone -= 24;
}
注意必須聯網，否則無效