C code to get local time offset in minutes relative to UTC?

Question

I didn\'t find a trivial way to get the time offset in minutes between the local time and the UTC time.

At first I intended to use tzset() but it doesn\'t p

Answer 1

IMHO the only foolproof and portable way is to use localtime and gmtime and manually compute the delta in minute because those 2 functions exist on all known systems. For example:

int deltam() {
    time_t t = time(NULL);
    struct tm *loc = localtime(&t);
    /* save values because they could be erased by the call to gmtime */
    int loc_min = loc->tm_min;
    int loc_hour = loc->tm_hour;
    int loc_day = loc->tm_mday;
    struct tm *utc = gmtime(&t);
    int delta = loc_min - utc->tm_min;
    int deltaj = loc_day - utc->tm_mday;
    delta += (loc_hour - utc->tm_hour) * 60;
    /* hack for the day because the difference actually is only 0, 1 or -1 */
    if ((deltaj == 1) || (deltaj < -1)) {
        delta += 1440;
    }
    else if ((deltaj == -1) || (deltaj > 1)) {
        delta -= 1440;
    }
    return delta;
}

Beware, I did not test all possible corner cases, but it could be a starting point for your requirement.