rstepanov

Больше ада:

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

int main() {

    time_t t;
    struct tm tm1;

    tzset();
    time(&t);
    localtime_r(&t, &tm1);

    tm1.tm_mday = 27;
    tm1.tm_sec = 59;
    tm1.tm_min = 59;
    tm1.tm_hour = 0;
    tm1.tm_mon = 9;

    t = mktime(&tm1);
    printf(" tm_hour = %d:\t\t(%d) %s", tm1.tm_hour, t, asctime(&tm1));

    tm1.tm_mday = 26;
    tm1.tm_sec = 59;
    tm1.tm_min = 59;
    tm1.tm_hour = 0;
    tm1.tm_mon = 9;

    t = mktime(&tm1);
    printf(" tm_hour = %d:\t\t(%d) %s", tm1.tm_hour, t, asctime(&tm1));
}

Результат:
./tzcheck3
tm_hour = 0: (1414360799) Mon Oct 27 00:59:59 2014
tm_hour = 1: (1414274399) Sun Oct 26 01:59:59 2014