This article was previously published under Q39908
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The Microsoft time functions calculate for daylight saving time. Inparticular, mktime() will set the hour ahead or back one houraccording to the rules of daylight saving time. The only way to changethe dates that the time functions use in calculating daylight savingtime is to get the run-time library source code available for the timefunctions and modify the routine _isindst() in the file TZSET.C.