No, that is fundamentally impossible.

Suppose I give you the date '27 October 2002, 2:30', and the timezone is CET. Is that in daylight savings time or not? The answer is that *both* are possible. There will be a 27 October 2002, 2:30 in DST, followed one hour later by a 27 October 2002, 2:30 not in DST.

Of course it's possible that given a date (and time), and the timezone to calculate which date/times have to be DST, which ones cannot be DST, which ones can be both (typically just one hour/year), and which date/time combinations are impossible (typically one hour/year as well). After all, that's what your computer does too when displaying time ;-) But the rules differ from timezone to timezone.

Note that in your particular example, with TZ = MST7MDT, it's easy, as then the timezone name itself indicates daylight savings time is active.

I don't understand your steps to determine DST though. With step 1, you convert the date to epoch seconds - but you already need to know the timezone and whether it's DST or not for that. And why are you in step 3 fiddling with the epoch?

Finally, did you study Time::Local and see how that tackles the problem?

Abigail

In reply to Re: Determining Daylight Savings Time by Abigail-II
in thread Determining Daylight Savings Time by Starky

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