However, I still contend that these cases are different. In the case of a field that goes beyond its normal range, you can clearly and unambiguously determine the user's intent, since mktime() was designed to make it easy to do something like calculate a date that is, say, 14 days in the future or past by simply adding or subtracting fourteen days on the tm_mday field. Then mktime() takes the denormalized representation and does the right thing.
I agree it is unambiguous if this is how a caller uses mktime(). However, a caller could simply set the tm structure and enter an invalid time. mktime() makes a guess/adjustment in those cases not knowing which direction caller wants to go. Jennifer ________________________________ From: Scott Atwood [mailto:scott.roy.atwood@gmail.com] Sent: Thursday, December 11, 2008 11:15 AM To: Paul Koning Cc: tz@lecserver.nci.nih.gov; tz@lecserver.nci.nih.gov Subject: Re: time during standard to DST transition On Thu, Dec 11, 2008 at 10:59 AM, Paul Koning <Paul_Koning@dell.com> wrote: >>>>> "Jennifer" == Jennifer Wang <(jennifwa)" <jennifwa@cisco.com>> writes: Jennifer> I think in most case when a caller sets the time to 2:10am Jennifer> Mar 8, 2009 in America/Los_Angeles, he does not realize Jennifer> it's the "missing hour". If he wants 1:10am (which is a Jennifer> valid time), he would use that. So moving forward to Jennifer> 3:10am seems to make sense. No, it doesn't. If he meant 3:10 he would have said so. There is no basis at all to guess at the user's intent in this way. It's very simple. The user is asking for a non-existent time. So the reject is valid. It is every bit as valid as an attempt to set the current date/time to February 30th. That's actually a poorly chosen example, since mktime() does guess the users intent in a case like that, by normalizing fields that are out of range. February 30th would be normalized to March 1st or March 2nd (depending on the year). However, I still contend that these cases are different. In the case of a field that goes beyond its normal range, you can clearly and unambiguously determine the user's intent, since mktime() was designed to make it easy to do something like calculate a date that is, say, 14 days in the future or past by simply adding or subtracting fourteen days on the tm_mday field. Then mktime() takes the denormalized representation and does the right thing. In the case of the non-existent hour during a DST transition, there is an inherent ambiguity, since you don't know if the caller added to or subtracted from the tm_hour field to get to the invalid time. -Scott -- Scott Atwood Cycle tracks will abound in Utopia. ~H.G. Wells