As others have implied, the reason you have not gotten a simple answer is that there is not simple answer. It's a nasty problem. Local time does what JCL and Hoover vacuum cleaners do.
It is particularly nasty for historical times as opposed to times "right around now" because the dates and geographies of DST have changed from year to year. As Gil pointed out, but you may have missed given the volume of replies, a complete solution is in fact impossible. Given a New York local time of 1:30am on the Sunday of the Fall DST change, what is the corresponding UTC time? It is impossible to know without knowing "which 1:30 am?" -- the one before setting the clocks back, or the one after? I don't understand your question about "when adjusted for UTC falls within the DST period." UTC has no DST. A time adjusted or converted to UTC never has a further DST adjustment applied. Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Hardee, Chuck Sent: Saturday, June 28, 2014 11:54 AM To: [email protected] Subject: Re: Local Time conversion to/from UTC Time Doesn't help, sorry. Given all the answers I've had so far, all pointing to things implying real-time conversion of timestamps, I think it is clear that I haven't stated my need very well. I have two (currently) sets of data. The data is historical. I have no control on how the data is produced, it's from a vendor product which shall remain nameless and is irrelevant. In the previous version of the product, both sets of data were saved with local times. In the current product, one set is saved in UTC, the other in local. The next version will save both sets of data in UTC. That being said, I need to be able to convert to and from local times and UTC times. And, let me say now, when I say "time", I mean a timestamp consisting of yyyy/mm/dd hh:mm:ss.tttttt, that is year, month, day, hour, minutes, seconds and microseconds. I currently have routines to determine the range of Daylight Savings Time, or as some of indicated, Summer Time, and other names, all boiling down to the same thing. I have a mechanism to obtain the offset to UTC as a signed value indicating before or after UTC, for example. On the East Coast of the US, the UTC offset is -5 hours (non-DST) and -4 hours (DST), meaning behind UTC. The issue becomes when I have a local time that falls outside of the DST period but when adjusted for UTC falls within the DST period. Does it get adjusted? For example, given a time of 01:59:59.999999 on the day of the switch to DST, when the UTC adjustment is made (assuming my US East Coast example), the time would be 06:59.59.999999. Now, the local time was outside the DST range, but when adjusted to UTC it falls within the DST range. Does the adjusted UTC time get adjusted for DST? And then, having gone thru the narration for local to UTC, a similar questions exists for UTC to local, and then similar questions regarding the other end of the DST period. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
