John, I am in the process of writing a program that is reading several files. Some of the files have dates in local and some have dates in UTC. I want to be able to move between the two time bases as needed. I don't envision the program reading files from differing time zones at the same time, but the program could be reading files from any country in the world. Currently I'm concentrating on the US so a US based solution would be fine for the moment.
Where I can't seem to get my head to go is related to Daylight Savings Time (DST). If, for instance, the locale is the east coast of the US, the UTC adjustment would be -05:00, 05:00 UTC is 00:00 local. If the local time is 02:00 on the day of the switch in the spring, that's easy, subtract the signed UTC adjustment from the local time and then add 1 hour. So, 02:00 - (-05:00) - 01:00 = 06:00 UTC. But, what if the local time is 01:59? One would subtract the signed UTC adjustment from the local time and then??? So, 01:59 - (-05:00) = 06:59, but what about Daylight Savings Time? The current local time being adjusted is not with the DST range, but the adjusted time via the UTC adjustment value is. Does DST come into play here? Is the decision based on the local time or the resulting UTC time? A similar question comes into play on the other end of the DST range. If the local time is prior to the end of the DST range, does one subtract 1 hour from the adjusted time? Finally, what about the other direction. If one has a UTC time value, what are the rules governing the change to a local time with respect to DST? I hope my explanation isn't too simplistic. Any thoughts or direction might have that would help would be greatly appreciated. That also goes to anyone else that might have some input. Thanks, Chuck Charles (Chuck) Hardee Senior Systems Engineer/Database Administration CCG Information Technology Thermo Fisher Scientific 300 Industry Drive Pittsburgh, PA 15275 Direct: 724-517-2633 FAX: 412-490-9230 [email protected] -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of John Gilmore Sent: Friday, June 27, 2014 3:22 PM To: [email protected] Subject: Re: Local Time conversion to/from UTC Time Do you need a point solution, i.e., one for a particular longitude and latitude? Or dxo you need a general one that is parametric in location? John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
