Yes, I have spent a lot of time there going thru the information on the web. I could have easily missed what I was looking for. I will have to go back thru it and read the compressed files with better scrutiny.
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 chuck.har...@thermofisher.com -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of John McKown Sent: Friday, June 27, 2014 9:26 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Local Time conversion to/from UTC Time On Fri, Jun 27, 2014 at 5:28 PM, Hardee, Chuck < chuck.har...@thermofisher.com> wrote: > 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 Have you looked at the IANA TimeZone Database? http://www.iana.org/time-zones Wikipedia entry: http://en.wikipedia.org/wiki/Tz_database That page has a compressed "text" file which contains a lot of TimeZone information. It is public domain. It is what GNU/Linux uses to adjust the local time from the UTC values. It has a _lot_ of data in it. It contains offsets for time zones and dates within that time zone (i.e. such as when the U.S. decided to change when to change to/from DST). Some Perl code at: http://search.cpan.org/dist/Date-Manip/lib/Date/Manip/TZdata.pod Unfortunately, I don't have any example code sitting around. Nor did I find any with a simple Google search. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
