Tim, Thanks for these pointers to the 'how-to' and zdump.c. I'll read the how-to when I get a free moment, and maybe also try to compile zdump.c for MS-DOS, to see how it works. I fear it might not translate easily to an Arduino environment, though! The other issue I have with the results you've listed is that they are using absolute dates rather than quoting the official rules (e.g. 'first Sunday in October', 'first Sunday in April', etc). This would be fine as long as my clock has access to the TZdb each year, but what if the database someday ceases to exist (or be maintained)? Unlikely though that is, I would nevertheless like to be able to, in that unthinkable circumstance, continue adjusting DST for the user's locale, based on the actual rules and calculating my own dates each year. Regards, Daniel ________________________________ From: Tim Parenti [mailto:tim@timtimeonline.com] Sent: Sunday, October 15, 2017 11:22 AM To: Daniel Ford Cc: Time Zone Mailing List Subject: Re: [tz] Beginner's help request Daniel, Just a short message to help you get quickly started along the right path. A guide to interpreting the source data can be found in tz-how-to.html; I'm not sure offhand whether that's in the particular tar file you have, but a development version is available from https://github.com/eggert/tz/blob/master/tz-how-to.html <https://github.com/eggert/tz/blob/master/tz-how-to.html> For your idea of a text-only table of already-parsed data, you may consider the zdump utility that is packaged in the distribution. For your example, to obtain the offsets for Australia/Hobart for 2017 only: $ zdump -vc 2017,2018 Australia/Hobart Australia/Hobart -9223372036854775808 = NULL Australia/Hobart -9223372036854689408 = NULL Australia/Hobart Sat Apr 1 15:59:59 2017 UTC = Sun Apr 2 02:59:59 2017 AEDT isdst=1 gmtoff=39600 Australia/Hobart Sat Apr 1 16:00:00 2017 UTC = Sun Apr 2 02:00:00 2017 AEST isdst=0 gmtoff=36000 Australia/Hobart Sat Sep 30 15:59:59 2017 UTC = Sun Oct 1 01:59:59 2017 AEST isdst=0 gmtoff=36000 Australia/Hobart Sat Sep 30 16:00:00 2017 UTC = Sun Oct 1 03:00:00 2017 AEDT isdst=1 gmtoff=39600 Australia/Hobart 9223372036854689407 = NULL Australia/Hobart 9223372036854775807 = NULL -- Tim Parenti sent from my Android phone On 14 Oct 2017 19:15, "Daniel Ford" <dfnojunk@gmail.com> wrote: I'm looking to develop a 'world clock' that could be sold to anyone (with Internet access via a Wi-Fi AP) anywhere in the world, that will display their local time, taking into account DST if/when applicable. Given that DST 'rules' can change at the whim of governments, my firmware will need to annually look up 'current' DST rules from the web. After much searching, it seems that your TZ Database is the best supported such reference for time zone rules. But I'm having great difficulty working out how I might access its mine of information... (I'll understand if you don't have time to help out a beginner, and maybe then you could refer me to a help site for TZ database applications.) I'm a hardware engineer with some programming experience, particularly assembler (various MCUs) and some C, but little or no experience in other languages. I'm developing this clock on an Arduino-like platform (NodeMCU, which has in-built Wi-Fi). My development tools run on a Win7Pro64 PC. The tools that you kindly provide for your database appear to be geared primarily towards Linux/Unix platforms, and I have no idea how I might convert them for a NodeMCU! I'm looking for some 'simple' way to access the desired TZ/DST information, preferably using simple string searches. For my application, all I'm interested in are the *current* rules. The wealth of history in your db is undoubtedly of interest to many, but for me is just 'clutter' to be searched through. But writing a program to find those rules for a particular locality has me stumped right now. I can't expect my dumb users to know a letter code for their time-zone/DST-rules, so all I'm expecting them to select from program-generated lists are: (1) their world region (Europe, Asia, Australasia, etc), and (2) the name of a major city in their time-zone with the same DST rules they follow. Let's take a concrete example: say my user has nominated 'Australasia' and 'Hobart'. So I look in your Australasia file and do a (manual at this stage) search for 'Hobart', but find only one reference to it (other than in comments). The jumble of numbers and letters there do not (clearly) tell me when DTS starts or ends. So how could I possibly write some code to find out that required information?? I've looked through the TZ_database-2017b.tar file for some sort of 'how-to' explanation of what all the file contents mean and how to programmatically search for a specific TZ, but have so far found nothing. Ideally, what I'd like to see is a text-only table of just current TZ/DST rules for each region/locality (they could all fit into a single file with all the historical data and comments removed), perhaps in the clear form used by Jack Christensen in his excellent Arduino Timezone library examples, such as... // Australia Eastern Time Zone (Sydney, Melbourne, Hobart) TimeChangeRule aEDT = {"AEDT", First, Sun, Oct, 2, 660}; TimeChangeRule aEST = {"AEST", First, Sun, Apr, 3, 600}; TimezoneExt ausET("NSW, Vic, Tas", aEDT, aEST); // Australia Eastern Time Zone (Brisbane) TimezoneExt QldT("Queensland", aEST, aEST); // no DST in Qld! ... which clearly tells me in a program-searchable way that in the main eastern states DST starts on the first Sunday in October at 2am, becoming UTC offset +11 hours (660 minutes), and ends on the first Sunday in April at 3am, reverting to UTC offset +10 hours. Couldn't be simpler! Any help in using the TZ database will be much appreciated (and acknowledged in my source code). Regards, Daniel --------------- Daniel Ford (Gerroa, Australia) "My loathings are simple: stupidity, oppression, crime, cruelty, soft music." - Vladimir Nabokov