All the Timezone in Windows are displayed in such a way like
(GMT+10:00) Canberra, Melbourne, Sydney,
GMT and Offset and the place. In turn , the Linux is having every timezone as directory mapping in /usr/share/zoneinfo/[Continent]/[Place].
I am in need of mapping every Windows timezone to the Linux timezone for my application.
like
(GMT+05:30) Chennai, Kolkata, Mumbai, New Delhi => Asia/Calcutta
Now the problem surface for the International Date Line West which lies between Russia and America. In Windows, its marked by (GMT-12:00) International Date Line West and from various sources I found that in Linux its Etc/GMT+12.
(GMT-12:00) International Date Line West => Etc/GMT+12
also
(GMT+12:00) Coordinated Universal Time+12 => Etc/GMT-12
(GMT-02:00) Coordinated Universal Time-02 => Etc/GMT+2
(GMT-11:00) Coordinated Universal Time-11 => Etc/GMT+11
This keeps me puzzled and my app works closely with the Timestamp w.r.t UTC and the UTC offset. So this mapping is confusing me and the app.
Can anyone explain why there is a vice versa of -12 and +12 Offset in both for a same place?
Thanks in Advance :)
Unicode.org hosts a mapping as part of the CLDR. You can get to the latest version here. There are also XML versions of the data linked from that page.
You can find example code (in Python) of how to generate a mapping from the XML data here.
Obligatory Time Zone Rant:
Note that whoever implemented the timezone support in Windows was on drugs. I'm not kidding you. Look at the timezone names. Why is Central European time known as "Romance standard Time". Romance? What, because it includes Paris, or? Roman Standard Time could have made sense a it also includes Rome, but Romance!?
Also, in the registry the timezones are not organized under their id. No, they are, insanely, organized under their display name! Since that is localized, it means every timezone will be located under a different key in different translations of Windows!!! So to find the right timezone, you have to look through all the timezone to see which has the correct id.
I have example code of that too here. See the get_win_timezone() function.
I wonder if it is the same guy who designed this that decided that POSIX should reverse the sign on timezones, so that -8 hours mean plus 8 hours. In any case, I'm sure they were smoking something illegal together.
If all the files have the signs reversed, then the files you are looking at are forward mapping offsets, while what you are probably more familiar with is reverse mapping offsets.
Windows typically uses the local timezone for the machine's internal time, so it needs timezone files which can translate back to UTC. Linux typically uses UTC as the machine's internal time, so it needs timezone files which can translate to local time.
Since the offsets for the two machines describe complimentary but opposite directions of time, it stands to reason that the time zone files are inversely related to each other. In other words, if you pick up a set of zone files from one, the other set will be negative.
The definitions in the Etc directory are meant to be POSIX style, thus they have their sign reversed from what you would expect. I'm not an expert for POSIX, but as far as I get it, the basic idea was to express timzones by the combination of their local name and the offset to GMT. An example for middle europe (Central European Time / CET):
Europe/Berlin (w/o daylight savings) equals GMT+01:00 equals CET-1
GMT-1 in the Etc directory in fact describes a (fictous) timezone called "GMT" which is one hour ahead of (the real) GMT.
As far as I know, these files are only there to allow you to create (symbolic) links against them, so if you were situated somwhere in middle europe, you would create a link to GMT-1 and call it CET-1.
The best recommendation I can give you is to entirely ignore the Etc directory and use some mapping table from windows timezone names to unix timezone folders/files. Windows timezone info does not only give the offset to GMT, but also knows about Daylight Savings (and when in begins or ends). The same is true for the folders/files in the timezone database, but not for the files in the Etc directory - they give a simple static offset to GMT.
A list of time zones in the tz database can be found in the wikipedia.
Related
Seems easy but I didn't find a way to convert an UTC datetime to a specified timezone. I found how to convert an UTC date time to local date-time, but now I want to convert to a specific timezone (i.e. for example Moscow time)
For example in c# we can do:
// user-specified time zone
TimeZoneInfo southPole =
TimeZoneInfo.FindSystemTimeZoneById("Antarctica/South Pole Standard Time");
// an UTC DateTime
DateTime utcTime = new DateTime(2007, 07, 12, 06, 32, 00, DateTimeKind.Utc);
// DateTime with offset
DateTimeOffset dateAndOffset =
new DateTimeOffset(utcTime, southPole.GetUtcOffset(utcTime));
Console.WriteLine(dateAndOffset);
But how to do in Delphi ?
A few things:
"Antarctica/South Pole Standard Time" isn't a real time zone identifier. I assume you gave that in jest, but it makes it unclear as to whether you want to use Windows time zone identifiers (like "Eastern Standard Time"), or IANA time zone identifiers (like "America/New_York").
Assuming you want to use Windows identifiers, you can indeed use the functions in the Win32 API. The comment in the question suggested the wrong API however. You should instead use SystemTimeToTzSpecificLocalTimeEx.
It uses the DYNAMIC_TIME_ZONE_INFORMATION structure, which have been available since Windows Vista. To get one of those from a named Windows time zone identifier, use the EnumDynamicTimeZoneInformation function to loop through the system time zones until you find the one matching on the TimeZoneKeyName field.
The "dynamic" structures are important to use, and should always be preferred over their older counterparts. They allow access to changes in time zones and daylight saving time rules that are stored in the Windows registry. Without them, you only get access to the current rule, which might not be the correct rule for the date you are converting.
If you instead wanted to use IANA time zone identifiers, use the Delphi tzdb library, as shown in this post.
If you are uncertain of which to use, I highly recommend this approach. IANA identifiers are inter-operable with other operating systems, programming languages, frameworks, and libraries. (Windows identifiers, less so.)
In some cases, the bot may have knowledge of the user's timezone. Is there a way to pass this knowledge to the bot framework so that it can handle certain date forms correctly - e.g. "tomorrow" & "yesterday"? Even things like "next friday" are sometimes sensitive to the timezone.
Currently, it appears that these are handled assuming the user's timezone offset is zero.
It seems that the chronic parser is unreachable so you can't really change anything to that. I see 3 solutions.
Solution 1: Create your own RecognizeDateTime class to work with utc time or however you want.
Solutions 2: When you get the date (in the validation method for example) add the utc offset to the time. This will preserve the right date, for utc times and local times.
dateTime += TimeZone.CurrentTimeZone.GetUtcOffset(dateTime);
solution 3: When the datetime is created by using a string like "yesterday", the day is correct but the time defaults to 00:00 or 12AM. To make this less sensitive you can just add 12 hours to the UTC time. This will preserve the day in almost all timezones. (All timezones above 12+ will have a problem. Luckily there aren't many people there.) (This is the solution I'm currently using for one of my solutions)
Perhaps this question should be broken up into two posts, but I currently have an API for a few business customers. I am currently using ISO 8601 timestamps with a UTC time zone to represent times. However, I don't like the idea of these timestamps being attached to any timezone because the times should be the same no matter what timezone you are in. 5PM UTC should be 5PM CST, etc...
I know that you can leave the Z off of an ISO timestamp, and it will be interpreted as whatever local time you are in. Is this ok practice? And if so, how do I do this in Ruby? I read the doc for the Time class and didn't see anything about this.
EDIT: Let me re-word this just a little bit, or atleast clarify something. The reason why I'm seeking timestamps that aren't attached to a timezone is exactly because I know that my client servers and API server will hardly ever match up. If a client is submitting an event with a time, that time needs to be ambiguously equal to the ambiguous locale specific to the event that the user is working on.
That's a mouthful...assume that I'm working on an event scheduler. Each event belongs to a storefront or location of a company. When times are being shown for a location, it is assumed that the times shown are in the timezone of the location, and for clarity's sake should never be shown at a time formatted to a user's local timezone. If I'm looking at the scheduler on the East Coast, but looking at events for locations on the West Coast, the times I should see should be local to the locations on the West Coast, not adjusted for my timezone.
I know a solution could be to simply store times with timezone information for the location its associated to. But the use case that a user would want to convert a time to their timezone is VERY rare, and I'd rather make implementing my API easier...this was actually my original implementation but implementing the API in many different environments and across multiple programming languages, it became clear that it is a hurdle to show times local to that timestamp's timezone for a lot of languages. If a user wanted to convert times to their local timezone I could easily store global timezone information for the location object itself.
I don't know what you mean by "the times should be the same no matter what timezone you are in. 5PM UTC should be 5PM CST, etc..". 5PM UTC clearly isn't 5PM CST!
Anyway, I don't think that what you are proposing is an ok practice. Suppose you leave off the Z and have a timestamp be interpreted as whatever local time you are in. Since this is a network API, the client and server might not be in the same timezone. When the client submits a "local" time, what does it mean? The local time on the client (if so, how does the server know what that is?)? The local time on the server? It's ambiguous. This is the crux of the reason why just about the only reasonable thing to do is to use UTC throughout.
What you can do is attach a timezone to a timestamp if it might be relevant. For example, "you should observe one minute of silence at 2012-11-10T22:00:00Z in honour of the soldiers who died in WW1" sounds weird because Rememberance Day isn't on November 10! "you should observe one minute of silence at 2012-11-11T11:00:00+13:00" sounds a lot better once you put that New Zealand time zone in there... In this case you can keep and timestamp (in either local or UTC) together with the timezone offset (e.g. store both of them together in your database).
It does, however, depend on what your times represent. For example, in "at equinoxes, sunset happens at 18:00" it makes sense to use an abstract time that isn't qualified with a timezone (it's true in every timezone, and/or you're talking about solar time). But attaching a date to this abstract time makes little sense, so I don't think you would be talking about ISO8601 in this case.
I have released an app which,. within its functionality displays date and time strings.
I am aware of the differing formats across cultures - however in some cases I had hardcoded values- for example I had gone with a custom format that was the 12 hr clock and showed AM/PM
I am now changing to use the standard date time format strings where possible, and so, for my times,I am now using the shortTimePattern.
What has surprised me is that for the US this shows as say 3:15PM but in the UK its 16:15 i.e the default there is the 24 hr clock.
Similarly in the US the long date includes the day of the week, where as in the UK it does not.
I am thinking that these defaults must be right and are what is expected within that country but is this really the case? I had no idea that the UK default would be a 24 hr clock. And, for those users in the UK who have the app, will they be annoyed when the next update shows the time in this format?
Interested in any opinions around this.
thanks
UK Users will not care between 24hr and am/pm (we don't talk to each other saying "It's fourteen hundred o'clock :P).
Dates are also fine unless you're using format of 12/02/12 as in the UK that's considered 12th Feb whereas in the states it's December 2nd.
This is not the place to solicit "opinions" on whether the behaviour provided by the framework is correct.
Assume that the framework is correct, unless you know otherwise.
If you want to know what your users will think you should ask them. (I assume that your users are not typical users of StackOverflow.) If you don't already have beta users in your target markets to ask then make the change to use the "standard" behaviour. If there is a problem your users will tell you.
Is thee some way of implementing a custom time zone in windows?
We have some PCs in Creston, British Columbia, Canada (Time zone exception) which stays the same time all year. So essentially, Creston does not observe a time zone. Can I implement this behavior in windowsÉ
I wrote a lengthy blog post about a similar problem we had: http://subjectivecoder.blogspot.com.au/2013/04/creating-custom-windows-timezones.html
The short version is that there is a spot in the registry which allows you to modify or create new time zones - but the registry format is fairly nasty.
Microsoft has a GUI tool called TZEdit which you can find here: http://support.microsoft.com/kb/914387 (scroll down to Method 2 and download TZEdit.exe).
If you want to see what's going on behind the scenes, I've published the source to the command line tool I built here: https://github.com/Rophuine/TimeZoneInfoGenerator (it's untested and quick-and-dirty but may help you understand what's going on, if you're interested).
Apart from daylight savings time, this is normal MST (UTC-0700), right?
Windows used to have a checkbox called something like "Automatically adjust the clock for daylight savings time". Maybe you can hunt that down. Even if there is no checkbox, chances are that the registry setting still exists.
The data is in: HKLM\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Time zones.
You can probably add your own zone.
Each zone has its own key. And they contain a lot of data. Some zones have a subkey Dynamic DST.
This is not exactly an answer, but you might consider trying to get Creston recognized as an official time zone. As for how exactly to do that... contact Microsoft, I guess, and ask where they get their time zone info from. Probably the closest thing to an official time zone database in computer programming is zoneinfo but I'm not sure if Microsoft uses it.
WARNING: You should be very careful about creating your own time zone, even if you think your systems are isolated.
This could cause problems with exchanging information with other systems, both from conversion errors as well as exception handling.
If the time zone you want is legally recognized, you should consider bothering your vendor to properly add you to the time zone repository they use.