The problem: converting a given string representing a date and time to a UTC time.

Time zones are funny things, annoyingly complicated and frustrating to program with. Obviously there are solutions and workarounds, mainly working with UTC (Universal Time Code - which is the same as GMT (Greenwich Mean Time) and WET (Western European Time) and I'm sure another 100 or so others!).

For those who are taking their first steps into the minefield of time zones in .NET they might be lulled into a false sense of security with the 'TimeZone' class available to developers. It seems promising, hell, a whole class called TimeZone! Easy money - surely something like:

Or something like:

But no, we unfortunately don't have this capability built in. It's a bit annoying, as we know the hosting O/S of the framework (be it *nix or Windows) knows the TimeZone conversion information, we've all played with the clock once or twice in the past and seen the world displayed with all its zones.

So, with the framework leaving us high and dry, what can we do? Firstly – looking around the interweb for time zone related information takes us on a tour of many sites dedicated to the world’s time zones, such as ‘The World Clock’, ‘World Time Zone’ and the ‘Time Zone Converter’ sites – generally just information providers – useful for finding out times etc, but not too practical for the programmatical (I’m pretty certain that isn’t a word) approach.

Then a bit of delving takes us to the Zoneinfo page (also known as TZ), a public domain database containing the relevant time zone information. Now we’re getting somewhere. It has an impressive amount of implementations, from the GNU C Library, to Mac OS X, in fact, ‘The World Clock’ website (linked above) uses TZ as a backend.

Ok, so we’ve got our database, what next? Well – looking down the list of libraries etc using TZ there aren’t any .NET based ones at all – nuts – this means we might have to create the API to the TZ database ourselves, or if we’re lucky – someone has already done this for us.

So a quick search for: ‘zoneinfo C#’ brings up a likely candidate – TZ4Net Library. Ahh HA! This is more like it – hopefully with this we can do the conversions we were after!

Time now for a quick program just to check this does indeed do what we’re after, and yes! It provides exactly what I wanted. The OlsonTimeZone class will use any ‘DateTime’ passed as an argument as a DateTime from the same zone.

Perhaps better explained: If you create two OlsonTimeZone instances:

And then convert an arbitrary DateTime (in this case 9am)

We get the output:

Converted: 09:00:00
EST: 14:00:00
PST: 17:00:00

So, zoneEST read the 09:00:00 as 9am EST time, zonePST as 9am PST. The reason this is important is because it makes no difference what the DateTime class thinks its own TimeZone is, whether it’s UTC or local, OlsonTimeZone will just ignore it.

The sample program below goes through a collection of values stored in an array printing out some information about the time zone selected – nothing special at all.

All that’s left is to say thanks to Zbigniew Babiej for writing the API!