CODEWITHSUNDEEP
vb.nettimezone
user1447679
user1447679

Reputation: 3240

Is there a more elegant way to convert this time to my server's local time?

I have a string in the following format:

14:41:21 Dec 15, 2015 PST

I want to convert that to my server's local time, but I think I'm creating an extra step that can be avoided:

Dim testdate As Date
DateTime.TryParseExact(dateinput, "HH:mm:ss MMM dd, yyyy PST", CultureInfo.InvariantCulture, DateTimeStyles.None, testdate)
testdate = TimeZoneInfo.ConvertTimeToUtc(testdate, TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time"))
testdate = testdate.ToLocalTime()

I've played around with this but always off by a couple hours either way, and the above is what I've found to work but just wanted to know if there was a better way. Also note it could be deployed on multiple servers, so I don't want to specify the timezone to convert it to explicitly, reason for localtime.

Upvotes: 0

Views: 45

Answers (1)

Matt Johnson-Pint
Matt Johnson-Pint

Reputation: 241535

A few things:

  • If you're going to include fixed text in a format string, put it in single-tick quotes so it can't get misinterpreted as a formatting token. ('PST')

  • In the general case, time zone abbreviations should only be used for display purposes. They should not be parsed as input, as they could be ambiguous. For example, there are 5 different interpretations of CST. It might be US Central Standard Time, but it could also be China Standard Time, or one of the others. See the list on Wikipedia.

  • If you have a limited number of time zone abbreviations you want to support, then you could extract it from the string and use a dictionary, select/case statements, or conditional logic to map them. Just be certain you know the entire set of abbreviations you want to support and exactly which time zones you want them to map to. Also be sure to account for daylight time abbreviations, such as PDT.

  • Note that some older standards, such as RFC 2822 §4.3 indeed hardcode a few abbreviations, so you may choose to support those if you are parsing that particular format. (Yours is similar, but not quite a match.)

  • Your code is mostly ok, but you should probably check the result of TryParseExact. Otherwise you might as well use ParseExact which will throw an exception on failure instead of just returning false.

  • You could use ConvertTime with TimeZoneInfo.Local as the destination zone if you wanted to do the conversion in a single step. The code would be slightly smaller, though would have no technical differences.

  • Are you sure you really want to do this? Relying on the system's local time zone should usually should not be done in server-based applications. That's something more appropriate for desktop and mobile. In general, server-side code should not rely on the system time zone to be anything in particular. Avoid "local time" APIs, including DateTime.Now, TimeZoneInfo.Local, ToLocalTime, and ToUniversalTime (when it assumes the input is local time). It is better to supply the applicable time zone in your business logic or application configuration.

Upvotes: 1

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