C＃DateTime.TryParse格式相同，日期不同

Question

DateTime res;
String s;

s = "Wed, 28 Mar 2012 10:30:52 GMT";
DateTime.TryParse(s, out res);
Console.WriteLine(s + " => " + res);

s = "Fri, 15 May 2009 20:10:57 GMT";
DateTime.TryParse(s, out res);
Console.WriteLine(s + " => " + res);

Output:

Wed, 28 Mar 2012 10:30:52 GMT => 01/01/0001 00.00.00
Fri, 15 May 2009 20:10:57 GMT => 15/05/2009 22.10.57

Why does it work only for some dates? Obviously I ran that code on the same machine at the same time.

Answer 1

I expect that the long-date format of the culture you're working in probably only accepts the full month name as suggested by @VimalStan (have you confirmed this either way, yet?).

It should (IMHO) accept what you're trying to doing too, but I'm aware that various cultures can have "quirks" like this. eg perhaps "mar" is ambiguous in some cultures? (and while it may not be ambiguous in your culture... perhaps some code has hung-over from one culture to another... I don't know how culture rules are even implemented, so don't really know if this is even a valid suggestion... but my point that a particular culture may not always behave as expected, I think, is fair).

Use http://msdn.microsoft.com/en-us/library/system.globalization.cultureinfo.currentculture.aspx to check which culture your .NET context is running in. You can view what context your windows user profile is running in via the control panel (eg "Region and Language" on Win 7), and take a peek at the long date format there.

Your example works fine on my pc, where the long date format is "dddd, d MMMM yyyy". I'm in Australia, using en-au.

As a test, try using en-au "English (Australia) as your culture (via control panel, or explicitly set as per the above currentculture link, at the "Explicitly Setting the CurrentCulture Property" heading, and then test if your code works as expected.

If it works as expected, I think that means the problem is just that your culture is a little more strict in its parsing, than eg mine is (and eg than what you expected). And hence, you may need to ensure you pass the full month, or specify your own specific parsing pattern as per another answer here using TryParseExact() .

Answer 2

I had the same sort of issue the other day, it was very frustrating as there was no need for it to fail.

However the way i fixed the issue was to move to DateTime.TryParseExact

which is used like:

// Parse date with no style flags.
dateString = " 5/01/2009 8:30 AM";
if (DateTime.TryParseExact(dateString, "g", enUS, 
                          DateTimeStyles.None, out dateValue))
   Console.WriteLine("Converted '{0}' to {1} ({2}).", 
                             dateString, 
                              dateValue, 
                             dateValue.Kind);
else
   Console.WriteLine("'{0}' is not in an acceptable format.", dateString);

Since switching parsing has never failed

Answer 3

Try this:

DateTime res;
String s = "Wed, 28 Mar 2012 10:30:52 GMT";
DateTime.TryParseExact(s, "R", CultureInfo.InvariantCulture, DateTimeStyles.None, out res);

This will give: {3/28/2012 10:30:52 AM}

Also, when

String s = "Fri, 15 May 2009 20:10:57 GMT";

This will give: {5/15/2009 8:10:57 PM}

Answer 4

It's only a guess, but perhaps the matter is that in italian "Mar" is the beginning of the word "Martedì" (Tuesday), so "Wed, 28 Mar 2012 10:30:52 GMT" could be misinterpreted as something like "Wednesday Martedì/Tuesday" which is absurd.

As a counterexample, I looked for a Martedì/Tuesday 28 in 2013 and it works substituting the day of week with the month:

May, 28 Mar 2013 10:30:52 GMT => 28/05/2013 12.30.52

Obviously it couldn't work using other locales.