Question

This is very weird. I have the following code:

Assert.AreEqual(new DateTime(2000, 1, 1), DateTime.ParseExact("2000", "yyyy", CultureInfo.InvariantCulture));
Assert.AreEqual(new DateTime(2000, 1, 1), DateTime.ParseExact("20000705", "yyyy", CultureInfo.InvariantCulture));

The first line passes, the second one fails with “System.FormatException: String was not recognized as a valid DateTime“.

I cannot shorten the string to be parsed to match the length of the format – it would work in this particular case, but this is part of a more generic method, and it would fail somewhere else. Any idea on why the second call fails?

[Edit] Ok, I was hoping it was parsing just as much of the input string as needed to satisfy the format.

I get a lot of strings in a lot of formats, and I have one method that accepts both and, after a bit of processing (I only get dates, so I replace “m” with “M” and “Y” with “y” and so on), I call DateTime.ParseExact. The reason I cannot call DateTime.Parse is because it doesn’t allow for a format argument… I can get ddMMyyyy in one part of the program and yyyyddMM in another, there’s no way for it to correctly figure it out.

[Edit 2] I guess it’s my fault… I’ll have to truncate the input when that issue arises. Fortunately I generally have all parts of the date in the format, this (just the year) is a rare occurence. Thanks for the help.

Answer 1

It failed because DateTime.ParseExact requires the input string to match the specified format exactly (err, I mean almost exactly, per your comment below), and “20000705” does not match “yyyy”.

To parse “20000705”, you’ll need to use a different technique – either ParseExact with an appropriate format string (like “yyyyMMdd”), or DateTime.Parse, which is a bit more forgiving (though also less accurate).

It looks like you’re trying to extract the year from the date string – no parse method will do that for you.

Instead you should get the actual DateTime represented by the string – July 5th 2000 or May 7th 2000, depending on your format – and then extract the year using DateTime.Year.