.NET Regex Error: [x-y] range in reverse order

Question

I am creating a Regex and so far I did this and tried it,

 ^([0][1-9]|1[0-2])[/-.]

and I get the following error.

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Answer 1

The problem is with this part:

[/-.]

That means "the range of characters from '/' to '.'" - but '/' comes after '.' in Unicode, so the range makes no sense.

If you wanted it to mean "slash, dash or period" then you want:

[/\-.]

... in other words, you need to escape the dash. Note that if this is in a regular C# string literal, you'll need to perform another level of escaping too:

string pattern = "[/\\-.]";

Using a verbatim string literal means you don't need to escape the backslash:

string pattern = @"[/\-.]";

Alternatively, as Jay suggested, you can just put the dash at the start:

[-/.]

or end:

[/.-]

(I've just tested, and all three of these options work.)