How do I check if a given string is a legal/valid file name under Windows?

Question

I want to include a batch file rename functionality in my application. A user can type a destination filename pattern and (after replacing some wildcards in the pattern) I n

Answer 1

Regular expressions are overkill for this situation. You can use the String.IndexOfAny() method in combination with Path.GetInvalidPathChars() and Path.GetInvalidFileNameChars().

Also note that both Path.GetInvalidXXX() methods clone an internal array and return the clone. So if you're going to be doing this a lot (thousands and thousands of times) you can cache a copy of the invalid chars array for reuse.