Question

What is a good regular expression that can validate a text string to make sure it is a valid Windows filename? (AKA not have \/:*?'<>| characters).

I’d like to use it like the following:

// Return true if string is invalid. if (Regex.IsMatch(szFileName, '<your regex string>')) {     // Tell user to reformat their filename. } 

Answer 1

As answered already, GetInvalidFileNameChars should do it for you, and you don’t even need the overhead of regular expressions:

if (proposedFilename.IndexOfAny(System.IO.Path.GetInvalidFileNameChars()) != -1) {   MessageBox.Show('The filename is invalid');   return; }