How to remove illegal characters from path and filenames?

Question

I need a robust and simple way to remove illegal path and file characters from a simple string. I\'ve used the below code but it doesn\'t seem to do anything, what am I miss

Answer 1

The best way to remove illegal character from user input is to replace illegal character using Regex class, create method in code behind or also it validate at client side using RegularExpression control.

public string RemoveSpecialCharacters(string str)
{
    return Regex.Replace(str, "[^a-zA-Z0-9_]+", "_", RegexOptions.Compiled);
}

OR