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

This class cleans filenames and paths; use it like

var myCleanPath = PathSanitizer.SanitizeFilename(myBadPath, ' ');

Here's the code;

/// 

/// Cleans paths of invalid characters.
/// 
public static class PathSanitizer
{
    /// 

    /// The set of invalid filename characters, kept sorted for fast binary search
    /// 
    private readonly static char[] invalidFilenameChars;
    /// 

    /// The set of invalid path characters, kept sorted for fast binary search
    /// 
    private readonly static char[] invalidPathChars;

    static PathSanitizer()
    {
        // set up the two arrays -- sorted once for speed.
        invalidFilenameChars = System.IO.Path.GetInvalidFileNameChars();
        invalidPathChars = System.IO.Path.GetInvalidPathChars();
        Array.Sort(invalidFilenameChars);
        Array.Sort(invalidPathChars);

    }

    /// 

    /// Cleans a filename of invalid characters
    /// 
    /// the string to clean
    /// the character which replaces bad characters
    /// 
    public static string SanitizeFilename(string input, char errorChar)
    {
        return Sanitize(input, invalidFilenameChars, errorChar);
    }

    /// 

    /// Cleans a path of invalid characters
    /// 
    /// the string to clean
    /// the character which replaces bad characters
    /// 
    public static string SanitizePath(string input, char errorChar)
    {
        return Sanitize(input, invalidPathChars, errorChar);
    }

    /// 

    /// Cleans a string of invalid characters.
    /// 
    /// 
    /// 
    /// 
    /// 
    private static string Sanitize(string input, char[] invalidChars, char errorChar)
    {
        // null always sanitizes to null
        if (input == null) { return null; }
        StringBuilder result = new StringBuilder();
        foreach (var characterToTest in input)
        {
            // we binary search for the character in the invalid set. This should be lightning fast.
            if (Array.BinarySearch(invalidChars, characterToTest) >= 0)
            {
                // we found the character in the array of 
                result.Append(errorChar);
            }
            else
            {
                // the character was not found in invalid, so it is valid.
                result.Append(characterToTest);
            }
        }

        // we're done.
        return result.ToString();
    }

}