What is the “correct” way to replace from a list chars in a string?

Question

Often I need to clean a file name using Path.GetInvalidFileNameChars(), however I do not know of a way to search for any of the invalid letters (except by using Regex) in one pass.

public string LoopMethod()
{
    StringBuilder sb = new StringBuilder(fileName);
    foreach(var invalidChar in Path.GetInvalidFileNameChars())
    {
        sb.Replace(invalidChar, '_');
    }
    return sb.ToString();
}


Regex invalidCharsRegex;
public void RegexMethodInit()
{
    var invalidChars = Path.GetInvalidPathChars().Select(c => Regex.Escape(c.ToString())).ToString();
    invalidCharsRegex = new Regex(string.Join("|", invalidChars));
}

public string RegexMethod(string fileName)
{
    return invalidCharsRegex.Replace(fileName, "_");
}

Is one of those ways the "correct" way to to this or is there a better function I am missing?

Answer 1

foreach(var c in Path.GetInvalidPathChars())
    path = path.replace(c, '_')

That's a bit inefficient as it can allocate a string on every itteration, but usually not a problem. Alternative:

var chars = Path.GetInvalidPathChars()
path = new string(path.Select(c => chars.Contains(c) ? '_' : c).ToArray())

Answer 2

This should be fairly fast (though I did not try to compile or run). The number of lines can probably be greatly reduced with LINQ.

public static IEnumerable<char> EnumerateFileNameAsChars(string fileName, char replaceChar = '_')
{
    var invalidChars = new HashSet<char>(Path.GetInvalidFileNameChars());
    foreach (char c in fileName)
    {
        if (invalidChars.Contains(c))
        {
            yield return replaceChar;
        }
        else
        {
            yield return c;
        }
    }
}

// And finally ...
public static string CleanUpFileName(string fileName, char replaceChar = '_')
{
    return String.Concat(EnumerateFileNameAsChars(fileName, replaceChar));
}