Filter a String

Question

I want to make sure a string has only characters in this range

[a-z] && [A-Z] && [0-9] && [-]

so all letters and numbers plus the hyphen. I tried this...

C# App:

        char[] filteredChars = { ',', '!', '@', '#', '$', '%', '^', '&', '*', '(', ')', '_', '+', '=', '{', '}', '[', ']', ':', ';', '"', '\'', '?', '/', '.', '<', '>', '\\', '|' };
        string s = str.TrimStart(filteredChars);

This TrimStart() only seems to work with letters no otehr characters like $ % etc

Did I implement it wrong? Is there a better way to do it?

I just want to avoid looping through each string's index checking because there will be a lot of strings to do...

Thoughts?

Thanks!

Answer 1

This seems like a perfectly valid reason to use a regular expression.

bool stringIsValid = Regex.IsMatch(inputString, @"^[a-zA-Z0-9\-]*?$");

In response to miguel's comment, you could do this to remove all unwanted characters:

string cleanString = Regex.Replace(inputString, @"[^a-zA-Z0-9\-]", "");

Note that the caret (^) is now placed inside the character class, thus negating it (matching any non-allowed character).

Answer 2

Here's a fun way to do it with LINQ - no ugly loops, no complicated RegEx:

private string GetGoodString(string input)
{
   var allowedChars = 
      Enumerable.Range('0', 10).Concat(
      Enumerable.Range('A', 26)).Concat(
      Enumerable.Range('a', 26)).Concat(
      Enumerable.Range('-', 1));

   var goodChars = input.Where(c => allowedChars.Contains(c));
   return new string(goodChars.ToArray());
}

Feed it "Hello, world? 123!" and it will return "Helloworld123".

Answer 3

Why not just use replace instead? Trimstart will only remove the leading characters in your list...

Answer 4

Try the following

public bool isStringValid(string input) {
  if ( null == input ) { 
    throw new ArgumentNullException("input");
  }
  return System.Text.RegularExpressions.Regex.IsMatch(input, "^[A-Za-z0-9\-]*$");
}

Answer 5

I'm sure that with a bit more time you can come up wiht something better, but this will give you a good idea:

public string NumberOrLetterOnly(string s)
{
    string rtn = s;
    for (int i = 0; i < s.Length; i++)
    {
        if (!char.IsLetterOrDigit(rtn[i]) && rtn[i] != '-')
        {
            rtn = rtn.Replace(rtn[i].ToString(), " ");
        }
    }
    return rtn.Replace(" ", "");
}