How can I validate a string to only allow alphanumeric characters in it?

Question

How can I validate a string using Regular Expressions to only allow alphanumeric characters in it?

(I don\'t want to allow for any spaces either).

Answer 1

Same answer as here.

If you want a non-regex ASCII A-z 0-9 check, you cannot use char.IsLetterOrDigit() as that includes other Unicode characters.

What you can do is check the character code ranges.

• 48 -> 57 are numerics
• 65 -> 90 are capital letters
• 97 -> 122 are lower case letters

The following is a bit more verbose, but it's for ease of understanding rather than for code golf.

    public static bool IsAsciiAlphaNumeric(this string str)
    {
        if (string.IsNullOrEmpty(str))
        {
            return false;
        }

        for (int i = 0; i < str.Length; i++)
        {
            if (str[i] < 48) // Numeric are 48 -> 57
            {
                return false;
            }

            if (str[i] > 57 && str[i] < 65) // Capitals are 65 -> 90
            {
                return false;
            }

            if (str[i] > 90 && str[i] < 97) // Lowers are 97 -> 122
            {
                return false;
            }

            if (str[i] > 122)
            {
                return false;
            }
        }

        return true;
    }