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;
    }

Answer 2

In order to check if the string is both a combination of letters and digits, you can re-write @jgauffin answer as follows using .NET 4.0 and LINQ:

if(!string.IsNullOrWhiteSpace(yourText) && 
yourText.Any(char.IsLetter) && yourText.Any(char.IsDigit))
{
   // do something here
}

Answer 3

I needed to check for A-Z, a-z, 0-9; without a regex (even though the OP asks for regex).

Blending various answers and comments here, and discussion from https://stackoverflow.com/a/9975693/292060, this tests for letter or digit, avoiding other language letters, and avoiding other numbers such as fraction characters.

if (!String.IsNullOrEmpty(testString)
    && testString.All(c => Char.IsLetterOrDigit(c) && (c < 128)))
{
    // Alphanumeric.
}

Answer 4

^\w+$ will allow a-zA-Z0-9_

Use ^[a-zA-Z0-9]+$ to disallow underscore.

Note that both of these require the string not to be empty. Using * instead of + allows empty strings.