Fastest way to format a phone number in C#?

Question

What is the fastest way to format a string using the US phone format [(XXX) XXX-XXXX] using c#?

My source format is a string.

Answer 1

Not the fastest way, but you can use Extension Methods (note that the parameter must be cleaned up of any previous phone format):

public static class StringFormatToWhatever
{
    public static string ToPhoneFormat(this string text)
    {        
        string rt = "";
        if (text.Length > 0)
        {            
            rt += '(';
            int n = 1;
            foreach (char c in text)
            {
                rt += c;
                if (n == 3) { rt += ") "; }
                else if (n == 6) { rt += "-"; }
                n++;
            }
        }
        return rt;
    }
}

Then, use it as

myString.ToPhoneFormat();

Modify to your needs if you want to:

• Include phone extension (x1234)
• Clean the parameter of any existing phone format inside the method
• Use dash instead of parenthesis
• Eat a sandwich ... you name it! :)

You can also use this to format the string in each user input.