嵌套量词* C＃正则表达式与美国电话号码匹配的例外

Question

The following expression is supposed to match US phone numbers:

\(?\d{3}\)?-? *\d{3}-? *-?\d{4}

However, when I use it in my program it thows an error:

parsing "(?\\d{3})?-? *\\d{3}-? *-?\\d{4}" - Nested quantifier *.

I just can't see where the error is. :(

It works well with regex101 for:

(111) 111-1111
111-111-1111
1111111111

but does not seem to work when used with C# Regex.

I appreciate any guidance. TIA

(C# VS2010 .NET 4.0)

Edit: This fixes the problem:

 \(?\d{3}\)?-?\s*\d{3}-?\s*-?\d{4}

Still don't know why there was a Nested quantifier error though?

Answer 1

The problem with your first regex is that it contains literal spaces that are ignored when using RegexOptions.IgnorePatternWhitespace option. See this demo , check the Ignore Whitespace option to reproduce the issue.

Your first regex is thus equal to

\(?\d{3}\)?-?*\d{3}-?*-?\d{4}
             ^       ^

To make this regex work, do not use the RegexOptions.IgnorePatternWhitespace option, or the * quantifier will be applied to the ? quantifier which is not allowed in .NET regex.

Or replace the spaces with [ ] , or \\s . Eg

\(?\d{3}\)?-?[ ]*\d{3}-?[ ]*-?\d{4}

The space inside a character class is not ignored when using RegexOptions.IgnorePatternWhitespace flag (see RegexOptions Enumeration MSDN page ).

See demo

Answer 2

Maybe this?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;


namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Regex RegexObj = new Regex("\\(?\\d{3}-?\\)?\\s*\\d{3}-?\\s*-?\\d{4}");
            String Str1 = "(111) 111-1111";
            String Str2 = "111-111-1111";
            String Str3 = "1111111111";
            Console.Write(RegexObj.IsMatch(Str1).ToString() + '\n');
            Console.Write(RegexObj.IsMatch(Str2).ToString() + '\n');
            Console.Write(RegexObj.IsMatch(Str3).ToString() + '\n');


            Console.Read();
        }
    }
}