Question

Based on this answer…
Using a regular expression to validate an email address

Which led me to this site…
http://fightingforalostcause.net/misc/2006/compare-email-regex.php

I’d like to use this regex for email validation for my ASP.NET MVC app:

/^[-_a-z0-9\'+*$^&%=~!?{}]++(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*+@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d++)?$/iD

Unfortunately, I get this error

System.ArgumentException was unhandled by user code
Message=”parsing \”/^[-_a-z0-9\’+$^&%=~!?{}]++(?:\.[-_a-z0-9\’+$^&%=~!?{}]+)*+@(?:(?![-.])[-a-z0-9.]+(?

Has anyone ever converted this to be usable by .NET’s Regex class, or is there another .NET regular expression class that is a better fit with PHP’s preg_match function?

Answer 1

The problem with your regular expression in .NET is that the possessive quantifiers aren’t supported. If you remove those, it works. Here’s the regular expression as a C# string:

@"^[-_a-z0-9\'+*$^&%=~!?{}]+(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d+)?$"

Here’s a test bed for it based on the page you linked to, including all the strings that should match and the first three of those that shouldn’t:

using System;
using System.Text.RegularExpressions;

public class Program
{
    static void Main(string[] args)
    {
        foreach (string email in new string[]{
            "[e-mail]",
            "[e-mail]",
            "hasApostrophe.o'[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "IPInsteadOfDomain@127.0.0.1",
            "IPAndPort@127.0.0.1:25",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "[e-mail]",
            "&*=?^+{}'~@validCharsInLocal.net",
            "missingDomain@.com",
            "@missingLocal.org",
            "missingatSign.net"
        })
        {
            string s = @"^[-_a-z0-9\'+*$^&%=~!?{}]+(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d+)?$";
            bool isMatch = Regex.IsMatch(email, s, RegexOptions.IgnoreCase);
            Console.WriteLine(isMatch);
        }
    }
}

Output:

True
True
True
True
True
True
True
True
True
True
True
True
True
True
True
True
True
True
False
False
False

A problem though is that it fails to match some valid email-addresses, such as foo\@[e-mail]. It’s better too match too much than too little.