Can I test if a regex is valid in C# without throwing exception

Question

I allow users to enter a regular expression to match IP addresses, for doing an IP filtration in a related system. I would like to validate if the entered regular expression

Answer 1

I think exceptions are OK in this case.

Just make sure to shortcircuit and eliminate the exceptions you can:

private static bool IsValidRegex(string pattern)
{
    if (string.IsNullOrWhiteSpace(pattern)) return false;

    try
    {
        Regex.Match("", pattern);
    }
    catch (ArgumentException)
    {
        return false;
    }

    return true;
}

Answer 2

I've ever been use below function and have no problem with that. It uses exception and timeout both, but it's functional. Of course it works on .Net Framework >= 4.5.

    public static bool IsValidRegexPattern(string pattern, string testText = "", int maxSecondTimeOut = 20)
    {
        if (string.IsNullOrEmpty(pattern)) return false;
        Regex re = new Regex(pattern, RegexOptions.None, new TimeSpan(0, 0, maxSecondTimeOut));
        try { re.IsMatch(testText); }
        catch{ return false; } //ArgumentException or RegexMatchTimeoutException
        return true;
    }