Replacing strings using regex in .NET

Question

I'm building a generic regular expression validator which takes in a value to compare and returns true or false on whether it is a match or not. The validator is tied to custom controls and hence the input is automatically retrieved from a property. I would like to know if .NET has syntax for string replacement within the regex. I don't mean using the Regex.Replace method, I mean using the actual regular expression as a mechanism to replace text with something else. That way I can do:

return Regex.IsMatch(control.Text, "some regex with replacement logic built in");

More specifically I would like my regex to remove all non numeric values and then make sure it's within a number of characters.

Are you replacing the non-numeric values with something or just removing them? — Jetti
– Jetti, Commented Mar 14, 2012 at 15:14
Sounds like you want a one-liner, but the problem is such that you need two lines. This doesn't seem like it would be too bad if you could first use a regex.replace to remove non-numeric characters, then run a match on an 'all numeric characters?' expression. You could probably switch your UI to use a masked text box and save a lot of trouble, though. — djdanlib
– djdanlib, Commented Mar 14, 2012 at 15:16
Just make it 2 steps. First clean up control.Text, then match it. — Henk Holterman
– Henk Holterman, Commented Mar 14, 2012 at 15:16

MoonKnight · Accepted Answer · 2012-03-14 15:21:46Z

The 'MatchEvaluator Delegate' might help you here, although it is not explicitly what you requested; take a look...

Regex.Replace has an overload that takes a MatchEvaluator delegate, which is invoked per match. This allows you to delegate the content of the replacement string in C# code when the regular expression syntax is not expressive enough. For example:

Console.WriteLine(Regex.Replace("5 is less than 10", @"\d+", 
    m => (int.Parse(m.Value) * 10).ToString()));

give the output "5 is less than 100". This might be suitable here, but requires you to provide a generic replacement type.

I hope this helps.

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