insert hyphen in a 9 digit number after 5 digits using regex

Question

I have to automatically insert a hyphen in 9 digit number on text change event in c# only not javascript.

So if my number is 123456789 then it automatically becomes 12345-6789.

I would like to use regex.match.

My try:

The regex "^\\d{5}(-\\d{4})?$" is how the result should be.

so,

Regex regTest = new Regex("^\\d{5}(-\\d{4})?$");

Match match = regTest.Match(s);

if (match.Success)
           {
              var numString = match.Value;
           }

But the above does not returns a success.

Thanks for help.

Answer 1

Your code sample simply checks that the format is xxxxx-xxxx . It doesn't insert the hyphen.

You do not need a RexEx to insert a hyphen:

myString.Insert(5, "-");

Answer 2

The regular expression seems correct. You can verify it here:
http://derekslager.com/blog/posts/2007/09/a-better-dotnet-regular-expression-tester.ashx

Most probably you are not inserting the '-' and then matching.