Regex matches missing one match?

Question

I have the regex 1(0*)1 and the test string 1000010001

I want to have 2 matches, but I find that only 1 gets found :

var re         


        

Answer 1

You need to match overlapping strings.

It means you should wrap your pattern with a capturing group (( + your pattern + )) and put this consuming pattern into a positive lookahead, then match all occurrences and grab Group 1 value:

(?=(YOUR_REGEX_HERE))

Use

var regex = new Regex("(?=(10*1))");
var values = regex.Matches(intBinaryString)
    .Cast()
    .Select(m => m.Groups[1].Value)
    .ToList();

See the regex demo