is there a way make a character to be part of two matches not only one

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I have this regex: 1(0+)1

and I'm testing against this value: 1010010001,

I'm expecting that I have three matches: 101, 1001, 10001 but the matches that I got are only: 101, 10001.

the second 1 should be part of the two matches: 101 and 1001.

is there a way make a character to be part of two matches ?

https://regex101.com/r/oNfdFU/1

regex c#
2 Answers

Here is a way to do this in C#. We can find all matches on the regex pattern 10+(?=1). This uses a lookahead at the end of the pattern to assert a trailing 1, but note that the trailing 1 does not actually get consumed in each match. It gets consumed in the start of the following match. Then, to build the actual output match, we need to append a 1 to the end of each match.

string input = "1010010001";
Regex regex = new Regex(@"10+(?=1)");
MatchCollection matches = regex.Matches(input);
foreach(Match match in matches)
{
    Console.WriteLine("Found a match: {0}1", match.Value);
}

This prints:

Found a match: 101
Found a match: 1001
Found a match: 10001
user_18632290

You can use a capturing lookahead to capture overlapping matching groups.

In this case:

(?=(10+1))
^ ^      ^     look ahead
    ^  ^       fixed '1' The second can overlap (the first never will on LH)
     ^         '0' one or more times also can overlap
    ^   ^      capture what is seen in the look ahead

Demo

The lookahead is looking ahead and capturing in one step. It then increments by one character and tries again -- so moving through the string by each left hand 1.

Same regex works in C#

Demo

Or, in C#:

string input = "1010010001";
Regex regex = new Regex(@"(?=(10+1))");
MatchCollection matches = regex.Matches(input);
foreach(Match match in matches)
    {
        Console.WriteLine("Found a match: {0}", match.Groups[1]);
    }

Prints:

Found a match: 101
Found a match: 1001
Found a match: 10001

BTW: .NET allows variable width lookBEHINDS so you can also do:

(?<=(10+1))

But that is fairly unique to .NET. PCRE and most other regex flavors require fixed length strings for look behinds...

Demo

user_2986070
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