C# Regexes: Named and numbered capturing groups

Question

Given

var re = new Regex(@"(?<name>\w+)(x)\1\2");
Console.WriteLine(re.IsMatch("yxxy"));

Prints True, it appears unnamed capturing groups are numbered starting with 1, and then named capturing groups are assigned numbers afterwords. Is this correct/intended behaviour?

Seems like a weird behaviour. Never tried what you've done above but I always thought it started from the left hand side with the numbering. — Tomas Jansson
– Tomas Jansson, Commented Nov 25, 2010 at 9:27
@mastoj: Yeah.... I thought it might too...which is why I had to investigate! — mpen
– mpen, Commented Nov 25, 2010 at 9:34

alpha-mouse · Accepted Answer · 2010-11-25 09:27:16Z

3

At least MSDN says so. http://msdn.microsoft.com/en-us/library/bs2twtah(VS.71).aspx. In the newer version of this article it is confirmed, but it's more difficult to find this info. Named matched subexpressions are numbered consecutively from left to right after matched subexpressions.

answered Nov 25, 2010 at 9:27

alpha-mouse

5,01328 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

tchrist Over a year ago

@Mark: You should be careful with this if moving to other programming languages’ regexes. It’s more common for the numbered groups to be strictly left-to-right, whether they also have a name or not.

Collectives™ on Stack Overflow

C# Regexes: Named and numbered capturing groups

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related