Recursion in regular expression is not working

Question

I need to separate type and arguments in this expression:

tf->get_TextState()->set_TextMatrix(std::shared_ptr<DOM::Matrix>(new DOM::Matrix(m->get_M11(), -m->get_M12())));

I create the following regex:

std::shared_ptr[ \t]*<(?'type'[A-Z,:,_,a-z,<,>]*){1}>[ \t]*\([ \t]*new[ \t]*(\k'type'){1}(?'args'.*)

The result is:

Group "type": DOM::Matrix

Group "args": (m->get_M11(), -m->get_M12())));

The problem in a "args" group because I need only the: (m->get_M11(), -m->get_M12())

For do that, I change .* to: \([^()]*+(?:(?R)[^()]*+)*+\)

This expression separetly very well work on: (m->get_M11(), -m->get_M12()))); With expected result: (m->get_M11(), -m->get_M12())

But when I add it in whole pattern i.e.:

std::shared_ptr[ \t]*<(?'type'[A-Z,:,_,a-z,<,>]*){1}>[ \t]*\([ \t]*new[ \t]*(\k'type'){1}(?'args'\([^()]*+(?:(?R)[^()]*+)*+\))

It do not matching anything. What I'm doing wrong?

What is the output you're looking for (and what is the *+ supposed to do? — thebjorn
– thebjorn, Commented Mar 23, 2016 at 22:14

Wiktor Stribiżew · Accepted Answer · 2016-03-23 22:50:27Z

1

You just need to use a subroutine call to recurse the args subpattern with (?&args), but not the whole pattern ((?R) recurses the whole pattern!).

Use

std::shared_ptr\h*<(?'type'[A-Z:_a-z<>]*)>\h*\(\h*new\h*\k'type'(?'args'\([^()]*+(?:(?&args)[^()]*+)*+\))

See the regex demo

Note that I replaced [ \t] with \h (it matches horizontal whitespace) to shorten the pattern, removed redundant {1} quantifiers and groups.

BTW, here is an alternative expression that does the same thing:

std::shared_ptr\h*<(?'type'[A-Z:_a-z<>]*)>\h*\(\h*new\h*\k'type'(?'args'\((?>[^()]|(?&args))*\))

See another demo

answered Mar 23, 2016 at 22:50

Wiktor Stribiżew

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1 Comment

nen777w Over a year ago

Thank you Wiktor! Unfortunately I cant' set the +1 but in my case I estimate this answer +10

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