Re: [Boost-users] Boost.Regex: Iterate over named captures/groups

Subject: Re: [Boost-users] Boost.Regex: Iterate over named captures/groups
From: Anthony Foiani (tkil_at_[hidden])
Date: 2012-01-31 11:49:19

NoRulez <norulez_at_[hidden]> writes:

>    if I have a regex (e.g.: "^Subject: (Re: |Fw: )*(?<subject>.*)")
>
>    I know I can access them with what["subject"] but is there a way to get
>    a list or whatever of named captures/groups?

What would you expect to see?

You asked for a named group "subject", which matches zero or more
characters; as such, it will *always* match (if the whole match
succeeds) but it might be empty.

And as for "(Re: |Fw: )*", it will always be submatch 1, and its
contents will most likely be whatever it found on the last time
through.

You do have one good question here: I don't know how Boost.Regex would
signal that "(Re: |Fw: )*" didn't match at all.  (Perl would use undef
to distinguish between that case and the empty string, but C++ doesn't
have that option.)

And it looks like the answer is (surprise!) in the documentation
already:

   http://www.boost.org/doc/libs/1_48_0/libs/regex/doc/html/boost_regex/captures.html#boost_regex.captures.unmatched_sub_expressions
   (or: http://preview.tinyurl.com/846ls72 )

Hope this helps,
t.