Re: [boost] [xpressive] Problem accessing repeating embedded pattern.

From: Eric Niebler (eric_at_[hidden])
Date: 2006-01-02 21:24:20

Dick Bridges wrote:
> I am trying to use Xpressive for parsing string-based message buffers. 

<snip>

You are confusing a backreference with a nested regex. A backreference 
(s1, s2, etc.) is accessed positionally from the match results struct 
like what[1], what[2], etc.

In contrast, when you nest a regex in another regex, you ended up with 
nested match results. You can access them with what.nested_results(), 
which is a collection of nested results, each result corresponding to an 
invocation of a nested regex (and each of which may contain other nested 
results, ad infinitum).

In your example ...

     sregex message_ =
       (*_s >> "FROGGIE" >> _ln >>
          +(+alnum >> *_s >> "=" >> *_s >> +_d >> *_s >> _ln)
       >> _ln);

     sregex re_ = +message_;
     smatch what;

     if( regex_search( buffer, what, re_ ) )
     {
         cout << "Count: " << what.nested_results().size() << endl;
         BOOST_FOREACH(smatch const &msg, what.nested_results())
         {
             cout << "Message:\n" << msg[0] << endl;
         }
     }

This displays the three messages one at a time (as long as you add one 
extra newline at the end of the last messge, otherwise your regex only 
matches the first two messages).

You'll notice that I eliminated your name_value_pair_ regex. That's 
because it exposed a bug in xpressive. :-P

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com