Boost logo

Boost :

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.


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

Boost list run by bdawes at, gregod at, cpdaniel at, john at