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

From: Eric Niebler (eric_at_[hidden])
Date: 2006-01-03 04:43:57

Eric Niebler wrote:
> 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.

<snip>

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

Fixed. Please get the latest version of xpressive from the Vault. Below 
is a nice little program that will parse your messages and print out the 
name/value pairs. It also is a nice little demo of backrefs and nested 
results. I may use this in xpressive's docs, with your permission. I'll 
definitely add this as a test case.

#include <string>
#include <iostream>
#include <boost/foreach.hpp>
#include <boost/xpressive/xpressive.hpp>
using namespace std;
using namespace boost::xpressive;

int main()
{
     std::string buffer =
         "FROGGIE\r\n"
         "Volume = 1\r\n"
         "Other1= 2\r\n"
         "Channel=3\r\n"
         "Other =4\r\n"
         "\r\n"
         "FROGGIE\r\n"
         "Volume = 5\r\n"
         "Other1= 6\r\n"
         "Channel=7\r\n"
         "Other =8\r\n"
         "\r\n"
         "FROGGIE\r\n"
         "Volume = 9\r\n"
         "Other1= 0\r\n"
         "Channel=10\r\n"
         "\r\n";

     mark_tag name(1), value(2);

     sregex name_value_pair_ =
       (name= +alnum) >> *_s >> "=" >> *_s >>
       (value= +_d) >> *_s >> _ln;

     sregex message_ =
       *_s >> "FROGGIE" >> _ln >> +name_value_pair_ >> _ln;

     sregex re_ = +message_;
     smatch what;

     if(regex_search(buffer, what, re_))
     {
         cout << "Msg count: " << what.nested_results().size() << endl;
         BOOST_FOREACH(smatch const &msg, what.nested_results())
         {
             cout << "Message:\n" << msg[0] << endl;
             cout << "  name/value pair count: "
                  << msg.nested_results().size() << endl;
             BOOST_FOREACH(smatch const &nvp, msg.nested_results())
             {
                 cout << "  name:" << nvp[name]
                      << ", value:" << nvp[value] << endl;
             }
         }
     }

     return 0;
}

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