[Boost-users] boost regex and match_partial

From: Angus Leeming (angus.leeming_at_[hidden])
Date: 2003-09-26 09:49:16

I'm afraid I haven't got the hang of match_partial.

Below is a little code with two functions that I think should produce 
identical results, but don't.

In strip_commas_try1 I use:
        boost::regex const front("^( *[[],*)(.*)$");
        regex_match(it, end, what, front);
In strip_commas_try2 I use:
        boost::regex const front("^( *[[],*)");
        regex_match(it, end, what, front, boost::match_partial);

Why does this second case not result in
        what[0].matched
?

Many thanks,
Angus

(This is with BOOST_VERSION 103002 and 
g++ (GCC) 3.2 20020903 (Red Hat Linux 8.0 3.2-7)).

#include<iostream>
#include<string>
#include <boost/regex.hpp>

using std::string;

string const strip_commas_try1(string const & input)
{
        string::const_iterator it  = input.begin();
        string::const_iterator end = input.end();

        // Strip any commas that follow immediately after the '['.
        // "[,,,,foo..." -> "foo..."
        boost::regex const front("^( *[[],*)(.*)$");

        boost::smatch what;
        regex_match(it, end, what, front);
        if (!what[0].matched) {
                std::cout << "Try 1 failed" << std::endl;
                return string();
        }
        it =  what[1].second;
        string const result = string(it, end);
        std::cout << "Try 1: " << result << std::endl;
        return result;
}

        
string const strip_commas_try2(string const & input)
{
        string::const_iterator it  = input.begin();
        string::const_iterator end = input.end();

        // Strip any commas that follow immediately after the '['.
        // "[,,,,foo..." -> "foo..."
        boost::regex const front("^( *[[],*)");

        boost::smatch what;
        regex_match(it, end, what, front, boost::match_partial);
        if (!what[0].matched) {
                std::cout << "Try 2 failed" << '\n';
                return string();
        }
        it =  what[1].second;
        string const result = string(it, end);
        std::cout << "Try 1: " << result << std::endl;
        return result;
}

        
int main()
{
        string const input = "[,,,foo,,,,bar,,,gaz,,]";
        std::cout << "Input: " << input << std::endl;

        strip_commas_try1(input);
        strip_commas_try2(input);

        return 0;
}