Problem with subexpresions

From: Chris (chris_at_[hidden])
Date: 2001-04-29 21:25:29

Hiya,

I've been messing with boost's regex class, but I can't figure out
sub-expressions for the life of me. I understand that I call
regex_match(), and pass it a match_results, but I just don't
understand match_results - particularly struct sub_match .

For example, look at this little piece of code . . .

#include <iostream>
#include <boost\regex.hpp>

using namespace boost;
using namespace std;

int main(int argc, char* argv[])
{
        regex rxHeader("(\\w+), (\\w+)");
        cmatch matches;

        if (regex_match("Moose, Orangutang", matches, rxHeader))
        {
                cout << matches[1].first << endl;
        }
        else
                puts("No match.");

        return 0;
}

I expect matches[1].first to return "Moose", the first match. But it
doesn't - it returns "Moose, Orangutang". matches[2].first returns
"Orangutang", which makes some sense.

Actually, I don't understand this whole first/second business in
sub_matches. In any other language, matches[0] would just be a string
or something. But here, obviously things are being done differently,
and just don't understand what the scheme is here. I've read the docs
over and over, and I can't find a darn thing.

Any help?

Thanks,
Chris