Extract link from HTML using RE2

extract_link.cpp

RE2 link("(?ims)(?:\\<a([^\\>]+)href=\\\")([^\\\"]+)\\\"");
re2::StringPiece content(html_text);
string match;
string domain;
while(RE2::FindAndConsume(&content, link, (void*)0, &match)){
        if(match[0] == '/'){
                if(!domain.size()){
                        evbuffer_add_printf(evb, "Domain name required.\n");
                        evhttp_send_reply(req, HTTP_BADREQUEST, "Client", evb);
                        break;
                }
                match = domain + match;
                fprintf(stderr, "%s\n", match.c_str());
        }else{
                fprintf(stderr, "%s\n", match.c_str());
        }
}