gistfile1.cpp

std::map<std::string, std::string> result;

std::string str("foo=bar&color=red&zoom=22.5&alpha=3,4,2,1222.8");
 
sregex pair = ( (s1= +_w) >> "=" >> (s2= +(set[alnum | '_' | '.' | ',']) ))
[ ref(result)[s1] = s2];

sregex rx = pair >> *('&' >> *(pair)); 

if(regex_match(str, rx)) {
	std::map<std::string, std::string>::const_iterator it;

	for (it = result.begin(); it != result.end(); ++it) {
		std::cout << "key '" << it->first << "' value '" << it->second << "'" << std::endl;
	}
}