In Boost library, there are totally three libraries to support regex parser, regex, xpressive and ..
the xpressive library is static compile, that means it will cause a lot of time to build your project even if you just change small piece of code.
Regex usage
if (what.size() - 1 > 0)
urls.push_back(what[1].str());
});
urls.push_back(what[1].str());
});
the first match group is start index is 1. 0 is for the whole match for the regex syntax.