Use of undeclared identifier 'client' netlib 0.13.0

When I try the above code, I get "use of undeclared identifier 'client' " on line 8:

#include <boost/network/protocol/http/client.hpp>
#include <boost/network.hpp>

using namespace boost::network;
using namespace boost::network::http;

int main():
    {client::request request_("https://www.youtube.com/results?search_query=a");
    request_ << header("Connection", "close");
    client client_;
    client::response response_ = client_.get(request_);
    std::string body_ = body(response_);
}

I want to get the title of the first YouTube video search result and I'm trying to do like this. Thanks for your help!