How does boost::asio figure out what port to connect to?

So I decided to take a step forward after my C++ course, by learning how to do some networking. After following the example of how to use boost::asio to make a synchronous client, everything went well, but I was stumped when trying to figure out what part of the program actually deals with the port. I understand you enter an IP address (eg. I used 127.0.0.1 as the argument for the program. I ran the code via command line: `# client 127.0.0.1` Also, the server side of the code, runs on port 13, shown here: http://www.boost.org/doc/libs/1_52_0/doc/html/boost_asio/tutorial/tutdaytime2.html Here is the full code from the website: (also can be found here: http://www.boost.org/doc/libs/1_52_0/doc/html/boost_asio/tutorial/tutdaytime1.html ``` // // client.cpp // ~~~~~~~~~~ // // Copyright (c) 2003-2012 Christopher M. Kohlhoff (chris at kohlhoff dot com) // // Distributed under the Boost Software License, Version 1.0. (See accompanying // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) // #include <iostream> #include <boost/array.hpp> #include <boost/asio.hpp> using boost::asio::ip::tcp; int main(int argc, char* argv[]) { try { if (argc != 2) { std::cerr << "Usage: client <host>" << std::endl; return 1; } boost::asio::io_service io_service; tcp::resolver resolver(io_service); tcp::resolver::query query(argv[1], "daytime"); tcp::resolver::iterator endpoint_iterator = resolver.resolve(query); tcp::socket socket(io_service); boost::asio::connect(socket, endpoint_iterator); for (;;) { boost::array<char, 128> buf; boost::system::error_code error; size_t len = socket.read_some(boost::asio::buffer(buf), error); if (error == boost::asio::error::eof) break; // Connection closed cleanly by peer. else if (error) throw boost::system::system_error(error); // Some other error. std::cout.write(buf.data(), len); } } catch (std::exception& e) { std::cerr << e.what() << std::endl; } return 0; } ```