boost-asio如何知道运行服务器的端口？

Question

所以我正在浏览asio教程,并编译了同步的日间客户端和同步的日间服务器.我正在玩服务器端的代码,通过命令行传入端口(在网站的代码中,他们硬编码13作为端口).

我注意到,如果服务器在端口13上运行,客户端只能连接,但有趣的是客户端上没有说服务器所在的端口.

任何人都可以向我解释这个程序如何知道服务器运行的端口以及为什么它只适用于端口13？这是服务器的代码http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio/tutorial/tutdaytime2/src.html

//
// client.cpp
// ~~~~~~~~~~
//
// Copyright (c) 2003-2010 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::resolver::iterator end;

    tcp::socket socket(io_service);
    boost::system::error_code error = boost::asio::error::host_not_found;
    while (error && endpoint_iterator != end)
    {
      socket.close();
      socket.connect(*endpoint_iterator++, error);
    }
    if (error)
      throw boost::system::system_error(error);

    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;
}

Answer 1

有趣的是,客户端没有说服务器端口是什么

客户端中的服务器端口是硬编码的:

tcp::resolver::query query(argv[1], "daytime");

关键是"白天".它是标准协议,标准端口号为13