c++ - boost-asio 如何知道服务器正在运行的端口？

Question

所以我浏览了 asio 教程并编译了同步白天客户端和同步白天服务器。我通过更改要通过命令行传入的端口(在站点代码中将 13 硬编码为端口)来玩弄服务器端的代码。

我注意到客户端只有在服务器运行在端口 13 上时才能连接，但有趣的是，客户端上没有任何内容说明服务器在哪个端口上。

任何人都可以向我解释这个程序如何知道服务器在哪个端口上运行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

interestingly enough nothing on the client said what port the server was on

客户端的服务器端口在这里硬编码:

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

关键是“白天”。这是a standard protocol并且有它的标准端口号 13