C++ boost/asio 客户端不连接到服务器

Question

我正在学习 boost/asio ad write 2 programs (client and server) from e-book with small changes。 基本上它应该连接到我的服务器。 当我尝试连接到外部世界(一些随机的 http 服务器)时，一切都很好并且可以正常工作，但是当我将目标更改为“localhost:40002”时，它说参数无效。

客户端代码:

#include <boost/asio.hpp>
#include <iostream>

int main () {
   try {
      boost::asio::io_service io_service;
      boost::asio::ip::tcp::resolver::query query("localhost", 40002);
      boost::asio::ip::tcp::resolver resolver(io_service);
      boost::asio::ip::tcp::resolver::iterator destination = resolver.resolve(query);
      boost::asio::ip::tcp::resolver::iterator end ;
      boost::asio::ip::tcp::endpoint endpoint;

      while ( destination != end ) {
         endpoint = *destination++;
         std::cout<<endpoint<<std::endl;
      }

      boost::asio::ip::tcp::socket socket(io_service);
      socket.connect(endpoint);
   }
   catch (std::exception& e)
   {
      std::cerr << e.what() << std::endl;
   }
   return 0;
}

我执行了“netstat -l”，它表明我真的在监听我的端口，所以我认为服务器可以正常工作，但绝不会连接不上

服务器代码:

#include <boost/asio.hpp>
#include <iostream>
#include <string>
#include <ctime>
std::string time_string()
{
   using namespace std;
   time_t now = time(0);
   return ctime(&now);
}
int main () {

   try {
      boost::asio::io_service io_service;
      boost::asio::ip::tcp::acceptor acceptor(io_service, boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), 40002));

      for (; ;) {
         std::cout<<"Listening to"<<std::endl;
         boost::asio::ip::tcp::socket socket(io_service);
         acceptor.accept(socket);

         std::string message = time_string();
         boost::system::error_code ignored_error;
         boost::asio::write(socket, boost::asio::buffer(message), boost::asio::transfer_all(), ignored_error);
      }
   }
   catch (std::exception& e)
   {
      std::cerr << e.what() << std::endl;
   }
   return 0;

}

有人可以提示为什么连接没有发生

Answer 1

second parameter ip::tcp::resolver::query 是服务名，不是端口号:

  boost::asio::ip::tcp::resolver::query query("localhost", 40002);

应该是

  boost::asio::ip::tcp::resolver::query query("localhost", "40002");

仅供引用，当我在我的系统上编译你的代码时失败了:

resolve.cc: In function ‘int main()’:
resolve.cc:7: error: invalid conversion from ‘int’ to ‘boost::asio::ip::resolver_query_base::flags’
resolve.cc:7: error:   initializing argument 2 of ‘boost::asio::ip::basic_resolver_query<InternetProtocol>::basic_resolver_query(const std::string&, boost::asio::ip::resolver_query_base::flags) [with InternetProtocol = boost::asio::ip::tcp]’

我很惊讶它是为你编译的。