在Boost ASIO服务器和Java客户端之间通过TCP发送Double

Question

我试图用一个Java客户机建立一个简单的Boost ASIO服务器。

我能够发送和成功接收字符串之间的两个。然而，当我试图发送双值时，只有垃圾在另一端出来。

下面是显示基本设置的独立代码（使用C++Boost ASIO服务器和Java客户端）。当它们运行时,它们执行以下四个顺序任务：

null

#include <iostream>
#include <string>

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

using boost::asio::ip::tcp;

int main()
{
   unsigned short const PORT = 19876;

   try
   {
      boost::asio::io_service ioService;
      tcp::acceptor acceptor(ioService, tcp::endpoint(tcp::v4(), PORT));

      while (true)
      {
         // Listen for clients
         std::cout << "Listening for client..." << std::endl;
         tcp::socket socket(ioService);
         acceptor.accept(socket);
         std::cout << "Client heard..." << std::endl;

         size_t len;

         // Receive string from client and print it out
         boost::array<char, 128> cBuf;
         len = socket.read_some(boost::asio::buffer(cBuf, sizeof(cBuf)));
         std::cout.write(cBuf.data(), len);

         // Send string to client
         std::string message = "Server string to send to client\n";
         boost::asio::write(socket, boost::asio::buffer(message));

         // Receive double from client and print it out
         double dVal1 = -1.0;
         char * p_dVal1 = reinterpret_cast<char *>(&dVal1);
         len = socket.read_some(boost::asio::buffer(p_dVal1, sizeof(double)));
         std::cout << dVal1<< std::endl; // prints out garbage

         // Send double to client
         double dVal2 = 6.28;
         char const * p_dVal2 = reinterpret_cast<char const *>(&dVal2);
         boost::asio::write(socket, boost::asio::buffer(p_dVal2, sizeof(double)));
      }
   }
   catch (std::exception & e)
   {
      std::cerr << e.what() << std::endl;
   }

   return 0;
}

import java.io.*;
import java.net.*;

public class Client
{
    final static String HOST = "localhost";
    final static int    PORT = 19876;

    public static void main(String[] args) throws IOException
    {
        Socket socket = new Socket(HOST, PORT);

        // Send string to server
        PrintWriter pos = new PrintWriter(socket.getOutputStream(), true);
        pos.println("Client string to send to server");

        // Receive string from server
        BufferedReader bis =
            new BufferedReader(new InputStreamReader(socket.getInputStream()));
        System.out.println(bis.readLine());

        // Send double value to server
        DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
        dos.writeDouble(3.14);

        // Receive double from server
        DataInputStream dis = new DataInputStream(socket.getInputStream());
        System.out.println(dis.readDouble()); // prints out garbage

        socket.close();
        pos.close();
        bis.close();
        dos.close();
        dis.close();
    }
}

Answer 1

您需要使用lexical_cast，而不是reinterpret_cast。

使用reinterpret_cast，您告诉编译器将double*位模式直接解释为常量字符*位模式。相反，您的强制转换应该使用ascii字符创建一个新结构，以ascii位模式表示数字。

此外，您应该确保您正在管理Endianess。您应该正确地在客户端和服务器上进行网络endianess的转换和从网络endianess的转换。有关其他信息，请参阅此答案。