Boost：序列化/反序列化通过 ZeroMQ 拉套接字传递的自定义 C++ 对象

描述：

我有一个名为的 C++ 类通用消息它仅保存一个 id 和数据作为其成员（请参阅下面的代码片段 1 - GenericMessage.hxx）。我的目的是序列化此类的实例并通过实现推送模式的 ZeroMQ 套接字发送它。

序列化和发送任务已实现类 ZMQHandler（参见sendToBE函数）它被放置在一个名为ZMQHandler.hxx的头文件中，如图所示代码片段2以下。该类的实例化为测试FE.cxx显示在第三个代码片段 below.

GenericMessage实例的接收和反序列化实现在测试BE.cxx可用在第四个代码片段以下。我的目的是通过 ZMQ 套接字（即拉套接字）接收 GenericMessage 实例，对其进行反序列化，然后打印其成员。

Problem:

问题是，当我编译 TestBE.cxx 时，出现许多涉及模板函数的编译错误。考虑到 TestBE.cxx 中的代码，谁能告诉我在第四个代码片段中标有注释的反序列化部分中缺少什么？我是一个相对较新的 C++ 程序员，想知道如何解释这些与模板函数相关的编译错误，这些错误已列在本文底部（即最终片段）。第 18 行是编译错误发生的地方，在第 4 个代码片段中进行了标记。谢谢。

代码片段 1 (GenericMessage.hxx)

#include <iostream>
#include <string>
#include <sstream>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>

template <class T>
class GenericMessage {
public:
      GenericMessage(): 
      beId(-1), data(NULL)
      {}

      GenericMessage(int id, T msg): beId(id), data(msg)
      {}

     ~GenericMessage(){}

     T getData()
     {
       return data;
     }


     std::string toString()
     {
        std::ostringstream ss;
        ss << getBeId();
        std::string ret =  ss.str();

        return ret;
      }

      void setBeId(int id)
      {
        beId = id;
      }

      int getBeId()
      {
        return beId;
      }


      private:
            friend class boost::serialization::access;

            int beId;
            T data;

            template <class Archieve>
            void serialize(Archieve & ar, const unsigned int version)
            {
               ar & beId;
               ar & data;
            }

 };

代码片段 2 (ZMQHandler.hxx)

 #include "zmq.hpp"
 #include "GenericMessage.hxx"
 #include <pthread.h>
 #include <unistd.h>
 #include <cassert>

template <class A>
class ZmqHandler {
public:

       ZmqHandler():
   mContext(1),
   mOutbHandlerSocket(mContext, ZMQ_PUSH)
       {    
            mOutbHandlerSocket.bind ("tcp://*:5555");       
       }

       ~ZmqHandler() {}

        void sendToBE(GenericMessage<A> &theMsg)
        {
           std::stringstream ss(std::ios_base::binary| std::ios_base::out|  std::ios_base::in);
           boost::archive::binary_oarchive oa(ss, boost::archive::no_header);
           oa << theMsg;

           zmq::message_t msgToSend(sizeof(ss));

           memcpy(msgToSend.data(), ss.str().data(), ss.str().length());
           if(memcmp(msgToSend.data(), ss.str().data(), ss.str().length()) != 0)
           {
               printf("memcpy error\n");
           }

           mOutbHandlerSocket.send(msgToSend);
           std::cout << "SENT request: [" << theMsg.toString() << "]" << std::endl;
}   

    private:  
          zmq::context_t mContext;
          zmq::socket_t mOutbHandlerSocket;         
};

代码片段 3 (TestFE.cxx)

 #include "ZmqHandler.hxx"

 int main ()
 {
   ZmqHandler<std::string> zmqHandler;
   int counter = 1;

   while(1)
   {  
     std::string data = "Hello there!\0";
     GenericMessage<std::string> msg(counter, data);
     zmqHandler.sendToBE(msg);
     counter++;
     sleep(1);
    }

    return 0;
 }     

代码片段 4 (TestBE.cxx)

 #include "zmq.hpp"
 #include "GenericMessage.hxx"
 #include <fstream>

 int main ()
 {
    //  Prepare our context and socket
    zmq::context_t context (1);
    zmq::socket_t socket (context, ZMQ_PULL);

   std::cout << "Connecting to FE..." << std::endl;
   socket.connect ("tcp://localhost:5555");

   while(1){
       zmq::message_t reply;
       socket.recv (&reply);

       /* !!!!!!! LINE 18 starts HERE !!!!!!! */
       std::stringstream is(reply.data(), std::ios_base::binary| std::ios_base::out| std::ios_base::in);
       boost::archive::binary_iarchive ia(is, boost::archive::no_header);

       GenericMessage<std::string> msg;
       ia >> msg;

       std::cout << "RECEIVED: " << msg.toString() << std::endl;
       std::cout << "DATA: " << ((std::string)msg.getData())  << std::endl;
    }

     return 0;
 }

TestBE.cxx 的编译输出

 g++ -g -c TestBE.cxx GenericMessage.hxx
 TestBE.cxx: In function ‘int main()’:
 TestBE.cxx:18:104: error: invalid user-defined conversion from ‘void*’ to ‘const  __string_type& {aka const std::basic_string<char>&}’ [-fpermissive]
       In file included from /usr/include/c++/4.7/string:55:0,
             from /usr/include/c++/4.7/bits/locale_classes.h:42,
             from /usr/include/c++/4.7/bits/ios_base.h:43,
             from /usr/include/c++/4.7/ios:43,
             from /usr/include/c++/4.7/ostream:40,
             from /usr/include/c++/4.7/iostream:40,
             from GenericMessage.hxx:1,
             from TestBE.cxx:2:
  /usr/include/c++/4.7/bits/basic_string.tcc:214:5: note: candidate is:     std::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&)  [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>] <near  match>
  /usr/include/c++/4.7/bits/basic_string.tcc:214:5: note:   no known conversion for argument 1 from ‘void*’ to ‘const char*’
  TestBE.cxx:18:104: error: invalid conversion from ‘void*’ to ‘const char*’ [-fpermissive]
       In file included from /usr/include/c++/4.7/string:55:0,
             from /usr/include/c++/4.7/bits/locale_classes.h:42,
             from /usr/include/c++/4.7/bits/ios_base.h:43,
             from /usr/include/c++/4.7/ios:43,
             from /usr/include/c++/4.7/ostream:40,
             from /usr/include/c++/4.7/iostream:40,
             from GenericMessage.hxx:1,
             from TestBE.cxx:2:
       /usr/include/c++/4.7/bits/basic_string.tcc:214:5: error:   initializing argument 1 of ‘std::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ [-fpermissive]
       make: *** [TestBE.o] Error 1

我想说错误消息非常清楚：字符串流的构造函数 http://www.cplusplus.com/reference/sstream/stringstream/stringstream/需要任一类型openmode or std::string，并且您传递了一个类型的参数void*（返回reply.data()).

您可以将收到的消息转储到二进制文件中，但您仍然需要进行一些转换。