Boost：反序列化通过 ZeroMQ 拉套接字传递的自定义 C++ 对象

我在这里写的文字是我之前在另一个线程中打开的后续问题Boost：序列化/反序列化通过 ZeroMQ 拉套接字传递的自定义 C++ 对象。早期线程中的编译问题已通过使用文本存档类型而不是二进制存档解决，但现在我在反序列化时遇到运行时问题。为了您的方便，我在这里用新的问题陈述重复之前的文本。我对 C++ 领域比较陌生，感谢任何进一步的帮助。

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 2 - 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3以下。该类的实例化为测试FE.cxx显示在第四个代码片段 below.

GenericMessage实例的接收和反序列化实现在测试BE.cxx可用在第 5 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，然后将其成员打印到标准输出。

问题陈述：

当我运行接收器（即 TestBE.cxx）时，我在这里验证了我可以通过 ZMQ 套接字将数据从 TestFE.cxx 传输到 TEstBE.cxx。但是，当我尝试对 TestBE.cxx 中第 28 行的输入存档进行反序列化时，我得到了下面第一个代码片段中显示的异常（请参阅下面的第五个代码片段，第 28 行已被标记）。

在代码片段 5 的 TestBE.cxx 中实现的反序列化过程中是否缺少某些内容？你认为我为什么会得到这个例外？难道我在 ZMQHandler.cxx 中实现的序列化过程中缺少 st （代码片段 3 - 函数 sendToBE）。提前致谢。

代码片段 1 GDB 输出和回溯

$ gdb TestBE 
GNU gdb (GDB) 7.5-ubuntu
.....
(gdb) r
 Starting program: /TestBE 
 [Thread debugging using libthread_db enabled]
 Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".
 [New Thread 0xb7c12b40 (LWP 16644)]
 [New Thread 0xb7411b40 (LWP 16645)]
 Connecting to FE...

!!!!!!!!!!!!!!!!!!!!!这里开始!!!!!!!!!!!!!!!!!!!!!!!!!!!

 **CHAR [22 serialization::archive 9 0 1 0
 0 1 12 Hello there!]
 terminate called after throwing an instance of 'std::logic_error'
 what():  basic_string::_S_construct null not valid**

!!!!!!!!!!!!!!!!!!!!!这里结束!!!!!!!!!!!!!!!!!!!!!!!!!!!

 Program received signal SIGABRT, Aborted.
 0xb7fdd424 in __kernel_vsyscall ()
 (gdb) bt
 #0  0xb7fdd424 in __kernel_vsyscall ()
 #1  0xb7c7a1df in raise () from /lib/i386-linux-gnu/libc.so.6
 #2  0xb7c7d825 in abort () from /lib/i386-linux-gnu/libc.so.6
 #3  0xb7e608ad in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/i386-  linux-gnu/libstdc++.so.6
 #4  0xb7e5e4f3 in ?? () from /usr/lib/i386-linux-gnu/libstdc++.so.6
 #5  0xb7e5e52f in std::terminate() () from /usr/lib/i386-linux-gnu/libstdc++.so.6
 #6  0xb7e5e825 in __cxa_rethrow () from /usr/lib/i386-linux-gnu/libstdc++.so.6
 #7  0x0804c1d4 in    boost::archive::detail::pointer_iserializer<boost::archive::text_iarchive,    GenericMessage<std::string> >::load_object_ptr (this=0x8054444, ar=..., 
 x=@0x805cb40: 0x805cb50, file_version=0) at    /usr/include/boost/archive/detail/iserializer.hpp:327
 #8  0xb7f3839d in boost::archive::detail::basic_iarchive::load_pointer(void*&,  boost::archive::detail::basic_pointer_iserializer const*,  boost::archive::detail::basic_pointer_iserializer const* (*) (boost::serialization::extended_type_info const&)) () from  /usr/lib/libboost_serialization.so.1.49.0
 #9  0x0804bea9 in    boost::archive::detail::load_pointer_type<boost::archive::text_iarchive>::invoke<GenericMes     sage<std::string>*> (ar=..., t=@0xbfffef70: 0xbfffeff8)
 at /usr/include/boost/archive/detail/iserializer.hpp:524
 #10 0x0804be55 in boost::archive::load<boost::archive::text_iarchive,                                  GenericMessage<std::string>*> (ar=..., t=@0xbfffef70: 0xbfffeff8)
 at /usr/include/boost/archive/detail/iserializer.hpp:592
 #11 0x0804be36 in   boost::archive::detail::common_iarchive<boost::archive::text_iarchive>::load_override<Gener icMessage<std::string>*> (this=0xbfffef84, t=@0xbfffef70: 0xbfffeff8)
  at /usr/include/boost/archive/detail/common_iarchive.hpp:66
 #12 0x0804be14 in  boost::archive::basic_text_iarchive<boost::archive::text_iarchive>::load_override<GenericMe ssage<std::string>*> (this=0xbfffef84, t=@0xbfffef70: 0xbfffeff8)
  at /usr/include/boost/archive/basic_text_iarchive.hpp:65
 #13 0x0804bdf2 in boost::archive::text_iarchive_impl<boost::archive::text_iarchive>::load_override<GenericMes sage<std::string>*> (this=0xbfffef84, t=@0xbfffef70: 0xbfffeff8)
  at /usr/include/boost/archive/text_iarchive.hpp:82
 #14 0x0804bcec in      boost::archive::detail::interface_iarchive<boost::archive::text_iarchive>::operator>> <GenericMessage<std::string>*> (this=0xbfffef84, t=@0xbfffef70: 0xbfffeff8)
 at /usr/include/boost/archive/detail/interface_iarchive.hpp:60
 #15 0x0804b2a1 in main () at TestBE.cxx:28

代码片段 2 (GenericMessage.hxx)

#include <iostream>
#include <string>
#include <sstream>
#include <boost/serialization/serialization.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 Archive>
  void serialize(Archive & ar, const unsigned int version)
  {
      ar & beId;
      ar & data;
  }

 };

代码片段 3 (ZmqHandler.hxx)

#include "zmq.hpp"
#include "GenericMessage.hxx"
#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::ostringstream archive_stream;
   boost::archive::text_oarchive archive(archive_stream);

   try
   {
     archive << theMsg;
   } catch (boost::archive::archive_exception& ex) {
      std::cout << "Archive Exception during deserializing:" << std::endl;
      std::cout << ex.what() << std::endl;           
   } catch (int e) {
       std::cout << "EXCEPTION " << e << std::endl; 
   }

   std::string outbound_data_ = archive_stream.str();
   const char * buf = outbound_data_.c_str();    
   int len = strlen((const char*)buf);
   std::cout << "LENGTH [" << len << "]" << std::endl;

   zmq::message_t msgToSend(len);

   memcpy ((char *) msgToSend.data(), buf, len);

   if(memcmp((char *) msgToSend.data(), buf, len) != 0)
   {
     std::cout << "memcpy error!" << std::endl;
   }

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

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

代码片段 4 (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 5 (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);

       const char *buf = static_cast<const char*>(reply.data());
       std::cout << "CHAR [" << buf << "]" << std::endl;

       std::string input_data_(buf); 
       std::istringstream archive_stream(input_data_);
       boost::archive::text_iarchive archive(archive_stream);
       GenericMessage<std::string> *theMsg;

       try
       {
       /* !!!!!!!!!! LINE 28 is the following !!!!!!!!!!*/
         archive >> theMsg;
       } catch (boost::archive::archive_exception& ex) {
          std::cout << "Archive Exception during deserializing:" << std::endl;
          std::cout << ex.what() << std::endl;           
       } catch (int e) {
          std::cout << "EXCEPTION " << e << std::endl; 
       }

       std::cout << "ID" << theMsg->getBeId() << std::endl; 
       std::cout << "Data" << theMsg->getData() << std::endl; 

     }

    return 0;
   }

你宣布theMsg作为指针（GenericMessage<std::string> *theMsg;).

尝试将该行更改为GenericMessage<std::string> theMsg;.`

异常的真正来源

In the GenericMessage默认构造函数，你初始化data with NULL。但是，您不允许初始化std::string with a NULL指针。不要初始化你的data默认构造函数中的成员。

GenericMessage()
: beId(-1) 
{}

只要你的类型T有一个默认构造函数，编译器将在生成模板时处理其初始化。

（希望）有帮助的提示#1

数据缓冲区在zmq::message_t（通常）不以 NULL 结尾。收到消息后，请注意如何将缓冲区转换为字符串。

// snip
zmq::message_t reply;
socket.recv (&reply);

const char *buf = static_cast<const char*>(reply.data());
std::cout << "CHAR [" << buf << "]" << std::endl;

//std::string input_data_(buf);  // assumes a null-term string
std::string input_data_( buf, reply.size() ); 
// snip

（希望）有帮助的提示#2

另外，我注意到一些东西ZmqHandler.hxx.

// snip
std::string outbound_data_ = archive_stream.str();
const char * buf = outbound_data_.c_str();    
int len = strlen((const char*)buf);
std::cout << "LENGTH [" << len << "]" << std::endl;

zmq::message_t msgToSend(len);

memcpy ((char *) msgToSend.data(), buf, len);

if(memcmp((char *) msgToSend.data(), buf, len) != 0)
{
  std::cout << "memcpy error!" << std::endl;
}
// snip

您不需要检查 memcpy 的结果（除非您想检查其返回值）。整个块可以更改为如下所示：

std::string outbound_data_ = archive_stream.str();
// no need to use the c-style string function 'strlen'
int len = outbound_data_.length();
std::cout << "LENGTH [" << len << "]" << std::endl;

zmq::message_t msgToSend(len);
memcpy( msgToSend.data(), outbound_data_.data(), len );