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

Question

我在这里写的文字是我之前在Boost: Serializing/De-serializing a custom C++ object passed over ZeroMQ pull socket 的另一个线程中打开的后续问题。早期线程中的编译问题已通过使用 textarchive 类型而不是 binaryarchive 解决，但现在我在反序列化时遇到运行时问题。为方便起见，我在这里用一个新的问题陈述重复前面的文本。我对 C++ 领域还比较陌生，如果有任何进一步的帮助，我将不胜感激。

说明：

我有一个名为 GenericMessage 的 C++ 类，它只包含一个 id 和数据作为其成员（参见下面的代码 sn-p 2 - GenericMessage.hxx）。我的意图是序列化这个类的一个实例，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经在class ZMQHandler中实现（见sendToBE函数），它被放置在code sn-p 3所示的头文件名ZMQHandler.hxx中强>下面。此类由 TestFE.cxx 实例化，如下面的第 4 段代码 sn-p 所示。

GenericMessage 实例的接收和反序列化在TestBE.cxx 中实现，可在下面的5th code sn-p 中找到。我的意图是通过 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，当我尝试反序列化 TestBE.cxx 中第 28 行的输入存档时，我得到了下面第一个代码 sn-p 中显示的异常（请参见下面的第 5 个代码 sn-p，第 28 行已标记） .

在代码 sn-p 5 中的 TestBE.cxx 中实现的这个反序列化过程中我缺少什么吗？为什么你认为我得到这个例外？可能是我在 ZMQHandler.cxx 中实现的序列化过程中缺少 st（代码 sn-p 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;
   }

Answer 1

您将 theMsg 声明为指针 (GenericMessage<std::string> *theMsg;)。

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

异常的真正来源

在GenericMessage 默认构造函数中，使用NULL 初始化data。但是，不允许使用 NULL 指针初始化 std::string。不要在默认构造函数中初始化 data 成员。

GenericMessage()
: beId(-1) 
{}

只要你的类型T有一个默认构造函数，编译器就会在模板生成时处理它的初始化。

（希望）有用的提示 #1

zmq::message_t 中的数据缓冲区（通常）不是以 NULL 结尾的。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）有用的提示 #2

另外，我注意到 ZmqHandler.hxx 中有一些内容。

// 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

你不需要检查 memcpy 的结果（除非你想检查它的返回值）。整个块可以改成这样：

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 );