[boost] [serialization] exception during deserialization

7 May 2004

      I am trying to use the serialization library to save an object and a 
pointer to the object, but the pointer has the type of the object's base 
class. Something like:

// declaration
MyClass myObject;	// object, not pointer
MyBaseClass *myPointer = &myObject;

// serialization code
ar & BOOST_SERIALIZATION_NVP(myObject);
ar & BOOST_SERIALIZATION_NVP(myPointer);

And I get an exception (either null reference exception or access 
violation) during the deserialization. I am using xml archives. The xml 
generated code seems fine.

I have also noticed that saving a pointer of the object's type pointing 
to the object solves the problem:

// updated code
MyClass myObject;	// object, not pointer
MyClass *myOtherPointer = & myObject
MyBaseClass *myPointer = &myObject;

// serialization code
ar & BOOST_SERIALIZATION_NVP(myObject);
ar & BOOST_SERIALIZATION_NVP(myOtherPointer);
ar & BOOST_SERIALIZATION_NVP(myPointer);

So is it a bug, or have I done something wrong ?
The compiler is VC7.1, full example code is in attachement.

Thanks,
Francois Fath

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#include "stdafx.h"
#include <fstream>
#include <boost/archive/xml_oarchive.hpp>
#include <boost/archive/xml_iarchive.hpp>
#include <boost/serialization/export.hpp>

using namespace std;

/*
 * Base class
 */
class Base
{
public:
	Base() {}
	virtual ~Base() {}

private:
	friend class boost::serialization::access;
    template<class Archive> void serialize(Archive & ar, const unsigned int version)
    {
    }
};

/*
 * Derived class
 */
class Derived : public Base
{
public:
	Derived() {}
	virtual ~Derived() {}

private:
	friend class boost::serialization::access;
    template<class Archive> void serialize(Archive & ar, const unsigned int version)
    {
		ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(Base);
/* uncomment to avoid the exception
 *		ar & BOOST_SERIALIZATION_NVP(this);
 */
    }
};

/*
 * exports
 */
BOOST_CLASS_EXPORT(Base)
BOOST_CLASS_EXPORT(Derived)

int _tmain(int argc, _TCHAR* argv[])
{
	// create
	Derived derived;
	Base *base = &derived;

	// serialize
	{
		ofstream ofs("toto.xml");
		boost::archive::xml_oarchive oa(ofs);
		oa << BOOST_SERIALIZATION_NVP(derived);
		oa << BOOST_SERIALIZATION_NVP(base);
	}

	// deserialize
	{
		ifstream ifs("toto.xml");
		boost::archive::xml_iarchive ia(ifs);
		ia >> BOOST_SERIALIZATION_NVP(derived);
		ia >> BOOST_SERIALIZATION_NVP(base);
	}

	//quit
	return 0;
}

[boost] [serialization] exception during deserialization

FATH Francois