I have some problems with boost serialization when serializing derived class through base class pointer. I need a system which serializes some objects as they are being received in the system, so I need to serialize over time. This is not really a problem since I can open a boost::archive::binary_oarchive and serialize objects when required. Rapidly I noticed that boost was performing object tracking by memory address, so the first problem was that different objects in time that share the same memory address were saved as the same object. This can be fixed by using the following macro in the required derived class:
BOOST_CLASS_TRACKING(className, boost::serialization::track_never)
This works fine, but again, when the base class is not abstract, the base class is not serialized properly. In the following example, the base class serialization method is only called once with the first object. In the following, boost assumes that this object has been serialized before although the object has different type.
#include <iostream>
#include <fstream>
#include <boost/serialization/export.hpp>
#include <boost/serialization/base_object.hpp>
#include <boost/serialization/list.hpp>
#include <boost/serialization/map.hpp>
#include <boost/serialization/vector.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/archive_exception.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
using namespace std;
class AClass{
public:
AClass(){}
virtual ~AClass(){}
private:
double a;
double b;
//virtual void virtualMethod() = 0;
private:
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
ar & a;
ar & b;
cout << "A" << endl;
}
};
//BOOST_SERIALIZATION_ASSUME_ABSTRACT(Aclass)
//BOOST_CLASS_TRACKING(AClass, boost::serialization::track_never)
class BClass : public AClass{
public:
BClass(){}
virtual ~BClass(){}
private:
double c;
double d;
virtual void virtualMethod(){};
private:
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
ar & boost::serialization::base_object<AClass>(*this);
ar & c;
ar & d;
cout << "B" << endl;
}
};
// define export to be able to serialize through base class pointer
BOOST_CLASS_EXPORT(BClass)
BOOST_CLASS_TRACKING(BClass, boost::serialization::track_never)
class CClass : public AClass{
public:
CClass(){}
virtual ~CClass(){}
private:
double c;
double d;
virtual void virtualMethod(){};
private:
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
ar & boost::serialization::base_object<AClass>(*this);
ar & c;
ar & d;
cout << "C" << endl;
}
};
// define export to be able to serialize through base class pointer
BOOST_CLASS_EXPORT(CClass)
BOOST_CLASS_TRACKING(CClass, boost::serialization::track_never)
int main() {
cout << "Serializing...." << endl;
{
ofstream ofs("serialization.dat");
boost::archive::binary_oarchive oa(ofs);
for(int i=0;i<5;i++)
{
AClass* baseClassPointer = new BClass();
// serialize object through base pointer
oa << baseClassPointer;
// free the pointer so next allocation can reuse memory address
delete baseClassPointer;
}
for(int i=0;i<5;i++)
{
AClass* baseClassPointer = new CClass();
// serialize object through base pointer
oa << baseClassPointer;
// free the pointer so next allocation can reuse memory address
delete baseClassPointer;
}
}
getchar();
cout << "Deserializing..." << endl;
{
ifstream ifs("serialization.dat");
boost::archive::binary_iarchive ia(ifs);
try{
while(true){
AClass* a;
ia >> a;
delete a;
}
}catch(boost::archive::archive_exception const& e)
{
}
}
return 0;
}
When executing this piece of code, the result is as follow:
Serializing....
A
B
B
B
B
B
C
C
C
C
C
Deserializing...
A
B
B
B
B
B
C
C
C
C
C
So the base class is only being serialized once, although the derived class has explicitly the track_never flag. There are two different workarounds to fix this behaviour. The first one is to make the base class abstract with a pure virtual method and calling the macro BOOST_SERIALIZATION_ASSUME_ABSTRACT(Aclass), and the second one is to put the track_never flag also in the base class (commented in code).
None of these solutions meets my requirements, since I want to do in the future punctual serializations of the system state, which would require tracking features for a given DClass extending A (not B or C), and also the AClass should not be abstract.
Any hints? Is there any way to call explicitly the base class serialization method avoiding the tracking feature in the base class (that already has been disabled in the derived class)?
