Re: [Boost-users] [Serialization] Problem serializing via baseclass ptr

From: Robert Ramey (ramey_at_[hidden])
Date: 2006-07-18 12:15:42

Hmm - looks like it should work to me.

I would try the following:

a) make a tiny test - a main which which does nothing but tests the 
serialization.
This you can ship to us in necessary.
b) For now - remove all the BOOST_CLASS_TRACKING macros.
It shouldn't make a difference but let's start simple.
c) You'll have to add BOOST_CLASS_EXPORT for SomeData
d) double check that everything is in the same namespace.
e) try removing the friend class boost::serialization::access; from
the base class.  NonVolatileData::serialize(..) should never be called
by the serialization library in this case - so if this traps during compile,
it will show a chain of "compile time calls".  By looking at this chain
one can see where things went wrong.  Unfortunately this requires
looking at the header source code - oh well.
f) double check that the test corresponding to your example builds
and runs in your environment.  If that passes, but yours does not, try
modifying the test bit by bit by commenting out the code that is there
and replacing it with your own code.  If you finish this and the test
still works - then just remove all the commented code and you'll be
done.

Robert Ramey

Guy Létourneau wrote:
> Robert,
> I've tried to include your changes but it doesn't solve the problem.
> I had to add the following line: BOOST_IS_ABSTRACT(NonVolatileData)
> for the program to compile.  I agree with you, to have an abstract
> class is what is needed in that case as the NonVolatileData class is
> not intended to do something useful except for allowing my data
> storage layer to be generic.  However, abstract or not, I still have
> the same problem: when serializing my SomeData object through a
> pointer to the NonVolatileData, only the data of the parent class
> gets serialized.  Anything else you want me to try?
>
> Thanks,
> Guy
>
>> Try making the base class polymorphic - that it define at least
>> one abstract function. See my changes below. This will have
>> the beneficial effect of inhibiting anyone from creating an instance
>> of your base class directly.
>> Robert Ramey
>
>> Guy Létourneau wrote:
>>> Hello,
>>>
>>> I need to develop a generic data storage layer. Its job is to handle
>>> the serialization of all objects that need to be persistent in my
>>> system and handle management of archives, backups and restores and
>>> so forth. The most important point is that it must stay generic,
>>> i.e. have no knowledge of the type of objects being passed by other
>>> modules in the system. Because of this, I define a base class
>>> NonVolatileData from which all data classes in the system will
>>> derive:
>>>
>>> ///////////////////////////////////////////////////////////////////////
>>> // Base class
>>> class NonVolatileData
>>> {
>>> friend
>>> class boost::serialization::access;
>>>
>>> public:
>>>
>>> NonVolatileData(){ i = 1; };
>>> virtual ~NonVolatileData() = 0; // Note - pure virtual function
>>> make class abstract-
>>>
>>>
>>> protected:
>>>
>>> virtual void Dummy() =0; // Note - pure virtual function make
>>> class abstract-
>> ;
>>>
>>> int i;
>>> template <class Archive>
>>> void serialize( Archive& ar, const unsigned int version )
>>> {
>>> ar & i;
>>> }
>>> };
>>> BOOST_CLASS_TRACKING(NonVolatileData,
>>> boost::serialization::track_never)
>>>
>>>
>>> class SomeData: public NonVolatileData
>>> {
>>> friend
>>> class boost::serialization::access;
>>>
>>> public:
>>>
>>> SomeData ()
>>> {
>>> };
>>>
>>> ~SomeData ()
>>> {
>>> };
>>>
>>> void SetValue( std::string& Address )
>>> {
>>> this->Address = Address;
>>> }
>>>
>>> void Dummy()
>>> {
>>> }
>>>
>>> private:
>>>
>>> template <class Archive>
>>> void serialize( Archive& ar, const unsigned int version )
>>> {
>>> ar &
>>>
>>> boost::serialization::base_object<NonVolatileData>(*this);
>>> ar& Address; }
>>>
>>> std::string Address;
>>> };
>>> BOOST_CLASS_TRACKING(SomeData, boost::serialization::track_never)
>>> /////////////////////////////////////////////////////////////////
>>>
>>> My data storage interface will take a ptr to the base class i.e.
>>> Save(NonVolatileData* data) so the serialization will be performed
>>> through a ptr to the base class. I've read the documentation
>>> multiple times and I'm still unable to make that work correctly.
>>> When a do a save, only the base class is serialized even though the
>>> base class is polymorphic. I've tried using the
>>> BOOST_CLASS_EXPORT_GUID macro the force a registration of my derived
>>> class without success. I've also checked the example from demo.cpp.
>>> It uses the direct call to register_type() but in my case, I don't
>>> want to change the code everytime a new class is defined in the
>>> system so I went with option 2 (the macro). There's probably a
>>> subtle detail I do not do correctly (polite way of saying I'm
>>> missing something :-)).
>>>
>>> Thanks for your help,
>>>
>>> Guy Letourneau =