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

17 Jul 2006


      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