[Boost-users] [serialization] problem exporting derived classes

Subject: [Boost-users] [serialization] problem exporting derived classes
From: Jens Weggemann (bravestar_at_[hidden])
Date: 2009-02-18 19:15:07

Hello,

I've been trying out boost::serialization and ran into a problem
trying to serialize objects of derived classes.
I set up this simple class hierarchy:

class BaseNode {
  std::vector<BaseNode*> children_;
  ...
  friend class boost::serialization::access;
  template<class Archive>
  void serialize(Archive &ar, unsigned version) {
    ar & children_;
  }
};
class DerivedNode : public BaseNode
{
  ...
  friend class boost::serialization::access;
  template<class Archive>
  void serialize(Archive &ar, unsigned version) {
    ar & boost::serialization::base_object<BaseNode>(*this);
  }
};

All works fine as long as I register the types with the archives:

arch.register_type(static_cast<BaseNode*>(NULL));
arch.register_type(static_cast<DerivedNode*>(NULL));

Now the documentation suggests exporting the classes as an alternative 
to that. But when I instead put

BOOST_CLASS_EXPORT(BaseNode)
BOOST_CLASS_EXPORT(DerivedNode)

the polymorphism is not handled correctly and e.g. a tree of 3
DerivedNodes is restored as a single BaseNode object.
What am I missing here?

The full code for this test is at 
http://noonti.de/tree_serialization.cpp.txt

Thanks,

Jens