[Boost-users] Re: Serialization when using virtual inheritance

29 May 2005

      This should should work but it requires that derived types be either
"registered" or "exported".  This is eplained in the manual under
serialization of pointers and under serialization traits.  Basically you
need either:

class Base
{
virtual void OneOfManyVirtuals() = 0;
// Serialization Interface
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
//empty
    ar.register<Derived>(); // for each derived class
}

Or for each derived class (in its own header):

BOOST_CLASS_EXPORT(Derived)

That will solve the problem.

Robert Ramey

Eric wrote:
...
Boost version:  1.32.0
I am trying to use the serialization class to serialize data pointed
to by the virtual base class. Note that the code works great if I
don't use virtual inheritance off of the base class. Here is a quick
run-down of the hierarchy and code:
class Base
{
virtual void OneOfManyVirtuals() = 0;
// Serialization Interface
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
//empty
}
};
BOOST_IS_ABSTRACT(Base);
class Derived : virtual public Base
{
virtual void OneOfManyVirtuals() { }
// Serialization Interface
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
//empty
ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(Base);
}
}
// later in the main code
Base* pBase = new Derived;
boost::archive::xml_oarchive oa(ofs);
// doesn't work
oa << BOOST_SERIALIZATION_NVP(pBase);
// works
oa << BOOST_SERIALIZATION_NVP(*pBase);
When if fails, it fails in the oseralizer.hpp at line 419 with the
comment: // convert pointer to more derived type. if this is thrown
// it means that the base/derived relationship hasn't be registered
I tried registering the pairs with void_cast_register, but I wasn't
successful. Any real examples of how to use this method would be
appreciated.
So, does anyone know why the pointer to the base doesn't work when
using virtual inheritance? It works find when I remove the virtual
from the inheritance. Unfortunately, with the software architecture
that I have, there are several cases when the virtual inheritance off
of interfaces is required.
Any help with the matter is greatly appreciated.
-Eric