Re: [Boost-users] [serialization] polymorphic archives in dlls andpointer to derived problems

Subject: Re: [Boost-users] [serialization] polymorphic archives in dlls andpointer to derived problems
From: Robert Ramey (ramey_at_[hidden])
Date: 2011-01-04 13:29:15

Kolb, Jeremy wrote:
> I'm having a lot of trouble getting serialization of derived classes
> through a base pointer working across dlls.

Take a look at dll_polymorphic_derived2 in the serialization test directory.
The suggested changes are as follows:

  I have the following:
>
> DLL (data_types.dll) code:
>

// delete global includes
> stdafx.h:
> #pragma once
>
> #include "targetver.h"
>
> #define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff
> from Windows headers
> // Windows Header Files:
> #include <windows.h>
>

// base doesn't have to be exported
> Base.h:
> #pragma once
> class __declspec(dllexport) Base
> {
>     friend class boost::serialization::access;
>     template<class Archive> void serialize(Archive& ar, const
> unsigned int version);
>
> public:
>     Base() {}
>     virtual ~Base() {}
>     int i;
> };
>
> BOOST_SERIALIZATION_ASSUME_ABSTRACT(Base); // Doesn't make a
> difference.

// base serialization needs to be instantiated for all archives to be used
> Base.cpp:
> #include "stdafx.h"
> #include "Base.h"
>
> template<class Archive>
> void Base::serialize(Archive& ar, const unsigned int version)
> {
>     ar & BOOST_SERIALIZATION_NVP(i);
> }

// instantiate for the "real" archives used - that is 
polymorphic_text_iarchive, etc.
// note that I don't believe that this should be necessary for abstract base 
class Base.
// So first try totally excluding this.

> template void __declspec(dllexport)
> Base::serialize(boost::archive::polymorphic_xml_iarchive& ar, const
> unsigned int version);
> template void __declspec(dllexport)
> Base::serialize(boost::archive::polymorphic_xml_oarchive& ar, const
> unsigned int version);

// be sure to include any other archives which might be used (text, binary, 
etc)

// Derived classes MUST be exported.
>
> Derived.h:
> #include "Base.h"
>
> class __declspec(dllexport) Derived : public Base
> {
>     friend class boost::serialization::access;
>     template<class Archive> void serialize(Archive& ar, const
> unsigned int version);
>
> public:
>     Derived() {}
>     Derived(int num) : j(num) {}
>     int j;
> };
>
> BOOST_CLASS_EXPORT_KEY(Derived);
>

> Derived.cpp:
> #include "stdafx.h"
> #include "Derived.h"
>
> template<class Archive>
> void Derived::serialize(Archive& ar, const unsigned int version)
> {
>     ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(Base);
>     ar & BOOST_SERIALIZATION_NVP(j);
> }
>
> BOOST_CLASS_EXPORT_IMPLEMENT(Derived);

// instantiate for the "real" archives used - that is 
polymorphic_xml_iarchive, etc.

> template void __declspec(dllexport)
> Derived::serialize(boost::archive::polymorphic_xml_iarchive& ar, const
> unsigned int version);
> template void __declspec(dllexport)
> Derived::serialize(boost::archive::polymorphic_xml_oarchive& ar, const
> unsigned int version);

> My exe links against the DLL and contains the following:

// should run

> #include "stdafx.h"
> #include "boost/archive/polymorphic_xml_iarchive.hpp"
> #include "boost/archive/polymorphic_xml_oarchive.hpp"
>
> #include "data_types/Derived.h"
> #include <fstream>
>
> int _tmain(int argc, _TCHAR* argv[])
> {
>     std::ofstream f("c:\\test.xml");
>     boost::archive::polymorphic_xml_oarchive xml(f);
>
>     Base* b = new Derived(123);
>     xml & BOOST_SERIALIZATION_NVP(b);
>
>     delete b;
>
>       return 0;
> }

Robert Ramey