boost serialization of polymorph classes from DLLs

M

MindWrapper

boost serialization of polymorph classes from DLLs

Folks,

Let's consider following code
--------------------------------
// base.h
// abstract base class
class IBase
{
}

BOOST_IS_ABSTRACT(IBase)
--------------------------------



---------------------------
class derived : public IBase
{
friend class boost::serialization::access;

template <class Archive>
void serialize(Archive & ar, const unsigned int version )
{
//...
}
}


BOOST_CLASS_EXPORT_GUID(derived, "derived ");

---------------------------



Main application knows only about IBase and it dynamically loads dll
where class derived is defined. Dll exports some method to create
instance of derived :

---------------------------
IBase* extern "C" __declspec(dllexport)
create(IShapesFactory* pfactory)
{
return new Derived;
};
---------------------------

What I want to figure out is that possible to serialize polymorphic
pointer received in such way


Something like that:

std::eek:fstream ofs("file");
boost::archive::text_oarchive oa(ofs);


IBase* p;
// initialize p using above exported method. So, p points to derived
instance.
oa & p; // ???


As I understood this is in principle impossible, because for each
combination of type and archive following template declared in boost
library must be instantiated

template<class Archive, class T>
inline void serialize(
Archive & ar,
T & t,
const unsigned int file_version
){
// invoke member function for class T
t.serialize(ar, file_version);
}

So for main application template instantiation is not available?


Does anyone have another opinion?


Thank you!
 
A

Abhishek Padmanabh

boost serialization of polymorph classes from DLLs

Folks,

Let's consider following code
--------------------------------
// base.h
// abstract base class
class IBase
{

}

BOOST_IS_ABSTRACT(IBase)
--------------------------------

---------------------------
class derived : public IBase
{
friend class boost::serialization::access;

template <class Archive>
void serialize(Archive & ar, const unsigned int version )
{
//...
}

}

BOOST_CLASS_EXPORT_GUID(derived, "derived ");

---------------------------

Main application knows only about IBase and it dynamically loads dll
where class derived is defined. Dll exports some method to create
instance of derived :

---------------------------
IBase* extern "C" __declspec(dllexport)
create(IShapesFactory* pfactory)
{
return new Derived;};

---------------------------

What I want to figure out is that possible to serialize polymorphic
pointer received in such way

Something like that:

std::eek:fstream ofs("file");
boost::archive::text_oarchive oa(ofs);

IBase* p;
// initialize p using above exported method. So, p points to derived
instance.
oa & p; // ???

As I understood this is in principle impossible, because for each
combination of type and archive following template declared in boost
library must be instantiated

template<class Archive, class T>
inline void serialize(
Archive & ar,
T & t,
const unsigned int file_version
){
// invoke member function for class T
t.serialize(ar, file_version);

}

So for main application template instantiation is not available?

Does anyone have another opinion?

You would be better off posting this to the boost mailing lists.

But, you are right. For your main application, the template function
serialize will not be available because the class and its own
serialization infrastructure lies in the dll loaded dynamically. And
that DLL does not know what archive is to be used because the
serialization would be invoked from the main app.

Since you say that the main application has no knowledge of the
various derived classes, the only option that I see is the DLL
providing the serialization functionality on its own. Can you have
serialize/deserialize functions exported from the DLL that use one (or
as many you wish to support) of the archive types (text/xml/binary)
and the dll has the complete responsibility thereon for the
serialization/deserialization? I am not very sure if that would be
possible but if yes, it still would suffer from the limitation on the
set of supported archive types.
 

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