Re: [Boost-users] [Serialization] Serialize base and derived classes.

Subject: Re: [Boost-users] [Serialization] Serialize base and derived classes.
From: BlueAngel (lists_at_[hidden])
Date: 2010-07-28 18:14:10

Il 28/07/2010 12:38, BlueAngel ha scritto:
> Il 26/07/2010 18:58, BlueAngel ha scritto:
>> Hi lists,
>> I'm working with the Serialization library but I'm having some 
>> troubles with it.
>> The tutorials in the website shown me much but still I need help.
>>
>> I'm using XML archives.
>> I have this classes actually (these classes are all 
>> builders/prototypes, they serialize the datas and then they should 
>> make a new object with those datas):
>> Serializer (an interface, every class which need serialization must 
>> be derived from this, however this is only a marker, it will be not 
>> serialized)
>> RenderableSerializer : public Serializer - this isn't pure virtual 
>> however shouldn't be never serialized directly (since the object made 
>> by this class is a pure virtual one) -  These will use the tag 
>> <renderable>
>> SkyboxSerializer : public RenderableSerializer - these will use the 
>> tag <skybox>
>> EntitySerializer : public Serializer - these will use the tag <entity>
>> many other classes will be added in future and they'll all derive 
>> form RenderableSerializer.
>>
>>
>> Now the problem is EntitySerializer have a pointer to a 
>> RenderableSerializer and when I serialize EntitySerializer the 
>> pointer to that class is considered to be a RenderableSerializer and 
>> not the derived class. I don't know at priori which class is the base 
>> class and this lead to problem.
>> If I serialize a SkyboxSerializer I have the correct tag: a <skybox> 
>> which have inside a <renderable> and the datas are correct.
>> If I try to serialize an Entity I had a lot of problem, mostly just 
>> make the library crash. As I've seen in the tutorial I should 
>> register all the derived classes before pass the pointer to the 
>> Archive. I did it registering the SkyboxSerializer classes but it 
>> lead to a wrong xml: a correct <entity> tag which have a correct 
>> <skybox> with all it's data but also a wrong <renderable> tag which 
>> have inside the same data of the tag <skybox> instead of the data of 
>> a RenderableSerializer class.
>>
>> Now the question is: is there a correct way to use the library this 
>> way? With a pointer to a base class of which the derived is not known?
>> My code is too big and I made many attempt to use the library so I'm 
>> not posting it in this message. If you need it I will post it.
>> Thank you for your replies.
>>
>>
>> _______________________________________________
>> Boost-users mailing list
>> Boost-users_at_[hidden]
>> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> It seems no one know the answer. I hope it's just I made a too vague 
> request. Here's the partial code (load function are implemented the 
> same way, simmetrically):
> EntitySerializer.hpp:
> void *save*(xml_oarchive& ar, const unsigned int version) const
> {
>     ar << make_nvp("EntityName", _nome); // string
>     ar.register_type(static_cast<SkyBoxSerializer *>(NULL)); // Note: 
> this is just for debug, in the future I'll make a function in every 
> class derived from Serializer which register itself when needed.
>     ar << make_nvp(_renderable->getTagName().c_str(), _renderable);
> }
>
> SkyboxSerializer.hpp:
> void *save*(xml_oarchive& ar, const unsigned int version) const
> {
>     ar << make_nvp("renderable",
>         boost::serialization::base_object< RenderableSerializer >(*this));
>     //RenderableSerializer::save(ar, version); // If I use this line 
> instead of the previous it de/serializer correctly but I know this is 
> a dirty work-around and I want to avoid it.
>     ar << make_nvp("shader_file", _fx_file); // std::string
>     ar << make_nvp("mesh_file", _mesh_filename); // std::string
>     ar << make_nvp("cubemap_file", _tex_filename); // std::string
> }
> RenderableSerialier.hpp:
> void *save*(xml_oarchive& ar, const unsigned int version) const
> {
>     ar << make_nvp("scala", _scala); // struct vector
>     ar << make_nvp("rotazione", _rotazione); // struct vector
>     ar << make_nvp("posizione", _posizione); // struct vector
> }
> VectorSerializer.hpp:
> struct vettore
> {
> float x, y, z;
> };
>
> namespace boost
> {
> namespace serialization
>     {
> template<class Archive> void *serialize*(Archive& ar, vettore& vec, 
> const unsigned int version)
>         {
>             ar & make_nvp("x", vec.x);
>             ar & make_nvp("y", vec.y);
>             ar & make_nvp("z", vec.z);
>         }
>     }
> }
>
> Serializer.hpp:
> virtual void *save*(xml_oarchive& ar, const unsigned int version) 
> const = 0;
>
> And this is the xml resultant:
> <?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
> <!DOCTYPE boost_serialization>
> <boost_serialization signature="serialization::archive" version="7">
> <entity class_id="0" tracking_level="0" version="0">
> <EntityName>skybohx</EntityName>
> <skybox class_id="1" tracking_level="1" version="0" object_id="_0">
> <renderable class_id="2" tracking_level="1" version="0" object_id="_1">
> <renderable object_id_reference="_1"></renderable>
> <shader_file>skybox.fx</shader_file>
> <mesh_file>asd.x</mesh_file>
> <cubemap_file>CubeMap.dds</cubemap_file>
> </renderable>
> <shader_file>skybox.fx</shader_file>
> <mesh_file>asd.x</mesh_file>
> <cubemap_file>CubeMap.dds</cubemap_file>
> </skybox>
> </entity>
> </boost_serialization>
>
> As you can see the renderable tag inside the skybox tag is wrong. The 
> <renderable> should have:
> <scala>
> <x>3</x>
> <y>3</y>
> <z>3</z>
> </scala>
> <rotazione>
> <x>2</x>
> <y>2</y>
> <z>2</z>
> </rotazione>
> <posizione>
> <x>1</x>
> <y>1</y>
> <z>1</z>
> </posizione>
>
> Why that tag serialize the derived class instead of itself?
> Thank you again for your answers.
>
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
Hi,
I don't want to insist but... I don't understand:
The:
ar << make_nvp("renderable",
         boost::serialization::base_object< RenderableSerializer >(*this));
of the *save* function of SkyboxSerializer seems to call itself again 
instead of the save function of the RenderableSerializer.
How can this happen?