dynamic_cast到派生类型失败，为什么？

Question

I'd like to have some help on an issue I face.

I'm using serialization (TinyXml to be precise) to save objects in a file and I have a problem on deserialization.

My objects contain pointers, which are not saved directly but instead the ID of the object pointed to is saved.

Every object I save derivate ASerializable, directly or not.

Here is my hierarchy :

//Holds pure virtual method: TiXmlElement * ToXml() = 0;
class ISerializable;

// Basic implementation of ISerializable, this class has a unique ID.
class ASerializable : public ISerializable;

// For security sake, this class is not real, just a demonstration of my problem.
// Overrides TiXmlElement * ToXml()
class Base : public ASerializable;

// Overrides TiXmlElement * ToXml()
class Derived : public Base;

Upon deserialization, I add each object I create into a static map(ID, ASerializable*), which holds the data until dereference.

How I dereference objects

I use a template class which holds a T**, which is the pointer to dereference once all the deserialization is done.

template<typename T>
class Reference<T> {
    T** ref_ptr;
    int id; // This is the ID of the referenced object
    void Dereference();
}

Basically, Reference<T>::Dereference() gets the object in the map, then cast it to the good type (which is T* ) and change the value of *ref_ptr to the cast object.

I'm using dynamic_cast<T*>( objects_map[id] ) to cast my object and for some reason, it fails everytime.

I can't cast from a ASerialisable* to a Derived* without losing the data of Derived .

Here is the pattern I want to achieve :

1. On deserialized, the item add itself to the objects map;

2. If the object is a reference, add a Reference (with the good type, I know it) to a Stack

3. Once all deserialization is done, unstack all references and calls Dereference()

4. Be really happy.

Thank you soooo dor your time and precious help, really appreciated.

{enjoy} EDIT : Okay, I'll try to be clearer, but it is a bit complex.

When I parse my XML file back, there are sometimes element called <reference id="X"> : those are reference to another instance ( ASerializable );

When I encounter a <reference> object, I add it to a stack, to be dereferenced later. When I encounter a specific object, like a <Base id="X" ... data ... /> I build it, then I add it to a object map, as an ASerializable* ;

Once I finished building all my objects, I unstack each of the reference and call Dereference() , that SHOULD go get the REAL INSTANCE of the object, cast it to the good type using dynamic_cast then change the value of his ref_ptr to point that object.

Don't hesitate to ask for other questions if needed.

Answer 1

Does your base class have at least one virtual method? If it has none, make the destructor virtual.

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You might want to look into using Boost.Serialization , it handles serializing to and from XML files nicely.

Answer 2

Alright, thank you all for your time. I found the problem.

Everything was fine in my hierarchy, the problem was a vector that was being copied. The pointers it contained were then changing so my the ref_ptr of Reference was corrupted.

{enjoy}