Invoking a virtual method from a destructor - a workaround?

Question

I need to declare a finalize() finalization method for all descendants of the Base base class that should be called at the time of destruction, and my intention was to call pure virtual void Base::finalize() = 0 from ~Base() , but C ++ forbids such a thing. So my question is:

How can we get descendants to do some final work in a right and predefined way?

This code cannot be compiled:

 #include <QDebug> class Base { public: Base(){} virtual ~Base(){ qDebug("deleting b"); finalize(); } virtual void finalize() = 0; }; class A : public Base { public: A(){} ~A(){} void finalize(){qDebug("called finalize in a");} }; int main(int argc, char *argv[]) { Base *b = new A; delete b; } 

If I make Base::finalize() not pure virtual, it is called from ~Base() without sending it to the child, since it has already been destroyed.

I can call finalize () from the child destructor, but the question is how to get this done. In other words, my question is: is it possible to oblige people who will write descendants of the base class to use the finalization method, well, differently than to comment on it in the documentation? :)

Answer 1

Destructors are the right place to free up acquired resources, but each class is responsible for releasing its resources. Resources obtained with class A should not (and simply cannot) be freed by class Base .

Defining virtual destructors allows you to call the class A destructor when you delete a pointer to a class Base that points to a class A object

 Base* p = new A; delete p; // Both A and Base destructors are sequencially called! 

So, in order to achieve the proper release of resources, you just need to free the resources of each class in your own destructor.

Answer 2

For a virtual destructor:

 class A { public: virtual ~A() {} }; class B : public A { public: virtual ~B() {} }; 

When an object of type B destroyed, whether the pointer to B or the pointer to A is called, both destructors will be called. First B::~B() , and then A::~A() .

Answer 3

Make the base class destructor pure virtual with the body, which should do exactly what you want.

Answer 4

Why not use a base descriptor? What are destructors intended for?

Do a RAII search and find one of the best things in C ++.

Most people using other languages ​​should find this out. Resource management in C ++ is completely different from most other computer languages.