How to use destructors on arrays of derived objects?

Question

I have a three theoretical questions regarding virtual destructors: lets assume I have a base class Base - two derived classes Derivative_1 and Derivative_2 , class Stand_Alone and class Project . class Stand_Alone is used aa private member both in Base and Project . class Project has the private members: objects of Derivative_1 , a dynamic array of Derivative_2 objects and a Stand_Alone object. for the example lets assume that only one Project object is created in the main.

1. is the destructor of Project correct - de-allocating all dynamic memory of an object?
2. should the destructor of Base be declared as virtual ?
3. the destructors of Derivative_1 and Derivative_2 shouldn't be declared as virtual , right?

thanks.

#ifndef PROJECT_H
#define PROJECT_H
#include "Stand_Alone.h"
#include "Derivative_1.h"
#include "Derivative_2.h"

class Project
{
public:
    Project();
    ~Project()
{
    delete [] support;
    support = NULL;
}
 protected:
 private:
    Stand_Alone member;
    Derivative_1 head;
    Derivative_2 *support;
};

#endif // PROJECT_H

Answer 1

1. is the destructor of Project correct - de-allocating all dynamic memory of an object?

Yes, although there are safer ways of doing that. You could declare a vector of Derivative_2 objects instead of manipulating the memory yourself. This way you wouldn't need to declare a destructor at all, since the default destructor provided by your compiler would do the job pretty well.

1. should the destructor of Base be declared as virtual ?

Yes, this is the only way to make sure that it will be called when objects of either its subclasses are destroyed.