How much is deleted when you delete a class or struct in c++?

Question

This is just an idle thought I had when reading this other question:

What is the correct way to delete char**

If the chars mentioned in that question had been created inside an object and that object was deleted, would that correctly clean up the pointers as well, or would they be stuck in memory?

Answer 1

If you delete an object, the destructor for that object will be called, so you need to do a delete in the destructor. So remember, everything that the class has allocated on the heap has to be freed in the destructor. If it was been allocated on the stack this happens automatically

struct A
{
    A() { std::cout << "A()" << std::endl; ptr = new char[10]; }
    ~A() { std::cout << "~A()" << std::endl; delete []ptr; }
    char *ptr;
};

But be careful, if you are using inheritance, if A inherits from a base class, you need to make the base destructor virtual, or else the destructor in A will not be called and you will have a memory leak.

struct Base
{
    virtual ~Base() {}
};

struct A : public Base
{
    A() { std::cout << "A()" << std::endl; ptr = new char[10]; }
    ~A() { std::cout << "~A()" << std::endl; delete []ptr; }
    char *ptr;
};

Answer 2

They would stuck in the memory. Therefore you need to define Destructor when you make dynamic memory allocation within objects. The D'tor is called when the parent object is about to be delete, and you should explicitly free in the D'tor all the sub-allocated memory.

For more info, look at Wikipedia.