Question

The following code creates a double pointer B** to a B*. It’ll use that pointer to allocate memory for another pointer which will point to a B instance created when start() is called:

class A:

class A
{
public:
    A()
    {
        fb = new B*;
        *fb = NULL;
    }

    ~A()
    {
        if(*fb)
            delete *fb;

        delete fb;
    }

    B** getfb()
    {
        return fb;
    }

private:
    B** fb;
};

class B:

class B
{
public:
    B()
    {
        B** fb = a->getfb();

        *fb = this;
    }

    ~B()
    {
        B** fb = a->getfb();

        delete *fb;            // <--- stack overflow

        *fb = NULL;
    }

private:
    A* a;
};

start() (a member function of class C):

void C::start()
{
    B** fb = a->getfb();        // 'a' is a pointer to an 'A' instance

    if(*fb == NULL)
        B* f = new B;
}

So, whenever I call start() and then call ~B(), I get a stack overflow!

Answer 1

Sounds right.

The type of fb is B** so the type of *fb is B*.

So when you say delete *fb you are calling the destructor for class B which is a recursive call that does not make progress toward a base case, hence the stack overflow.