Question

I’m creating a class named Circle and needs a public property to access its ‘parent’ Circle instance. Thus I code it like this:

class Circle {
public:
...
    Circle parent;
...
}

But this gave me an error: Incomplete type is not allowed

What should I do?

Answer 1

That cannot be done. Consider what the memory footprint of your type would be: a Circle contains a Circle, so it size cannot be smaller than the inner Circle, but that size is the same as the size of the outer Circle, reaching a contradiction.

Maybe you meant to store a pointer or smart pointer? That is allowed, since the size of the pointer is known by the compiler.