Incomplete Type Is Not Allowed

Question

Attempting to create as simple parent/child node class but running into Incomplete Type Is Not Allowed error. Why?

class Node {
public:
    Node ParentNode;  //Error on this line
    string NodeName;


    Node(Node *node) : ParentNode(*node) {

    }
};

Answer 1

You are trying:

Node ParentNode;  //Error on this line

but Node is not a complete type at this point (you are in fact defining it at this point), a structure cannot contain an instance of itself, it can contain a pointer or reference to an instance of itself but not an actual instance. After all, if such recursive containment were allowed, where would it end?

Answer 2

The error hints at the fact that the definition of a class is incomplete while the class is being defined.

An object can't contain an instance of its own type – it would be infinitely large.

You want

Node* ParentNode;

and

Node(Node *node) : ParentNode(node)