c++ - C++same class as member in class

Question

I have a class that should have a class of the same type as its member.

My declaration is the following:

class clsNode
{
private:
     clsNode m_Mother;
public:
     void setMother(const clsNode &uNode, int index);
};

C++ tells me "The object shows a type qualifier that is not compatible with the member function.

I don't know where I went wrong.

Answer 1

The reason is that the type of the member m_Mother has incomplete type at the point it is declared.

If you think about it. If it would have worked, you would create an object with an object inside with the same type, which in turn always have an object of the same type inside (and so on). The object would in a sense have infinite size.

One solution is to keep a pointer to the parent class instead.

class clsNode
{
private:
     clsNode* m_Mother;
public:
     void setMother(clsNode* uNode){ m_Mother=uNode; }
};

If you would like to have all parents always be alive during the lifetime of their children, you could use a shared pointer instead of a raw pointer.

class clsNode
{
private:
     std::shared_ptr<clsNode> m_Mother;
public:
     void setMother(std::shared_ptr<clsNode> uNode){ m_Mother=uNode; }
};

If you go with this solution you would originally create your objects with make_shared