Question

I have two classes which depend on each other. I’ve solved this problem before but I can not for the life of me remember how to fix this. My simplified code is this:

struct MenuOption{
  string Text;
  int Choice;
  bool UseSubMenu;
  Menu SubMenu;
};

class Menu{
public:
  Menu(MenuOption optionlist[],int optioncount);
};

Answer 1

• Use forward declarations

I.e.:

// Forward declaration to assure A of B's existence.
class B;

class A { // uses B
  B* b;
};

class B { // uses A
  A* a;
};

• Use pointers and not object instances: because the compiler needs to know how much space to allocate to the members of a class. Having an object instance there is therefore not going to work because the compiler doesn’t know its size without seeing the full declaration of its class. Pointers, however, all have the same size which is known to the compiler without looking at anything extra.