You can accomplish a "has-a" relationship with a forward declaration which basically tells "this class exists, it's just not declared yet"
#include <iostream>
using namespace std;
class Base
{
public:
Base() {}
};
// Forward declaration
class Derived1;
class Derived2 : public Base
{
friend class Derived1;
public:
Derived2() : Base() {}
private:
Derived1 *ptr;
};
class Derived1 : public Base
{
public:
Derived1(Derived2& obj) : Base(), ptr(&obj) {
obj.ptr = this;
}
private:
Derived2 *ptr;
};
int main() {
Derived2 obj2;
Derived1 obj1(obj2);
return 0;
}
This way the two classes can communicate with each other. Notice the private pointers and the initialization into the constructor. With the "friend" declaration one class is able to modify the other class's private members.