CPP_SmartPtr_06.cpp

class Dog {
    shared_ptr<Dog> m_pFriend;//cyclic reference
    //weak_ptr<Dog> m_pFriend; //Solution to fix the problem
public:
    string m_name;
    Dog(string name) : m_name(name){cout << "Dog: " << m_name << " is defined!" << endl;}
    void bark() {cout << "Dog " << m_name << " rules!" << endl;}
    ~Dog() {cout << "Dog is destroyed: " << m_name << endl;};
    void makeFriend(shared_ptr<Dog> f){m_pFriend = f;}
};

int main(){
    shared_ptr<Dog> pD(new Dog("Gunner"));
    shared_ptr<Dog> pD1(new Dog("Smile"));
    pD->makeFriend(pD1);
    pD1->makeFriend(pD);
    //In this code, Dog destructor will not be called, when pD goes out of scope, 
    //pD1 still has a pointer points to pD; when pD1 goes out of scope, pD still 
    //has a pointer points to pD1
    //Will cause memory leak: cyclic reference!
    //using weak pointer to declare m_pFriend. 
    //Weak pointer has no ownership of the pointed object.
    return 0;
}