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#include<iostream>
#include<string>
#include<memory>
using namespace std;
class Dog {
weak_ptr<Dog> m_pFriend;
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; }
void showFriend() {
//Compile error. m_pFriend cannot direct access the object like the normal pointer.
//cout << "My Friend is: " << m_pFriend->m_name << endl;
// The following code fix the problem. lock() function will create
//a shared_ptr of weak_ptr. It will check whether the weak pointer
//is still pointing to a valid object, and make sure that when the
// weak pointer is accessing the object, the object has not been
//deleted!
//If the weak pointer is empty, the lock() will throw an exception.
if (!m_pFriend.expired())
cout << "My Friend is: " << m_pFriend.lock()->m_name << endl;
cout << "He is owned by " << m_pFriend.use_count() << " pointers" << endl;
}
};
int main() {
shared_ptr<Dog> pD(new Dog("Gunner"));
shared_ptr<Dog> pD1(new Dog("Smile"));
pD->makeFriend(pD1);
pD1->makeFriend(pD);
pD->showFriend();
return 0;
}
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