【4】weak_ptr

//引入weak_ptr解决循环引用问题
#include <iostream>
#include <memory>
using namespace std;
class Test;
class Demo
{
public:
    weak_ptr<Test> t;   //指向Test类的弱智能指针
    Demo(){cout << "Demo的无参构造" << endl;}
    ~Demo(){cout << "Demo的析构" << endl;}
};

class Test
{
public:
    weak_ptr<Demo> d;  //指向Demo类的弱智能指针
    Test(){cout << "Test的无参构造" << endl;}
    ~Test(){cout << "Test的析构" << endl;}
};
int main()
{
    shared_ptr<Demo> p1(new Demo);
    shared_ptr<Test> p2(new Test);
    p1->t = p2;  //让p1中的指针成员指向p2
    p2->d = p1;  //让p2中的指针成员指向p1
    cout << "p1的计数:" << p1.use_count() << endl;
    cout << "p2的计数:" << p2.use_count() << endl;
    //weak_ptr<Demo> p3(new Demo);  weak_ptr不能独立使用，不能自己指向堆区的空间，需要使用shared_ptr赋值
    weak_ptr<Demo> p3(p1);
    cout << "p1的计数:" << p1.use_count() << endl;

    return 0;
}