#include <iostream>
#include <memory>
using namespace std;class Parent;
typedef std::shared_ptr<Parent> ParentPtr;class Child
{
public:ParentPtr father;Child() {cout << "hello Child" << endl;}~Child() {cout << "bye Child\n";}
};typedef std::shared_ptr<Child> ChildPtr;class Parent {
public:ChildPtr son;Parent() {cout << "hello parent\n";}~Parent() {cout << "bye Parent\n";}
};void testParentAndChild()
{ParentPtr p(new Parent());ChildPtr c(new Child());p->son = c;c->father = p;
}int main()
{testParentAndChild();return 0;
}

#include <iostream>
#include <cassert>
#include <memory>
using namespace std;class Object
{
public:Object(int id) : m_id(id) {std::cout << "init obj " << m_id << std::endl;}    ~Object() {std::cout << "bye bye " << m_id << std::endl;}int id() const {return m_id;}
private:int m_id;
};void sharedPtrWithWeakPtr()
{typedef std::shared_ptr<Object> ObjectPtr;typedef weak_ptr<Object> WeakObjectPtr;ObjectPtr obj(new Object(1));// 一旦外部指向shared_ptr资源失效，那么weak_ptr管理的资源自动失效
    WeakObjectPtr weakObj2;           // 裸指针 WeakObjectPtr weakObj(obj);       // 指向shared_ptr指针
    WeakObjectPtr weakObj3(obj);   cout << "obj use count is " << obj.use_count() << endl;   // 1--尽管weak_ptr也指向obj，但他只是监听者，本身并不影响引用计数次数
    {// weak_ptr使用方法 // 外部至少还有一个shared_ptr来管理资源，同时p自己本身的资源 -- p.use_count >= 2 auto p = weakObj.lock();         // auto == ObjectPtrif (p) {cout << p.unique() << endl;  // 0 -- p.use_count() >= 2
        }else {}}// 不指向某份资源
//    obj.reset();
//    {
//        auto p = weakObj.lock();      // auto == ObjectPtr
//        if (p) {
//            assert(false);
//        }
//        else {
//            cout << "null" << endl;   // 如果调用reset，就会执行这句话
//        }
//    } // 此时, Object(1)已经失效 obj.reset(new Object(2)) ;{auto p = weakObj.lock();       // 返回值如果有效, 在外部必须有weakObj指向同一个资源 if (p) {assert(false);}else {cout << "null " << endl;   // null
        }}weakObj = obj;    // 又有效了 // 想知道weak_ptr有没有管理一份资源(外部有没有资源), 又不想生成一个shared_ptrif (weakObj.expired()) {// 资源过期了 -- true cout << "no ptr" << endl;}else {cout << "have resource\n";}
}int main()
{sharedPtrWithWeakPtr();return 0;}

#include <iostream>
#include <cassert>
#include <memory>
using namespace std;class Parent;
typedef std::shared_ptr<Parent> ParentPtr;
typedef std::weak_ptr<Parent> WeakParentPtr;class Child
{
public:WeakParentPtr father;                 // 只有一环换成 weak_ptr, 即可打破环
    Child() {cout << "hello Child" << endl;}~Child() {cout << "bye Child\n";}
};typedef std::shared_ptr<Child> ChildPtr;
typedef std::weak_ptr<Child> WeakChildPtr;class Parent {
public:ChildPtr son;                 Parent() {cout << "hello parent\n";}~Parent() {cout << "bye Parent\n";}
};void testParentAndChild()
{ParentPtr p(new Parent());ChildPtr c(new Child());p->son = c;            c->father = p;        cout << (c->father).use_count() << endl;cout << (p->son).use_count() << endl;
}int main()
{testParentAndChild();return 0;
}

handleChildAndParent(shared_from_this(), ps);

#include <iostream>
#include <cassert>
#include <memory>
using namespace std;class Parent;
typedef std::shared_ptr<Parent> ParentPtr;
typedef std::weak_ptr<Parent> WeakParentPtr;class Child : public std::enable_shared_from_this<Child>  // 奇异模板参数 CRTP
{
public:WeakParentPtr father;                 // 只有一环换成 weak_ptr, 即可打破环
    Child() {cout << "hello Child" << endl;}~Child() {cout << "bye Child\n";}void CheckRelation() {}
};typedef std::shared_ptr<Child> ChildPtr;
typedef std::weak_ptr<Child> WeakChildPtr;void handleChildAndParent(const ParentPtr& p, const ChildPtr& c);class Parent : public enable_shared_from_this<Parent> {
public:WeakChildPtr son;                 Parent() {cout << "hello parent\n";}~Parent() {cout << "bye Parent\n";}void CheckRelation() {auto ps = son.lock();if (ps) {//原理: 类中存在weak_ptr指针，通过一系列方式转换成 shared_ptr，然后传参 handleChildAndParent(shared_from_this(), ps);    // 使用CRTP来使用 本对象的指针 ★ ★ ★ ★
        }cout << "after call checkRelation\n";}
};void testParentAndChild()
{ParentPtr p(new Parent());ChildPtr c(new Child());p->son = c;            c->father = p;        cout << (c->father).use_count() << endl;cout << (p->son).use_count() << endl;p->CheckRelation();
}void handleChildAndParentRef(const Parent& p, const Child& c)
{auto cp = c.father.lock();auto pc = p.son.lock();if (cp.get() == &p && pc.get() == &c) {cout << "right relation" << endl;}else {cout << "oop !!!\n";}
}// const xxx&: 减少拷贝次数
void handleChildAndParent(const ParentPtr& p, const ChildPtr& c)
{auto cp = c->father.lock();auto pc = p->son.lock();if (cp == p && pc == c){cout << "right relation\n";}else {cout << "oop!!!\n";}
}int main()
{testParentAndChild();return 0;
}