modern-cpp-tutorial/code/5/5.3.cpp

#include <iostream>
#include <memory>

class A;
class B;

class A {
public:
    std::shared_ptr<B> pointer;
    ~A() {
        std::cout << "A 被销毁" << std::endl;
    }
};
class B {
public:
    std::shared_ptr<A> pointer;
    ~B() {
        std::cout << "B 被销毁" << std::endl;
    }
};
int main() {
    std::shared_ptr<A> a = std::make_shared<A>();
    std::shared_ptr<B> b = std::make_shared<B>();
    a->pointer = b;
    b->pointer = a;
    
    return 0;
}