解决循环引用问题

m0_60754876

于 2024-12-10 10:30:33 发布

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文章标签： c++ 开发语言

本文链接：https://blog.youkuaiyun.com/m0_60754876/article/details/144367163

版权

#include <memory>
     class B;
     class A {
     public:
         std::shared_ptr<B> ptr_to_b;
         A() { std::cout << "A constructor" << std::endl; }
         ~A() { std::cout << "A destructor" << std::endl; }
     };
     class B {
     public:
         std::shared_ptr<A> ptr_to_a;
         B() { std::cout << "B constructor" << std::endl; }
         ~B() { std::cout << "B destructor" << std::endl; }
     };
     int main() {
         std::shared_ptr<A> a = std::make_shared<A>();
         std::shared_ptr<B> b = std::make_shared<B>();
         a->ptr_to_b = b;
         b->ptr_to_a = a;
         // 这里a和b相互引用，引用计数都为2，离开作用域后无法正常销毁
         return 0;
     }

为啥离开作用域后无法正常销毁？

#include <memory>
     class B;
     class A {
     public:
         std::shared_ptr<B> ptr_to_b;
         A() { std::cout << "A constructor" << std::endl; }
         ~A() { std::cout << "A destructor" << std::endl; }
     };
     class B {
     public:
         std::weak_ptr<A> ptr_to_a;
         B() { std::cout << "B constructor" << std::endl; }
         ~B() { std::cout << "B destructor" << std::endl; }
     };
     int main() {
         std::shared_ptr<A> a = std::make_shared<A>();
         std::shared_ptr<B> b = std::make_shared<B>();
         a->ptr_to_b = b;
         b->ptr_to_a = a;
         // 现在不会出现循环引用问题，对象可以正常销毁
         return 0;
     }

这为啥就正常呢？