智能指针的简单分析(一)

1. unique_ptr 一份数据只允许一个控制权

   struct StNode
   {
       int a;
       string str;
       StNode(int x = 0, string s = "") : a(x), str(s) {};
       ~StNode() {};
   };
   void Print_Unique_Ptr_B(std::unique_ptr<StNode> ptr)
   {
       cout << "Print_Unique_Ptr_B :" << "\n"
           << "a = " << ptr->a << "\n"
           << "str = " << ptr->str << endl;
   }
   void Print_Unique_Ptr_A(std::unique_ptr<StNode> ptr)
   {
       cout <<"Print_Unique_Ptr_A :" << "\n"
            << "a = " << ptr->a << "\n"
            << "str = " << ptr->str << endl;
       Print_Unique_Ptr_B(std::move(ptr));
   }
   void Use_UniquePtr()
   {
       std::unique_ptr<StNode> uptr(new StNode(10, "this"));// 一份数据只允许一个控制权
       Print_Unique_Ptr_A(std::move(uptr));
       if (!uptr)
       {
           cout << "uptr is nullptr" << endl;
       }
   }
   

2. shared_ptr 多个地方，共享同一份数据

   struct StNode
   {
       int a;
       string str;
       StNode(int x = 0, string s = "") : a(x), str(s) {};
       ~StNode() {};
   };
   void Print_Shared_Ptr_A(std::shared_ptr<StNode> ptr)
   {
       cout << "Print_Shared_Ptr_A :" << "\n"
           << "a = " << ptr->a << "\n"
           << "str = " << ptr->str << endl;
   }
   void Print_Shared_Ptr_B(std::shared_ptr<StNode> ptr)
   {
       cout << "Print_Shared_Ptr_B :" << "\n"
           << "a = " << ptr->a << "\n"
           << "str = " << ptr->str << endl;
   }
   void Use_SharedPtr()
   {
       std::shared_ptr<StNode> spTest = std::make_shared<StNode>(140, "SharedPtr");//多个地方，共享同一份数据
       Print_Shared_Ptr_A(spTest);
       Print_Shared_Ptr_B(spTest);
   }
   

   3、weak_ptr配合shared_ptr使用，解决A持有shared_ptr<B> pb,B持有shared_ptr<A> pa, 导致A、B资源不能释放的问题

   class CB;
   class CA
   {
   public:
       std::shared_ptr<CB> pb_;//调整为 std::weak_ptr<CB> pb_，看下效果
       ~CA()
       {
           cout << "A delete\n";
       }
   };
   class CB
   {
   public:
       shared_ptr<CA> pa_;
       ~CB()
       {
           cout << "B delete\n";
       }
   };
   void fun()
   {
       shared_ptr<CB> pb(new CB()); 
       shared_ptr<CA> pa(new CA());
       pb->pa_ = pa;
       pa->pb_ = pb;
       cout << pb.use_count() << endl;
       cout << pa.use_count() << endl;
   }
   

   https://www.cnblogs.com/TenosDoIt/p/3456704.html这篇文章讲的挺详细的，如果还有疑惑可以点击传送门。