STL：std::shared_ptr大致原理.-白红宇

STL：std::shared_ptr大致原理.

阅读量：6818 次

发布时间：2019-06-26

本文共 2581 字，大约阅读时间需要 8 分钟。

#include 
    
     #include 
     
      template
      
       class SharedPtr {public:    SharedPtr() = default;    explicit SharedPtr(Ty&& value);    explicit SharedPtr(const Ty& value);    ~SharedPtr();    SharedPtr(const SharedPtr
       
        & other);    SharedPtr(SharedPtr
        
         && other);    inline int use_count()noexcept    {        return *(this->counter);    }    //notice that:    //当对 SharedPtr进行 *(解引用操作)的时候会调用这个先把SharedPtr转为指针.    operator Ty*()noexcept;    SharedPtr
         
          & operator=(const SharedPtr
          
           & other); SharedPtr
           
            & operator=(SharedPtr
            
             && other);private: mutable int* counter{ nullptr }; //引用计数. Ty* data{ nullptr }; //存储数据的指针.};template
             
              SharedPtr
              
               ::SharedPtr(Ty&& value) :data{ new Ty{std::move(value)} }, counter{ new int{0} }{ ++(*(this->counter));}template
               
                SharedPtr
                
                 ::SharedPtr(const Ty& value) : data{ new Ty{value} }, counter{ new int{0} }{ ++(*(this->counter));}template
                 
                  SharedPtr
                  
                   ::SharedPtr(const SharedPtr
                   
                    & other) :counter{ other.counter }, data{ other.data }{ std::cout << "copy constructor" << std::endl; ++((*this->counter));}template
                    
                     SharedPtr
                     
                      ::SharedPtr(SharedPtr
                      
                       && other) :counter{ other.counter }, data{ std::move(other.data) }{ std::cout << "move-constructor" << std::endl; other.counter = nullptr; other.data = nullptr;}template
                       
                        SharedPtr
                        
                         & SharedPtr
                         
                          ::operator=(const SharedPtr
                          
                           & other){ std::cout << "copy operator=" << std::endl; if (*(this->counter) == 1) { delete this->data; delete this->counter; this->data = nullptr; this->counter = nullptr; }else{ --(*(this->counter)); } ++(*(other.counter)); this->counter = other.counter; this->data = other.data; return *this;}template
                           
                            SharedPtr
                            
                             & SharedPtr
                             
                              ::operator=(SharedPtr
                              
                               && other){ std::cout << "move operator=" << std::endl; this->counter = other.counter; this->data = std::move(other.data); other.counter = nullptr; other.data = nullptr; return *this;}template
                               
                                SharedPtr
                                
                                 ::operator Ty*()noexcept{ std::cout << "change to ptr" << std::endl; return (this->data);}template
                                 
                                  SharedPtr
                                  
                                   ::~SharedPtr(){ --(*(this->counter)); if (*(this->counter) == 0) { delete this->counter; delete this->data; this->data = nullptr; this->counter = nullptr; }}SharedPtr
                                   
                                     func(){ SharedPtr
                                    
                                      ptr1{ 10 }; SharedPtr
                                     
                                       ptr2 = ptr1; std::cout << ptr1.use_count() << "====" << ptr2.use_count() << std::endl; return ptr2;}int main(){// SharedPtr
                                      
                                        ptr{ 20 };// std::cout << *ptr << std::endl; //先调用了 operator Ty*();// std::cout << ptr.use_count() << std::endl; std::cout << func().use_count() << std::endl; return 0;}