主要在于引用计数的使用

代码示例:

template
    
     class Ptr{     template
     
           friend class Ptr;protected:    vint*                counter;    T*                    reference;    void Inc()    {        if(counter)        {            (*counter)++;        }    }    void Dec()    {        if(counter)        {            if(--(*counter)==0)            {                delete counter;                delete reference;                counter=0;                reference=0;            }        }    }    vint* Counter()const    {        return counter;    }    Ptr(vint* _counter, T* _reference)        :counter(_counter)        ,reference(_reference)    {        Inc();    }public:    Ptr()    {        counter=0;        reference=0;    }    Ptr(T* pointer)    {        if(pointer)        {            counter=new vint(1);            reference=pointer;        }        else        {            counter=0;            reference=0;        }    }    Ptr(const Ptr
      
       & pointer)    {        counter=pointer.counter;        reference=pointer.reference;        Inc();    }    template
       
            Ptr(const Ptr
        
         & pointer)    {        T* converted=pointer.Obj();        if(converted)        {            counter=pointer.Counter();            reference=converted;            Inc();        }        else        {            counter=0;            reference=0;        }    }    ~Ptr()    {        Dec();    }    template
         
           Ptr
          
            Cast()const { C* converted=dynamic_cast
           
            (reference); return Ptr
            
             ((converted?counter:0), converted); } Ptr
             
              & operator=(T* pointer) { Dec(); if(pointer) { counter=new vint(1); reference=pointer; } else { counter=0; reference=0; } return *this; } Ptr
              
               & operator=(const Ptr
               
                & pointer) { if(this!=&pointer) { Dec(); counter=pointer.counter; reference=pointer.reference; Inc(); } return *this; } template
                
                  Ptr
                 
                  & operator=(const Ptr
                  
                   & pointer) { T* converted=pointer.Obj(); Dec(); if(converted) { counter=pointer.Counter(); reference=converted; Inc(); } else { counter=0; reference=0; } return *this; } bool operator==(const T* pointer)const { return reference==pointer; } bool operator!=(const T* pointer)const { return reference!=pointer; } bool operator>(const T* pointer)const { return reference>pointer; } bool operator>=(const T* pointer)const { return reference>=pointer; } bool operator<(const T* pointer)const { return reference
                   
                    & pointer)const { return reference==pointer.reference; } bool operator!=(const Ptr
                    
                     & pointer)const { return reference!=pointer.reference; } bool operator>(const Ptr
                     
                      & pointer)const { return reference>pointer.reference; } bool operator>=(const Ptr
                      
                       & pointer)const { return reference>=pointer.reference; } bool operator<(const Ptr
                       
                        & pointer)const { return reference
                        
                         & pointer)const { return reference<=pointer.reference; } operator bool()const { return reference!=0; } T* Obj()const { return reference; } T* operator->()const { return reference; }};
                        
                       
                      
                     
                    
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     
    

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