Smart Pointer C++

来源：Bloomberg Phone Interview

原帖：http://www.hawstein.com/posts/13.9.html

题目：
Write a smart pointer (smart_ptr) class.

代码：

 #include <iostream>  
 #include <cstdlib>  
 using namespace std;  
   
 template <typename T>  
 class SmartPointer{  
 public:  
   SmartPointer(T* ptr){  
     ref = ptr;  
     ref_count = (unsigned*)malloc(sizeof(unsigned));  
     *ref_count = 1;  
   }  
     
   SmartPointer(SmartPointer<T> &sptr){  
     ref = sptr.ref;  
     ref_count = sptr.ref_count;  
     ++*ref_count;  
   }  
     
   SmartPointer<T>& operator=(SmartPointer<T> &sptr){  
     if (this != &sptr) {  
       if (--*ref_count == 0){  
         clear();  
         cout<<"operator= clear"<<endl;  
       }  
         
       ref = sptr.ref;  
       ref_count = sptr.ref_count;  
       ++*ref_count;  
     }  
     return *this;  
   }  
     
   ~SmartPointer(){  
     if (--*ref_count == 0){  
       clear();  
       cout<<"destructor clear"<<endl;  
     }  
   }  
     
   T getValue() { return *ref; }  
     
 private:  
   void clear(){  
     delete ref;  
     free(ref_count);  
     ref = NULL; // 避免它成为迷途指针  
     ref_count = NULL;  
   }  
     
 protected:    
   T *ref;  
   unsigned *ref_count;  
 };  
   
 int main(){  
   int *ip1 = new int();  
   *ip1 = 11111;  
   int *ip2 = new int();  
   *ip2 = 22222;  
   SmartPointer<int> sp1(ip1), sp2(ip2);  
   SmartPointer<int> spa = sp1;  
   sp2 = spa; // 注释掉它将得到不同输出  
   return 0;  
 }