C++引用计数智能指针

#include <iostream>
using namespace std;

template<typename Type>//引用计数的智能指针
class auto_ptr_
{
public:
    auto_ptr_(Type *t = NULL):ptr(t), count(1)
    {
    }
    auto_ptr_(const auto_ptr_<Type>& at) :ptr(at.ptr), count(at.count+1)
    {}
    auto_ptr_<Type>& operator=(const auto_ptr_<Type> &at)
    {
        if (this != &at)
        {
            if (ptr != NULL)
            {

                if (count == 1)
                    this->~auto_ptr_();//如果ptr已经存在且唯一指向目标。
                ptr = at.ptr;
                count = at.count + 1;
            }
        }
        return *this;
    }
    ~auto_ptr_()
    {
        if (count == 1)
        {
            if (ptr != NULL)
            {
                delete ptr;
                ptr = NULL;
            }
        }
    }
    Type* operator->()
    {
        return ptr;
    }
    Type& operator*()
    {
        return *this;
    }
private:
    Type *ptr;
    int count;
};
int main()
{
    int *a = new int(3);
    int *b = new int(4);
    auto_ptr_<int> ps(a);
    auto_ptr_<int> pb(ps);
    auto_ptr_<int> pc(b);
    pc=pb;
    auto_ptr_<int> pd(pc);
    return 0;
}