A Simple Realization of Reference Counting Technology and Smart Pointer
base object class
class Point
{
public:
Point(int xVal = 0, int yVal = 0) : x(xVal), y(yVal) { }
int getX() const
{
return x;
}
int getY() const
{
return y;
}
void setX(int xVal)
{
x = xVal;
}
void setY(int yVal)
{
y = yVal;
}
private:
int x, y;
};
Auxiliary class
//模板类作为友元时要先有声明
template <typename T>
class SmartPtr;
template <typename T>
class U_Ptr //辅助类
{
private:
//该类成员访问权限全部为private，因为不想让用户直接使用该类
friend class SmartPtr<T>; //定义智能指针类为友元，因为智能指针类需要直接操纵辅助类
//构造函数的参数为基础对象的指针
U_Ptr(T *ptr) : p(ptr), count(1) { }
//析构函数
~U_Ptr()
{
delete p;
}
//引用计数
int count;
//基础对象指针
T *p;
};
smart pointer class
template <typename T>
class SmartPtr //智能指针类
{
public:
SmartPtr(T *ptr) : rp(new U_Ptr<T>(ptr)) { } //构造函数
SmartPtr(const SmartPtr<T> &sp) : rp(sp.rp)
{
++rp->count; //复制构造函数
}
SmartPtr &operator=(const SmartPtr<T> &rhs) //重载赋值操作符
{
++rhs.rp->count; //首先将右操作数引用计数加1，
if (--rp->count == 0) //然后将引用计数减1，可以应对自赋值
delete rp;
rp = rhs.rp;
return *this;
}
T &operator *() //重载*操作符
{
return *(rp->p);
}
T *operator ->() //重载->操作符
{
return rp->p;
}
~SmartPtr() //析构函数
{
if (--rp->count == 0) //当引用计数减为0时，删除辅助类对象指针，从而删除基础对象
delete rp;
else
cout << "还有" << rp->count << "个指针指向基础对象" << endl;
}
private:
U_Ptr<T> *rp; //辅助类对象指针
};
use test
int main()
{
int *i = new int(2);
{
SmartPtr<int> ptr1(i);
{
SmartPtr<int> ptr2(ptr1);
{
SmartPtr<int> ptr3 = ptr2;
cout << *ptr1 << endl;
*ptr1 = 20;
cout << *ptr2 << endl;
}
}
}
system("pause");
return 0;
}
refer to:
- Simple implementation of C++ reference counting technology and smart pointers (the article is so well written, I will use it later)