C++自定义智能指针

template <class T>
class counted_ptr;// 智能指针引用计数类
template <class T>
class Ref_Ptr
{friend class counted_ptr<T>;
private:T* m_pTtr; // 实际的指针size_t counted_ptr; // 引用计数Ref_Ptr(T* p);virtual ~Ref_Ptr();
};template <class T>
Ref_Ptr<T>::Ref_Ptr(T* p)
{m_pTtr = p;counted_ptr = 1;cout<<"Ref_Ptr() 构造函数调用!"<<endl;
}template <class T>
Ref_Ptr<T>::~Ref_Ptr()
{if (m_pTtr){cout<<"~Ref_Ptr() 析构函数函数调用"<<endl;delete m_pTtr;counted_ptr = 0;}m_pTtr = NULL;
}// 智能指针对象
template <class T>
class counted_ptr
{
private:Ref_Ptr<T>* m_pRef; // 引用计数
public:counted_ptr();counted_ptr(T* p);~counted_ptr();// 重载运算=,将左对象引用计数-1,并判断是否delete;将右对象+1;counted_ptr<T> & operator = (counted_ptr& other);// 重载指针操作*,->T& operator *();T* operator ->();// 拷贝构造函数,引用计数+1counted_ptr(counted_ptr<T>& other);
};
template <class T>
counted_ptr<T>::counted_ptr()
{m_pRef = NULL;
}template<class T>
counted_ptr<T>::counted_ptr(T* p)
{m_pRef = new Ref_Ptr<T>(p);cout<<"counted_ptr(T* p) 构造函数调用"<<endl;
}template <class T>
counted_ptr<T>::counted_ptr(counted_ptr<T>& other)
{this->m_pRef = other.m_pRef;++(m_pRef->counted_ptr);cout<<"counted_ptr(& other) 拷贝构造函数被调用,当前引用计数"<< this->m_pRef->counted_ptr<<endl;
}template <class T>
counted_ptr<T>& counted_ptr<T>::operator=(counted_ptr& other)
{// 将右操作对象引用计数+1++(other.m_pRef->counted_ptr);// 由于左操作对象指向了新对象,需要将操作数-1;// 同时也防止了自赋值的方式.// 首先要判断这个对象是否已经指向了其他对象,这个很重要!防止左指针对象为null的情况.if (this->m_pRef){if (--(this->m_pRef->counted_ptr) == 0){delete this->m_pRef;}}this->m_pRef = other.m_pRef;cout<<"operator = 被调用,当前引用计数"<< this->m_pRef->counted_ptr<<endl;return *this;
}template <class T>
T& counted_ptr<T>::operator *()
{return *(m_pRef->m_pTtr);
}template <class T>
T* counted_ptr<T>::operator->()
{return (m_pRef->m_pTtr);
}template <class T>
counted_ptr<T>::~counted_ptr()
{cout<<"~counted_ptr() 析构函数被调用"<<endl;if ((--m_pRef->counted_ptr) == 0){cout<<"删除"<<endl;delete m_pRef;m_pRef = NULL;}if (m_pRef){cout<<"当前引用计数:"<< m_pRef->counted_ptr<<endl;}
}int  main()
{counted_ptr<int>* pPtr = NULL;{counted_ptr<int> g_ptr;{// 声明一个ptr1智能指针,并测试*运算符counted_ptr<int> ptr1(new int(4));counted_ptr<int> ptr2;cout<< "*ptr1="<< *ptr1<<endl;// 将生存期小的ptr1赋值给生存期更大的g_ptr;ptr2 = ptr1;system("pause");g_ptr = ptr1;system("pause");}// new int(4)并没有销毁,因为引用计数还有1个cout<<" *g_ptr="<<*g_ptr << endl;system("pause");}system("pause");getchar();return 0;
}

参考

std::shared_ptr - cppreference.com