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+1 counted_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
