#include <iostream> using namespace std; template<class T> class SmartPtr { public:     SmartPtr(T *p){         try         {             use_count = new int(1);         }         catch (...)         {             delete ptr;             ptr = nullptr;             use_count = nullptr;             cout << "Allocate memory for use_count fails." << endl;             exit(1);         }         cout << "Constructor is called!" << endl;     }     ~SmartPtr(){         // 只在最后一个对象引用ptr时才释放内存         if (--(*use_count) == 0)         {             delete ptr;             delete use_count;             ptr = nullptr;             use_count = nullptr;             cout << "Destructor is called!" << endl;         }     }     SmartPtr(const SmartPtr<T> &orig){         // 浅拷贝         ptr = orig.ptr;         use_count = orig.use_count;         ++(*use_count);         cout << "Copy constructor is called!" << endl;     }     SmartPtr<T>& operator=(const SmartPtr<T> &rhs){         // 浅拷贝         ++(*rhs.use_count);         // 将左操作数对象的使用计数减1，若该对象的使用计数减至0，则删除该对象         if (--(*use_count) == 0)         {             delete ptr;             delete use_count;             cout << "Left side object is deleted!" << endl;         }         ptr = rhs.ptr;         use_count = rhs.use_count;         cout << "Assignment operator overloaded is called!" << endl;         return *this;     } private:     T *ptr;     // 将use_count声明成指针是为了方便对其的递增或递减操作     int *use_count; }; int main() {     // Test Constructor and Assignment Operator Overloaded     SmartPtr<int> p1(new int(0));     p1 = p1;     // Test Copy Constructor     SmartPtr<int> p2(p1);     // Test Assignment Operator Overloaded     SmartPtr<int> p3(new int(1));     p3 = p1;     cin.get();     return 0; }