4、　　掌握构造函数和析构函数的含义与作用、定义方式和实现，能够根据要求正确定义和重载构造函数。能够根据给定的要求定义类并实现类的成员函数；

掌握友元函数的含义，友元函数和成员函数的区别。

-4, master constructor and destructor of the meaning and effect, definition and implementation methods, to request the correct definition and overloaded constructor. Can be defined according to the requirements of a given class and implementation class member function　grasp the meaning of friend function, friend function and the difference between member functions.