Static keyword and its application

1、 Used in this procedure page , Variables with the same name on different pages will not conflict ;
2、 Variable life cycle accompanies the whole program life cycle ;
1、 Static data members are also called class variables , Common data members are also called instance variables ; Static data members are each class All have one , The common data member is each instance There is one ;
2、 Static member functions ： Used to modify class Member function of
1. Static members can access each other , Including static member functions, accessing static data members and accessing static member functions .
2. Non static member functions can arbitrarily access static member functions and static data members .
3. Static member functions cannot access non static member functions and non static data members .
4. Call static member function , You can use member access operators （.） and （->） Calling static member functions for an object of a class or a pointer to an object of a class , You can also use the class name ：： Function name call （ Because he belongs to class , It's normal to call with a class name ）