Differences between public private protected

1. Access scope of the private, public, and protected methods.
* Private: It can only be accessed by methods in the class and cannot be accessed by objects in the class.
* Protected: it can be accessed by methods in the class and their friends functions, but cannot be accessed by objects in the class.
* Public: it can be accessed by methods in the class and their friends functions, or by objects in the class.

Second, method property changes after class inheritance:
* Use private inheritance. All methods of the parent class are changed to private in the subclass;
* Use protected to inherit. The protected and public methods of the parent class are changed to protected in the subclass, and the private method remains unchanged;
* Use public inheritance. The method attributes in the parent class are not changed;