基于point为基类的点—圆—圆柱体类的层次结构的改写，在程序中使用虚函数和抽象基类。类的层次结构的顶层是抽象基类Shape(形状)。Point(点), Circle(圆), Cylinder(圆柱体)都是Shape类的直接派生类和间接派生类。-Point for the base class based on points- round- cylinder class hierarchy rewritten, in a program using virtual functions and abstract base class. The top of the class hierarchy is the abstract base class Shape (shape). Point (point), Circle (circle), Cylinder (cylinder) are directly derived Shape class class and indirectly derived class.