我对继承变量有疑问。我的部分源代码:classPiston{//abstractclass...//virtualfunctions};classRectangularPiston:publicPiston{...//nonvirtualimplementationofthePistonfunctionsboolsetGridSize(...)//thisfunctiondoesn'texistsinthePistonclass{...}}classTransducer{//abstractclass...//virtualfunctionsprotected:Piston*m_pis