是一个使用虚函数的类，对于一般的初学者有很大的帮助的哦。希望这个能对大家有一定的帮，当然你也可以用它修改一下变成多文件系统的。-The use of virtual function is a class for beginners in general of great help to the Oh. We hope that this can have some help, of course, you can also use it a chance to look into a multi-file system.