说明：  这个程序是模拟采用二级目录结构的磁盘文件系统中的文件操作，它可以实现对文件的一些基本管理，如：读、写、删除文件等。通过这个程序可掌握文件子系统的原理，加深对二级目录结构的文件系统中用户管理、文件管理、目录管理的理解，并用程序实现对文件子系统的模拟。
(the procedure is simulated using two disk directory structure of the file system file manipulation, it can be achieved on some basic document management, such as : read, write, delete files. Through this procedure can grasp the principle document subsystems to enhance the structure of the two file system user management, document management, directory management, understanding, and the procedures to achieve the right documents subsystem simulation.)