编写程序 read_fat12,读取 a.img 文件(该文件是 fat12 文件系统的软盘镜像)。要求：

• 通过分析 fat12 文件系统,打印出所有文件。

• 打印完成后,要求能够获取用户输入文件路径(以回车结束),程序查询 Fat12 文件,分别对目录文件、普通文件、不存在的文件进行做相应的输出-Programming read_fat12, read a.img file (which is a floppy disk image fat12 file system). Claim:

•　By analyzing the fat12 file system, print out all the files.

•　After printing is finished, requires the ability to get user input file path (with carriage return), program queries Fat12 file, directory files are ordinary files, that does not exist to do the appropriate output