说明：  对单个文件流进行操作，主要包括分割文件名 判断文件是否打开，判断文件的总大小，当前文件位置，当前行的长度，是否有下一行，读一行文件信息等等．
(Of a single file stream operation, including division of the file name to determine whether or not to open files to determine the total file size, the current file position, the current line length, whether it has the next line, reading his paper and so on.)