文本文件读写

将students.txt中数据全部读入内存数组；

可选步骤：对格式不统一的数据进行格式化处理；

将学生按照姓名排序，并将结果保存到文件ordered.txt中；

将班级的学生全部选出，保存到文件classname.txt中。-Text file read and write data in all the students.txt read into memory array　Optional: on a unified data format is not formatted　to sort students by name, and save the results to a file ordered.txt in　the class All students elected to the file classname.txt in.