确定文件中一行的长度。
LRECL= specifies the physical line length of the file. LINESIZE= tells the INPUT statement how much of the line to read.
DropOver以及不用此选项的默认执行的具体过程
By default, data that exceeds the current line length is written on a new line. When you specify DROPOVER, SAS drops (or ignores) an entire item when there is not enough space in the current line to write it. When an entire item is dropped, the column pointer remains positioned after the last value that is written in the current line. Thus, the PUT statement might write other items in the current output line if they fit in the space that remains or if the column pointer is repositioned.
9:Missover和TruncOver的区别
You need the TRUNCOVER option when you are reading data using column or formatted input and some data lines are shorter than others
missover和truncover的区别，对于一行结束时有缺省，如果是按列方式读取，(就是规定了列的数量)missover会把最后一个变量也置为缺失，而truncover会把缺失部分截除掉。
图上面的数据集是truncover的结果
建立标题、脚注以及取消
title1 'i am title1'; title2 'i am title2'; title3 'i am title3'; 建立三级标题
title;取消所有标题
footnote的用法和title的一样！