Clear Refresh Free区别

clear itab，仅清空HEADER LINE，对内表数据存储空间不影响，保留内存区。

clear itab[],清空内表数据存储空间里的内容。

refresh itab，不清空HEADER LINE，清除内表数据存储空间，但保存内存区。

free itab，不清空HEADER LINE，清空内表数据存储空间。

例子：

REPORT ZZZZZZZZZ.

types:begin of head, mantr(10) type c, id(10) type c, end of head. data gt_head type table of head with header line.

gt_head-mantr = 'wo'. gt_head-id = '00001'. append gt_head.

gt_head-mantr = 'you'. gt_head-id = '00002'. append gt_head.

free gt_head. write:gt_head.

loop at gt_head. write: / gt_head. endloop.

gt_head-mantr = 'he'. gt_head-id = '00003'. append gt_head. write:gt_head.