[C++知识库]SAP（九）的FiELD Symbol 和数据引用

字段符号可以看作仅是已经被解除引用的指针（类似于C语言中带有解引用操作符 * 的指针），但更像是C++中的引用类型（int i ;&ii= i;），即某个变量的别名，它与真真的指针还是有很大的区别的，在ABAP中引用变量则就是C语言中的指针。
添加链接描述

• 动态使用Assign语句

DATA : gv_1 TYPE c VALUE 'A',
      gv_2 TYPE c VALUE 'B',
      gv_3 TYPE c VALUE 'C',
      gv_4 TYPE c VALUE 'D',
      gv_5 TYPE c VALUE 'E'.
DATA : gv_name TYPE c LENGTH 10,
      gv_idx TYPE n.
FIELD-SYMBOLS : <fs>.

DO 5 TIMES  .
  CLEAR : gv_name.
  gv_name = 'GV_'.
  gv_idx = sy-index.
 CONCATENATE gv_name gv_idx INTO gv_name.
 ASSIGN (gv_name) TO <fs>.
 WRITE : <fs>.
 ENDDO.

• 结构体字段分配到Field Symbol

DATA : BEGIN OF gs_str,
   col1 TYPE char5 VALUE 'CHINA',
   col2 TYPE char10 VALUE 'BEIJING',
   col3 TYPE char15 VALUE 'TWIN BUILDING',
  END OF gs_str.

  FIELD-SYMBOLS : <fs1> LIKE gs_str,
                 <fs2> TYPE any.
  ASSIGN gs_str TO <fs1>.

  DO 3 TIMES.
    ASSIGN COMPONENT sy-index OF STRUCTURE <fs1> TO <fs2>.
    WRITE <fs2>.
 ENDDO.

Field Symbol语句与内表

TYPES : BEGIN OF t_line,
   col1 TYPE c ,
   col2 TYPE c,
  END OF t_line.


DATA : gs_wa TYPE t_line ,
      gt_itab TYPE HASHED TABLE OF t_line WITH UNIQUE KEY col1,
      gv_key(4) TYPE c VALUE 'col1'.
FIELD-SYMBOLS <fs> TYPE ANY TABLE.
ASSIGN gt_itab TO <fs>.
READ TABLE <fs> WITH TABLE KEY (gv_key) = 'X' INTO gs_wa.
WRITE : gs_wa-col1.

• 循环内表处理

DATA : BEGIN OF gs_line,
  carrid TYPE sflight-carrid,
  connid TYPE sflight-carrid,
  carrname TYPE scarr-carrname ,
  END OF gs_line.

  DATA gt_line LIKE TABLE OF gs_line.
  FIELD-SYMBOLS <fs> LIKE gs_line.

  SELECT carrid connid INTO CORRESPONDING FIELDS OF TABLE gt_line FROM sflight.

    LOOP AT gt_line ASSIGNING <fs>.
      SELECT SINGLE carrname INTO <fs>-carrname FROM scarr WHERE carrid = <fs>-carrid.
    ENDLOOP.

• TYPE REF TO 用来定义一个数据对象,这个数据对象是用来指向另外的数据的;
  *TYPE用来定义一个数据对象,它本身就是一个存储数据的对象,不是用来指向别的数据对象的.

• DATA: r1 TYPE REF TO c1.
  *属于ABAP面向对象编程，c1是一个类，r1定义了这个类的对象

• 数据引用

PARAMETERS : p_tname(30) DEFAULT 'SFLIGHT'.
DATA : dref TYPE REF TO data.
FIELD-SYMBOLS : <fs1> TYPE any,<fs2> TYPE any.
CREATE DATA dref TYPE (p_tname).
ASSIGN dref->* to <fs1>.
SELECT * FROM (p_tname) INTO <fs1> UP TO 3 ROWS.
  DO.
    ASSIGN COMPONENT sy-index OF STRUCTURE <fs1> TO <fs2>.
    IF sy-subrc NE 0.
      SKIP.
      EXIT.
    ENDIF.
    WRITE : <fs2>.
  ENDDO.
ENDSELECT.