abap describe的用法（程序示例）

describe 用来输出变量（field structure table）的有关属性
主要有以下3种用法：
Field Properties 

1. DESCRIBE FIELD ... 

Properties of an Internal Table 

2. DESCRIBE TABLE ... 

Distance Between Two Fields 

3. DESCRIBE DISTANCE ... 以下程序演示了相关用法：
 REPORT demo_describe_field.

TYPES: surname(20)  TYPE c,
       street(30)   TYPE c,
       zip_code(10) TYPE n,
       city(30)     TYPE c,
       phone(20)    TYPE n,
       date         TYPE sy-datum.

TYPES: BEGIN OF address,
         name TYPE surname,
         code TYPE zip_code,
         town TYPE city,
         str  TYPE street,
       END OF address.

TYPES: BEGIN OF phone_list,
         adr TYPE address,
         tel TYPE phone,
       END OF phone_list.

TABLES spfli.

DATA: BEGIN OF test,
  col1(3) TYPE c,
  col2(2) TYPE c,
  col3 TYPE i,
END OF test,
dist TYPE i.

DATA: text(8) TYPE c VALUE 'abcdefgh', len TYPE i,
      numtext(10) TYPE n VALUE '0123456789', typ(1) TYPE c,
      pl TYPE phone_list,
      n TYPE i,
      float TYPE f, out TYPE i,
      pack TYPE p DECIMALS 2, dec(1) TYPE c.


DESCRIBE FIELD text LENGTH len IN CHARACTER MODE.
WRITE: text, 'has length', len.

DESCRIBE FIELD numtext TYPE typ.
WRITE: / 'Numerical text has type', typ.
DESCRIBE FIELD spfli-fltime TYPE typ.
WRITE: 'and SPFLI-FLTIME has type', typ.

DESCRIBE FIELD float LENGTH len IN BYTE MODE OUTPUT-LENGTH out.
WRITE: / 'Floating point number has length', len,
                        'and output length', out.

DESCRIBE FIELD pack DECIMALS dec.
WRITE: / pack, 'has', dec, 'Decimals'.

DESCRIBE FIELD pl TYPE typ COMPONENTS n.
WRITE: / 'The complex field PL has type', typ, 'with', n, 'components'.

DESCRIBE DISTANCE BETWEEN test-col3 AND test-col1 INTO dist
         IN BYTE MODE.
WRITE: / 'The distance between TEST-COL3 and TEST-COL1 is', dist.