FORM is a keyword used in SAP ABAP programming.
This tutorial covers its introduction & syntax details.
FORM
Basic
form
FORM form.
Additions
1. … TABLES itab1 …
itabn
2. … USING p1 … pn
3. … CHANGING p1 …
pn
Effect
Defines a subroutine called by
PERFORM
Example
PERFORM WELCOME.
FORM WELCOME.
WRITE /
‘Hello world’.
ENDFORM.
The subroutine WELCOME called by the
PERFORM statement outputs ‘Hello world’
Notes
Subroutines defined by
FORM can have parameters and local fields. These parameters and local fields
shadow global fields. Any local fields you declare with DATA after a FORM
statement are recreated and initialized for each PERFORM call. When the call has
finished, the memory for local fields is released again. FORM statements are not
allowed within FORM … ENDFORM structures (i.e. no nested definitions). Nested
and recursive calls are possible. The optional parameters must always be
specified in the order TABLES , USING and CHANGING .
Addition 1
…
TABLES itab1 … itabn
Effect
TABLES allows you to pass internal
tables with or without header lines to subroutines. For information about
assigning types TABLES parameters, see Type assignment . TABLES parameters are
passed by reference.
Example
DATA: BEGIN OF X.
INCLUDE
STRUCTURE SFLIGHT.
DATA: ADDITION(8) TYPE C,
END OF X.
…
PERFORM U
USING X.
…
FORM U USING X STRUCTURE SFLIGHT.
WRITE:
X-FLDATE.
ENDFORM.
Example
TYPES: BEGIN OF
FLIGHT_STRUC,
FLCARRID LIKE SFLIGHT-CARRID,
PRICE LIKE
SFLIGHT-FLDATE,
END OF FLIGHT_STRUC.
DATA: MY_FLIGHT TYPE FLIGHT_STRUC
OCCURS 0 WITH HEADER LINE,
IBOOK1 LIKE SBOOK OCCURS 0 WITH HEADER
LINE,
IBOOK2 LIKE IBOOK1 OCCURS 0,
STRUC LIKE SBOOK.
PERFORM
DISPLAY TABLES MY_FLIGHT IBOOK1 IBOOK2 USING STRUC.
FORM DISPLAY TABLES
P_ITAB LIKE MY_FLIGHT[]
P_BOOK1 LIKE IBOOK1[]
P_BOOK2 LIKE
IBOOK2[]
USING P_STRU LIKE STRUC.
DATA L_CARRID LIKE
P_ITAB-FLCARRID.
…
WRITE: / P_STRU-CARRID, P_STRU-CONNID.
…
LOOP
AT P_ITAB WHERE FLCARRID =
L_CARRID.
…
ENDLOOP.
…
ENDFORM.
Addition 2
…
USING p1 … pn
Effect
Defines the formal parameters p1 ,… pn which
are replaced by actual parameters when you call the subroutine.
The formal
parameters p1 ,… pn can have a particular type (see Type assignment ). You can
also specify the transfer type (i.e. how you want to pass
them).
Note
Transfer types: USING … p …
Transfer is by
reference. This means you can change the transferred field continually in the
subroutine.
USING … VALUE(p) …
When you specify VALUE(…) ,
transfer is by value, i.e. the field contents are passed to the relevant local
field. VALUES parameters thus behave in the same way as local
fields.
Addition 3
… CHANGING p1 … pn
Effect
The
parameters after CHANGING can accept the same specifications as those after
USING .
To link the VALUE specification with the change of a parameter value,
you can use the addition CHANGING … . Then, all the formal parameters
specified by VALUE(…) are transported back to the actual parameters at the end
of the subroutine (i.e. after ENDFORM ). If the subroutine is terminated by a
dialog message, none of the parameters referenced by CHANGING VALUE …
changes.
Otherwise, the effect of USING and CHANGING is
identical.
Example
DATA: NUMBER_1 TYPE I VALUE 1,
NUMBER_2 TYPE
I VALUE 2,
TEXT_1(10) VALUE ‘one’,
TEXT_2(10) VALUE ‘two’.
PERFORM
CONFUSE USING NUMBER_1
NUMBER_2
TEXT_1
NUMBER_1
TEXT_2.
FORM
CONFUSE USING PAR_NUMBER_1 TYPE I
PAR_NUMBER_2 TYPE I
PAR_TEXT_1 TYPE
C
VALUE(PAR_V_NUMBER_1) TYPE I
VALUE(PAR_V_TEXT_2) TYPE C.
ADD 3 TO
PAR_V_NUMBER_1.
ADD 4 TO PAR_NUMBER_1.
ADD NUMBER_1 TO
PAR_NUMBER_2.
TEXT_2 = ‘three’.
PAR_TEXT_1 = PAR_V_TEXT_2.
PAR_V_TEXT_2
= ‘four’.
ENDFORM.
Field contents after the PERFORM
call:
NUMBER_1 = 5
NUMBER_2 = 7
TEXT_1 = ‘two’
TEXT_2 =
‘three’
Note
In subroutines, you are recommended to use the following
procedure:
Pass input parameters as USING parameters and output parameters as
CHANGING parameters. If in doubt, pass the parameter by VALUE . You should be
particularly careful with passed SY fields. For performance reasons, data
objects which contain tables should not be passed by VALUE if at all possible.
You can protect TABLES parameters whose heasder lines must remain unchanged with
LOCAL . STATICS allows you to create global fields with a local visibility area.
In the case of local fields which are initialized on each call, you can replace
DATA by STATICS . With frequently called FORM routines, this can lead to a
noticeable improvement in performance. To avoid shadowing problems with
parameters, you are recommended to keep to the naming convnetion for fields in
subroutines. You should, for instance, always start FORM parameters with the
prefix ‘P_’ and local fields with the prefix ‘L_’ .