With header line & with out header line ?

Question

what is difference between with header line & without header line ?

Answer 1

When you create an internal table object you can also declare a header line with the same name. You can use the header line as a work area when you process the internal table. The ABAP statements that you use with internal tables have short forms that you can use if your internal table has a header line. These statements automatically assume the header line as an implicit work area. The following table shows the statements that you must use for internal tables without a header line, and the equivalent statements that you can use for internal tables with a header line:
Operations without header line
Operations with header line
Operations for all Table Types
INSERT <wa> INTO TABLE <itab>.
INSERT TABLE ITAB.
COLLECT <wa> INTO <itab>.
COLLECT <itab>.
READ TABLE <itab> ... INTO <wa>.
READ TABLE <itab> ...
MODIFY TABLE <itab> FROM <wa> ...
MODIFY TABLE <itab> ...
MODIFY <itab> FROM <wa> ...WHERE ...
MODIFY <itab> ... WHERE ...
DELETE TABLE <itab> FROM <wa>.
DELETE TABLE <itab>.
LOOP AT ITAB INTO <wa> ...
LOOP AT ITAB ...
Operations for Index Tables
APPEND <wa> TO <itab>.
APPEND <itab>.
INSERT <wa> INTO <itab> ...
INSERT <itab> ...
MODIFY <itab> FROM <wa> ...
MODIFY <itab> ...
Using the header line as a work area means that you can use shorter statements; however, they are not necessarily easier to understand, since you cannot immediately recognize the origin and target of the assignment. Furthermore, the fact that the table and its header line have the same name can cause confusion in operations with entire internal tables. To avoid confusion, you should use internal tables with differently-named work areas.
The following example shows two programs with the same function. One uses a header line, the other does not.
With header line:
TYPES: BEGIN OF LINE,
COL1 TYPE I,
COL2 TYPE I,
END OF LINE.
DATA ITAB TYPE HASHED TABLE OF LINE WITH UNIQUE KEY COL1
WITH HEADER LINE.
DO 4 TIMES.
ITAB-COL1 = SY-INDEX.
ITAB-COL2 = SY-INDEX ** 2.
INSERT TABLE ITAB.
ENDDO.
ITAB-COL1 = 2.
READ TABLE ITAB FROM ITAB.
ITAB-COL2 = 100.
MODIFY TABLE ITAB.
ITAB-COL1 = 4.
DELETE TABLE ITAB.
LOOP AT ITAB.
WRITE: / ITAB-COL1, ITAB-COL2.
ENDLOOP.
Without header line:
TYPES: BEGIN OF LINE,
COL1 TYPE I,
COL2 TYPE I,
END OF LINE.
DATA: ITAB TYPE HASHED TABLE OF LINE WITH UNIQUE KEY COL1,
WA LIKE LINE OF ITAB.
DO 4 TIMES.
WA-COL1 = SY-INDEX.
WA-COL2 = SY-INDEX ** 2.
INSERT WA INTO TABLE ITAB.
ENDDO.
WA-COL1 = 2.
READ TABLE ITAB FROM WA INTO WA.
WA-COL2 = 100.
MODIFY TABLE ITAB FROM WA.
WA-COL1 = 4.
DELETE TABLE ITAB FROM WA.
LOOP AT ITAB INTO WA.
WRITE: / WA-COL1, WA-COL2.
ENDLOOP.
The list, in both cases, appears as follows:
1 1
2 100
3 9
The statements in the program that does not use a header line are easier to understand. As a further measure, you could have a further work area just to specify the key of the internal table, but to which no other values from the table are assigned.
Internal table with header line
you can use anywhere except obkect oriented concept.
Internal table without header line :
You should use in Object oriented concept..
Always try to use without header line,performance point of view it is best..
Example :
Without header line.
Structure
types : begin of ty_itab ,
matnr type mara-matnr,
end of ty_itab.
Internal table
data i_itab type standard table of ty_itab .
Work area
data wa_itab like line of i_itab
With header line
data : begin of i_itab occurs 0,
matnr like mara-matnr,
end of i_itab
itab with header lines are obsolete, anyway it will work but not recommended. instead use work area or more effiecient is field symbols. so donot use itab with header line.
i will explain use of itab w/o header line.
Data: itab1 type standard table of mara with header line occurs 0,
        itab2 type standard table of mara,
        wa_itab2 type mara.
loop at itab1.
"This will work fine.
endloop.
loop at itab2.
"This will give erro that itabd does not hav workarea
endloop.
"so write
loop at itab2 into wa_itab2.
"This will work
endloop.
<b>The difference between
whih header line and with out heater line of internal table.
ex:-
a) Data : itab like mara occurs 0 with header line.
b) Data: itab like mara occurs 0.
-While adding or retrieving records to / from internal table we have to keep the record temporarily.
-The area where this record is kept is called as work area for the internal table.
-The area must have the same structure as that of internal table. An internal table consists of a body and an optional header line.
-Header line is a implicit work area for the internal table. It depends on how the internal table is declared that the itab will have the header line or not.
a) Data : itab like mara occurs 0 with header line.
table is with header line
b) Data: itab like mara occurs 0.
table is without header line</b>
regards,
srinivas
<b>*reward for useful answers*</b>