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Header line is the work area of the internal table. a internal with header line have a work area by default, and when you loop on the internal table with header line you don't need to mention work area data goes to header line.
like
LOOP AT ITAB.
*data goes to header line for each loop pass.
ENDLOOP.
Internal table without header line have no work area so you have to mention a work area when you are using them.
an internal table with header line would use a header or work area with the same name as the internal table for some processing to be done.
for example , you have an internal table in which you have 10 records.
YOu have to modify a value in 7th record.
read table itab index 7.
The above satement would get the 7th record into the header work area.
*From now onwards, you can use itab as just another structure which has one record in it with all the fields in the internal table(In this case the 7th record
If you uuse an internal table without header line, then you have to use a structure/explicit work Area to do the processing on particu;ar records.
like:
read itab into xtab index 7.
*Now xtab will have the 7th record.
In short,
an internal table with header = an internal table without header line + a work area which has the same structure as the internal table.
to process internal table data(records) you need some thing to store that record. for that purpose HEADER LINE appears.
if you read any entry from the internal table(either by using LOOP AT ITAB or READ TABLE ITAB) , the record will be fetched from the internal table body to the header line.
if you define an internal table with header line, the above record will be placed there.
if you create an internal table WITHOUT header,you should explicitly mention where to place the fetching record
If you have declared an internal table with header line , then any read statement or Loop statement made on the table writes the value into its header .
For Eg. IF you declare a table i_itab with header line
Then you can make a read/loop statement like
read table i_itab with key ....
or
Loop at i_tab where ...
Its not required to specify 'INTO work area'
The value will be there in its header , which you can get by accessing i_itab-*
Effectively a declaration of internal table with header line creates a table along with a work area of the same name.
An Internal table without header line have no work area. Thus we need to provide an explicit work area when we are using them.
LOOP AT itab INTO X_ITAB.
Now the data goes to the explicit work area x_itab
ENDLOOP.
Header line is the implicit work area of the internal table. An internal with header line have a work area by default, and when you loop on the internal table with header line you don't need to provide the work area data goes to header line.
LOOP AT ITAB.
*the data goes to header line(default workarea which has the same name itab) for each loop pass.
ENDLOOP.
Its always a better practise to use explicit workareas.
HEADER LINE is an implicit work area declaration, by which you can address the header line by the same name as your internal table.
Internal Table without header line are to addressed with a work area and you`ll have to address the work area by its name and not by the internal table name.
Bluesky
