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ABAP Keyword Documentation →  ABAP - Reference →  Obsolete Language Elements →  Obsolete Declarations →  Internal Tables 

Internal Tables with Header Line

Outside classes, and if it is not a component of a structure or row in another internal table, it is still possible to create an internal table with a header line.

Other versions: 7.31 | 7.40 | 7.54

Declaration of Header Lines

Header lines of internal tables are created

  • by using the addition WITH HEADER LINE of the statement DATA to declare internal tables,

Properties of Header Lines

A header line is a work area whose

  • data type is the same as the row type of the internal table
  • whose name is the same as the name of the internal table.

If a header line exists, therefore, an ABAP program includes two data objects with the same name (the actual internal table and the header line). The internal table and header line are accessed as follows:

  • Many processing statements for internal tables have obsolete short forms in which the header lines is used as an implicit work area if no explicit work area is specified.
  • In all other cases, the statement and operand position decide whether the table body or the header line is used when the table name is specified. The header line is the usual choice. The name (and just the name) of an internal table with header line is interpreted as the table body only in the following cases:
  • In the statement FREE.
  • In the obsolete statement SEARCH.
  • When a token is specified dynamically in Open SQL (except when database tables are specified).

To force access to the table body in any operand position when a header line exists, square brackets can be specified directly after the name of an internal table (for example, itab[]).


Notes

  • A field symbol or a data reference can only address either the table body or the header line.

  • Both the table body and the header line are passed when a table with header line is passed to table parameters.

  • [] can be specified for internal tables without header line, but does not need to be. This is because the name (without []) of an internal table without header line is interpreted as the table body in all operand positions regardless.

  • In many operand positions that expect internal tables, the syntax check forces [] to be specified after the name of an internal table with header line.

Use

The use of header lines is highly error-prone, due to the repeated use of one name for two data objects. If at all possible, avoid creating and using header lines (even outside of classes).

  • Avoid using table parameters if at all possible.
  • In cases where a header line absolutely has to be created (such as in selection tables or in procedures that still require table parameters (generally only remote-enabled function modules)), never work with the header line and use the additional explicitly work areas declared explicitly instead.


Notes

  • A work area for replacing a header line can be declared very simply by using the addition LINE OF of the statements TYPES, DATA, and so on.

  • Do not mistake the use of an additional work area with the explicit completion of the implicit short forms, such as LOOP AT itab INTO itab. The latter case is one of the undesired ways to use a header line.

  • Tables with header lines do not offer any performance advantages.


Example

The following example shows a typical instance of handling internal tables with header lines: An internal table with header line (here the table parameter of a function module) is initialized using CLEAR, but the [] is not appended to the name. In this case, only the header line is deleted, which is not usually noticed until runtime.

FUNCTION work_with_tables.
*"---------------------------------
*"*"Local Interface
*"  TABLES
*"      table STRUCTURE  structure
*"----------------------------------

  CLEAR table.

  ...

ENDFUNCTION.