ABAP CONSTANTS: Syntax, Declaration and Usage Examples

The CONSTANTS statement is used to declare constants in ABAP. A constant is a named data object whose value is set at declaration and cannot be changed during the entire program runtime.

Using constants has several advantages:

1. Readability: Code becomes more understandable when self-explanatory names are used instead of “magic” values (e.g., numbers or single letters) (e.g., c_status_released instead of 'F').
2. Maintainability: When a fixed value changes (e.g., a threshold or tax rate), it only needs to be adjusted in one central place – in the CONSTANTS declaration – not at every place in the code where it’s used.
3. Safety: They protect against accidentally changing fixed values during program execution. Any attempt to assign a new value to a constant results in a syntax error.

Syntax

There are different ways to declare constants:

1. Declaration of a Single Constant

CONSTANTS <constant_name> TYPE <data_type> [LENGTH <length>] [DECIMALS <decimal_places>]
                           VALUE <value> | IS INITIAL.

• <constant_name>: The name that the constant should receive (must follow ABAP naming conventions).
• TYPE <data_type>: The ABAP data type (e.g., I, P, C, STRING, D, T, a Dictionary type like T001-BUTXT, or a self-defined type).
• LENGTH <length>: Optional length specification for types like C, N, X, P.
• DECIMALS <decimal_places>: Required for packed numbers (type P) to specify the number of decimal places.
• VALUE <value>: Mandatory (except with VALUE IS INITIAL). Here the fixed, immutable value is assigned. The value must match the data type. It can be a literal (e.g., 100, 'Hello', '19.99') or another, already defined constant.
• VALUE IS INITIAL: Assigns the type-specific initial value to the constant (e.g., 0 for I, space for C, empty string for STRING).

2. Declaration of Multiple Constants (Chain Statement)

CONSTANTS: <const1> TYPE <type1> VALUE <value1>,
           <const2> TYPE <type2> VALUE <value2>,
           ... .

With a colon after CONSTANTS, multiple constants can be declared separated by commas. The statement is terminated with a period.

3. Declaration of a Constant Structure

CONSTANTS: BEGIN OF <structure_name>,
             <component1> TYPE <type1> VALUE <value1>,
             <component2> TYPE <type2> VALUE <value2>,
             ...
           END OF <structure_name>.

This allows defining a structure whose components all have constant values. Access is then via <structure_name>-<componentN>.

Examples

1. Simple Constants

CONSTANTS c_max_length  TYPE i VALUE 255.
CONSTANTS c_app_name    TYPE string VALUE `My Super Report`.
CONSTANTS c_space       TYPE c LENGTH 1 VALUE ' '. " or VALUE IS INITIAL
CONSTANTS c_true        TYPE abap_bool VALUE abap_true. " Using ABAP boolean constants

2. Constant with Decimal Places (Type P)

CONSTANTS c_vat_standard TYPE p LENGTH 8 DECIMALS 2 VALUE '0.19'. " 19% VAT

3. Chain Statement for Multiple Constants

CONSTANTS: c_status_new        TYPE c LENGTH 1 VALUE 'N',
           c_status_in_progress TYPE c LENGTH 1 VALUE 'I',
           c_status_completed  TYPE c LENGTH 1 VALUE 'C',
           c_euro              TYPE waers VALUE 'EUR'.

4. Constant Structure

CONSTANTS: BEGIN OF c_colors,
             red   TYPE c LENGTH 1 VALUE '1',
             green TYPE c LENGTH 1 VALUE '2',
             blue  TYPE c LENGTH 1 VALUE '3',
           END OF c_colors.

5. Using Constants in Code

DATA gv_current_status TYPE c LENGTH 1.
DATA gv_text_length    TYPE i.
DATA gv_amount_net     TYPE p DECIMALS 2 VALUE '100.00'.
DATA gv_amount_gross   TYPE p DECIMALS 2.

gv_current_status = c_status_in_progress.
gv_text_length = strlen( c_app_name ).

IF gv_current_status = c_status_in_progress.
  WRITE: / 'The report runs under the name:', c_app_name.
  WRITE: / 'Maximum length is:', c_max_length.
  WRITE: / 'Color red has code:', c_colors-red.
ENDIF.

" Calculation with constant
gv_amount_gross = gv_amount_net * ( 1 + c_vat_standard ).
WRITE: / 'Gross amount:', gv_amount_gross CURRENCY c_euro.

" ****** SYNTAX ERROR ******
" The following code would result in a syntax error,
" as constants cannot be changed:
" c_max_length = 500.
" c_colors-red = 'X'.
" **************************

In summary: The CONSTANTS statement is an important tool in ABAP to make fixed values nameable, maintainable, and secure in code. They should always be used when a value is guaranteed not to change during program execution.