Modularization in ABAP: Macro,Subroutines & Function Modules

When you modularize source code, you place a sequence of ABAP statements in a module. Then, instead of placing all of the statements in your main program, you just call the module.When the program is generated, the source code in the modularization unit is treated as though it were actually physically present in the main program.

In this tutorial you will learn:

Need of Modularization
  • Improve the structure of the program.
  • Easy to read the code
  • Easy to maintain the code
  • Avoid redundancy and promotes code reuse
Various Modularization Techniques
  • Use of Macros
  • Use of include files
  • Subroutines
  • Function Modules
Lets look into each of them in detail :


If you want to reuse the same set of statements more than once in a program, you can include them in a macro.

You can only use a macro within the program in which it is defined, and it can only be called in lines of the program following its definition.

Macros  can be useful for long calculations or complex WRITE statements.


DEFINE <macro_name>

'Macro Statements

Macros can use Parameters &N where N = 1,2,3...


DATA: number1 TYPE I VALUE 1.

DEFINE increment.

ADD 1 to &1.



Increment number1.

WRITE number1.
Output: 2

Include Programs

Include Programs are solely for modularizing source code, and have no parameter interface. Include programs allow you to use the same source code in different programs. They  can be useful if you have lengthy data declarations that you want to use in different programs.


Include <include program Name>
Points to Note
  • Include programs cannot call themselves.
  • Include programs must contain complete statements.

WRITE: / 'User', SY-UNAME,/ 'Date', SY-DATUM.





Subroutines are procedures that you can define in any ABAP program and also call from any program. Subroutines are normally called internally, that is, they contain sections of code or algorithms that are used frequently locally. If you want a function to be reusable throughout the system, use a function module.


FORM <Subroutine> [<pass>].

<Statement block>.

<Subroutine> = Name of the subroutine

<pass> = Parameters being passed

Types of Subroutines

  1. Internal
    • Subroutine defined in same program being called.
    • Can access all the data objects declared in the main ABAP/4 program.
  2. External
    • Subroutine defined outside the program being called.
    • Need to use the <pass> option or declare data objects in common parts of memory.
Calling a Subroutine Internal Subroutines

PERFORM <subroutine> [<pass>]
<subroutine> = Name of the subroutine

<pass> = Parameters being passed

Data declared in main program is automatically available.

External Subroutines

PERFORM <subroutine>(<Program>) [<pass>].

PERFORM <subroutine> (<Program>) [<pass>] [IF FOUND].

PERFORM (<subroutine>) IN PROGRAM  (<Program>) [<pass>] [IF FOUND].

PERFORM <index> OF <subroutine1> <subroutine2> <subroutine3> [<pass>].
Points to Note
  • Nested calls are allowed in subroutines (i.e. PERFORM within a FORM ... ENDFORM ).
  • Recursive calls are also possible.
  • To define local data, use the DATA statement after FORM . Each time you enter the subroutine, the data is recreated (with an initial value) and released at the end (from the stack).
  • To define global data used within a subroutine, use the LOCAL statement after FORM . The values are saved when you enter the subroutine and then released at the end (from the stack)

Function Modules

Function Modules are general purpose ABAP/4 routines that anyone can use. Infact , there are a large number of standard function Modules available.

Function Modules are organized into Function Groups: Collections of logically related functions. A Function module always belongs to a Function Group.


FUNCTION <function module>


Important information Associated with Function Module

  • Administration
  • Import/Changing/Export parameters.
  • Table Parameters/Exceptions.
  • Documentation
  • Source code - L<fgrp>U01 . <fgrp> is the Function Group
  • Global Data - L<fgrp>TOP .Global data for the function group- Accessible across function modules in the function group.
  • Main Program - SAPL<fgrp> . Contains the list of all the include files for that function group
Call a Function Module

To call a function module, use the CALL FUNCTION statement:


[EXPORTING  f1 = a 1.... f n = a n]

[IMPORTING  f1 = a 1.... f n = a n]

[CHANGING   f1 = a 1.... f n = a n]

[TABLES     f1 = a 1.... f n = a n]

[EXCEPTIONS e1 = r 1.... e n = r n [ERROR_MESSAGE = r E]    

[OTHERS = ro]].

Function Groups

Function groups are containers for function modules. Infact, there are a large number of standard Function Groups. All of the function modules in a function group can access the global data of the group.

Like executable programs (type 1) and module pools (type M), function groups can contain screens, selection screens, and lists.

Points to Note

  • Function Groups cannot be executed.
  • The name of a function group can be up to 26 characters long.
  • When you create a function group or function module, the main program and include programs are generated automatically.
  • Function groups encapsulate data.
How to create a Function Group
  1. Goto Transaction SE80.
  2. Select Program in the DropDown.
  3. Write the name of the Function Group That you want to create. Generally User made Function groups start with "Z". e.g. - <Z_FUNCTION_GROUP_NAME> . Hit Enter Key.
  4. Note that The TOP Include is create by default if the user checks the option of creating a TOP include.
How to create a Function Module
  1. Create a function Group (say "ZCAL").
  2. Create a function module, set the attributes like  (Function group, Application, Short Text and Process Type) and Save.
  3. Include file "LZCALU01" will have source code of first function module.
  4. Include file "LZCALTOP" will have global data.
  5. Main program "SAPLZCAL" contains
    • Global data Include file "LZCALTOP"
    • Function modules include file "LZCALUXX"
    • User defined Include files "LZCALF..", "LZCALO.." and "LZCALI.."
  6. Define interface parameters and Exceptions
  7. Write the source code
  8. Activate Function Module
  9. Testing the Function Module - Single Test & Debugging
  10. Documenting and Releasing a Function Module
That's all to Modularity in ABAP.