Overview of Function Modules (SAP Library

Overview of Function Modules

Function modules are ABAP routines that are stored in a central function library. They are not application-specific, and available systemwide. The ABAP Workbench comes with a large number of standard function modules.

Like form routines, function modules encapsulate program code, and provide an interface for data exchange.

However, there are significant differences between function modules and form routines:

Function modules must belong to a pool called a function group.
They possess a fixed interface for data exchange. This makes it easier for you to pass input and output parameters to and from the function module.
For example, you can assign default values to the input parameters. The interface also supports exception handling. This allows you to catch errors and pass them back to the calling program for handling.
They use their own memory area. The calling program and the function module cannot exchange data using a shared memory area - they must use the function module interface. This avoids unpleasant side effects such as accidentally overwriting data.
You call a function module by its name (which must be unique) in a CALL FUNCTION statement.

The Function Builder allows you to develop, test, and document new function modules. You can also use it to display information about existing function modules:

Administration	Specifies information like the development class a function belongs to, the person responsible for the module, a short description of the module.
Import	Contains a list of the formal parameters that are used to pass data to a function module. For further information, refer to Displaying Information about Interface Parameters
Export	Contains a list of the formal parameters that are used to receive data from a function module. For further information, refer to Displaying Information about Interface Parameters
Changing	Contains a list of the formal parameters that are used both to pass data to and receive data from a function module. For further information, refer to Displaying Information about Interface Parameters
Tables	Specifies the tables that are to be passed to a function module. Table parameters are always passed by reference. For further information, refer to Displaying Information about Interface Parameters
Exceptions	Shows how the function module reacts to exceptions. For further information, refer to Displaying Information about Interface Parameters
Documentation	Provides information about the interface and exceptions
Source code	Program code of the function module
Global data	The global data used by the function module.
Main program	Program code of the main program.

Function modules play an important role in the modularization of applications. You can use them to encapsulate a particular function or group of related functions.

Modularization allows you to avoid redundancy. It also makes your programs easier to read and understand.
Modularized programs are easier to maintain and keep up-to-date.

The modularization principle:

Function Groups

The Function Builder administers function modules that logically belong together in function groups. Function groups are containers for function modules. They can also contain global data declarations and subroutines that are available to all of the function modules in the group.

The following illustration shows the organization of function modules within a function group:

This graphic is explained in the accompanying text

For each function group <fgrp> there is a main program, generated by the system, called SAPL<fgrp>.
The main program contains INCLUDE statements for the following programs:

L<fgrp>TOP. This contains the global data for the function group.
L<fgrp>UXX. These includes contain the function modules themselves. The numbering XX indicates the chronological order in which the function modules were created. This includes L<fgrp>U01 and L<fgrp>U02 contain the first two function modules in the function group.

L<fgrp>F01, L<fgrp>F02... These includes can be used to write subroutines (forms) that can be called as internal forms by all function modules in the group.

Displaying a Function Group

To display a function group, choose Goto ® Function groups ® Display group. A dialog box appears in which you can enter the name of the function group.