Explain about what is User Exits and Customer Exits?

In computer software, a user exit was a place in a software program where a customer can arrange for their own tailor-made Program to is called. In the R/3 system from SAP, a user exit was contrasted with a customer exit and allows a customer's developer to a Ccess program components and data objects within the R/3 system. In R/3, some user exits use include statements to include customer program enhancements that is called from the program. Other user exits use tables, that is accessed through customization.

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Difference between user exits & customer exits:

User Exit -A user exit is a three character code, instructs the system to access A program during system processing.

Sxx:s is-for-standard exits-is-delivered by SAP. XX represents the 2-digit exit number.

Uxx:u is for user exits this is defined by the user. XX represents the 2-digit exit number

Customer Exit -the R/3 enhancement concept allows to add your own functionality to SAP's standard business applications Withou t have to modify the original applications. SAP creates customer exits for specific programs, screens, and menus within standard R/3 applications. These exits do not contain any functionality. Instead, the customer exits act as hooks.     You can hang your own add-on functionality onto these hooks. *--Mani

The following document is on exits in SAP:-

The R/3 enhancement concept allows you to add your own functionality to SAP's standard business applications without havin G to modify the original applications.

SAP creates user exits for specific programs, screens, and menus within standard R/3 applications. These exits do not contain any functionality. Instead, the customer exits act as hooks. You can hang your own add-on functionality onto these hooks.

Types of Exits
There is several different types of user exits. Each of the these exits acts as hooks where can attach or "hang" your own add-ons.

Menu Exits
Menu exits add items to the Pulldown menus in standard SAP applications. You can use the these menu items to call up your own screens or to trigger entire add-on applications.

SAP creates menu exits by defining special menu items in the menu Painter. These special entries has function codes that begin with "+" (a plus sign). You specify the menu item's text when activating the item in an add-on project.

Screen Exits
Screen exits add fields to screens in R/3 applications. SAP creates screen exits by placing special subscreen areas on a standard R/3 screens and calling a customer subscreen from The standard screen ' s flow logic.

Function Module Exits
Function module exits add functions to R/3 applications. Function module exits play a role in both menu and screen exits.

When you add a new menu item to a standard pull down menu, you use a function module exit to define the actions that Shoul D take place once your menu is activated.

Function module exits also control the data flow between standard programs and screens exit fields. SAP application developers create function module exits by writing calls to customer functions into the source code of STA Ndard R/3 programs.

These calls has the following syntax:

Call Customer-function ' 001 '.

Field Exits
Field exits allow you to create your own programming logic for any data element in the Dictionary.  You can use the this logic to carry out checks, conversions, or business-related processing for any screen field. Example:the Data Element BBBNR identifies a company's international location number. You might want to set up your R/3 System so, all international location numbers is larger than 100.

The field exit concept lets you create a special function module, the contains this logic.

You assign the Special function module to the data element BBBNR. You then assign the "module to" programs and screens in which users can add new international location numbers. When you activate your field exit, the system automatically triggers your special routine whenever a user enters a company Location number.

You can use the "rsmodprf" program to create field exits.

An example of a user exits:-

MODULE user_exit_0001 INPUT
Case Okcode.
When the ' Back OR EXIT '.
Case Sy-dynnr.
When ' 100 '.
SET screen 0.
LEAVE screen.
When ' 200 '.
******************************************************************************
Note that the can write any code that satisfy your needs. ****
It is wrote as a sample code for reference sake. ****
And you can test it. ****
******************************************************************************
SET Screen 100.
LEAVE screen.
Endcase.
Endcase.

Explain about what is User Exits and Customer Exits?