It is nothing but one type of Enhancement(user exit) like thing to write out code with respect to that program.
We use user exits in different ways from CMOD, SMOD etc
for certain programs, with in the program SAP has provided this type type of CUSTOMER FUNCTION '001'.
double click on the '001' and create your own include and write the related code in that for your requirement.
Customer Exit
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SAP creates customer exits for specific programs, screens, and menus within standard 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.
If you want to enhance the functionality of your SAP System, you should take advantage of the exits available in standard applications. There are two main reasons why you should use exits rather than modifying SAP software yourself. Add-ons attached to exits have the advantage that:
• They do not affect standard SAP source code
When you add new functionality to your SAP System using SAP’s exits, you do not alter the source code of standard SAP programs in any way. The code and screens you create are encapsulated as separate objects. These customer objects are linked to standard applications, but exist separately from SAP’s standard software package.
• They do not affect software updates
When you add new functionality to your SAP System using SAP’s exits, your objects (called customer objects) must adhere to strict naming conventions. When it comes time to upgrade a to a new software release, customer objects’ names ensure that they will not be affected by any changes or new additions to the standard software package.
Customer exits are not available for all programs and screens found in the SAP System. You can only use customer exits if they already exist in the SAP System. You can find more information about locating applications with pre-defined exits in Locating Applications that have Exits
CALL CUSTOMER-FUNCTION '003'
exporting
xvbak = vbak
xvbuk = vbuk
xkomk = tkomk
importing
lvf_subrc = lvf_subrc
tables
xvbfa = xvbfa
xvbap = xvbap
xvbup = xvbup.
Bluesky
