Call function and call customer function

Question

Hi
Can anybody let me know what is the difference between CALL FUNCTION AND CALL CUSTOMER- FUNCTION .
i know call customer- function is used while we r working on user exits .
but is their any specific reason of difference ...
Thanks

Answer 1

CALL CUSTOMER-FUNCTION function_exit parameter_list.
Effect
This statement can be used in programs delivered by SAP. It includes the function module exit specified in function_exit . The function module exit is a customer exit. In an SAP program, it enables you to call a function module provided by SAP and implemented by the customer.
The indicator function_exit must be a three-digit text field literal. A function module exit is specified by SAP using the transaction SMOD and can be activated using the transaction CMOD in customer systems.
Specifications by SAP
An empty or partly implemented function module must be assigned to the function module exit using the transaction SMOD. The name of the function module consists of EXIT_, the program name, which contains the statement CALL CUSTOMER-FUNCTION, and the three-digit indicator in function_exit. The interface of the function module is completely defined by SAP.
Activation in the customer system
The transaction CMOD enables the customer to implement the source code of the function module within an enhancement project and to activate the function module exit. If the function module exit is not activated, the statement CALL CUSTOMER-FUNCTION is ignored. If the function module is activated, the corresponding function module is called in the same way as the general function module call.
Syntax and meaning of the parameter_list for the assignment of the actual parameters to formal parameters and for the exception handling are the same as in a general function module call. It is not possible to dynamically fill the interface.
CALL FUNCTION func
Syntax
CALL FUNCTION func { parameter_list
                   | parameter_tables }.
Effect
This statement calls the function module specified in func. The identifier func must be a character-type data object, which contains the name of a function module in uppercase letters during the statement execution. Each function module of an SAP system has a unique name, which is why you need not specify the function group.
Use additions parameter_list or parameter_tables (as of release 6.10) to statically or dynamically assign actual parameters to the formal parameters of the function module and return values to the non-class-based exceptions.
Note
If the name of a function module is specified by a constant or as a literal, the extended syntax check can check the statement.
Exceptions
Catchable Exceptions
CX_SY_DYN_CALL_ILLEGAL_FUNC
Cause: The called function is known but not active.
Runtime Error: CALL_FUNCTION_NOT_ACTIVE
Cause: The called function is unknown.
Runtime Error: CALL_FUNCTION_NOT_FOUND
CX_SY_DYN_CALL_ILLEGAL_TYPE
Cause: The type of the actual parameter does not fulfill the requirements of the function interface.
Runtime Error: CALL_FUNCTION_CONFLICT_GEN_TYP
Cause: The actual parameter does not have the length expected by the function.
Runtime Error: CALL_FUNCTION_CONFLICT_LENG
Cause: The actual parameter does not have the type expected by the function.
Runtime Error: CALL_FUNCTION_CONFLICT_TYPE
Cause: Only those functions can be called in the update task that are intended for it.
Runtime Error: CALL_FUNCTION_NO_VB
Cause: An actual parameter does not fulfill the alignment requirements of the respective formal parameter.
Runtime Error: CALL_FUNCTION_WRONG_ALIGNMENT
CX_SY_DYN_CALL_PARAM_MISSING
Cause: The function expects a parameter, which has not been passed by the caller.
Runtime Error: CALL_FUNCTION_PARM_MISSING
CX_SY_DYN_CALL_PARAM_NOT_FOUND
Cause: The caller has passed a parameter, which is not known to the function.
Runtime Error: CALL_FUNCTION_PARM_UNKNOWN
plz reward points if it helps