The NULL figurative constant represents a value used to indicate that data items defined with USAGE IS POINTER, USAGE IS PROCEDURE-POINTER, ADDRESS OF, or the ADDRESS OF special register do not contain a valid address. For example:
WORKING-STORAGE SECTION. 77 APTR USAGE POINTER VALUE NULL. PROCEDURE DIVISION. IF APTR = NULL THEN DISPLAY 'APTR IS NULL' END-IF.
In the above example, pointer APTR is set to NULL in the Working-Storage section. The comparison in the procedure division will be true and the display statement is executed.
On the AS/400 system, the initial value of a pointer data item or procedure-pointer data item with or without a VALUE clause of NULL, equals NULL.
(C) Copyright IBM Corporation 1992, 2005. All Rights Reserved.