Distributed Systems Network Management (DSNM) Subsystem Interface Development Guide

_NULL
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109759—Distributed Systems Network Management (DSNM) Subsystem Interface
Development Guide
DSNM Library Services
_NULL
_NULL is an INT(32) literal, defining a null value for an extended memory pointer.
Always use _NULL for a null pointer value. Never test a pointer for null by comparing
it to _NULL; always use _ISNULL or _NOTNULL for such tests. The I process
program-development libraries use a range of null values. _NULL is guaranteed to be in
the range, but is not the only possible null pointer value.
A pointer set to _NULL causes an address trap, if used, to access memory.
Example
_LIST (list);
INT .EXT lm (list^member^def); !extended pointer to
!list member structure
@lm := _NULL;
WHILE _NOTNULL (@lm := _SUCCESSOR^LM (list,lm)) DO
BEGIN
...
END;
_NULL