ILE CL NULL Pointer Support Added at Release V6R1

Resolving The Problem

In V6R1, NULL pointer support in ILE CL was enhanced with the following additions:

1. Declaration of Pointer Variables

In V5R4 and before, the only way to ensure that a CL Pointer variable was set to NULL was to declare it without any initial value or address. As of V6R1, a pointer variable can be explicitly initialized to have an address of NULL using the ADDRESS parameter on the DCL statement.

Example

DCL VAR(&PTR1) TYPE(*PTR) ADDRESS(*NULL)


2. Changing Pointer Variables using CHGVAR

The special value *NULL can now be used in a CHGVAR statement to explicitly set a pointer to NULL.

CL Code Example

CHGVAR VAR(&PTR1) VALUE(*NULL)


3. Logic Statements

Pointer variables can now be compared against the special value *NULL in conditional statements.

CL Code Example

IF (&PTR1 *EQ *NULL) THEN(DO)

/* Code to execute here */

ENDDO


4. Compiling for TGTRLS(V5R4M0) and TGTRLS(V5R3M0)

Support for using *NULL in CHGVAR and in logic statements has also been extended to the TGTRLS(V5R4) and TGTRLS(V5R3) compilers. However,support for using ADDRESS(*NULL) in the DCL statement was not extended to the TGTRLS compilers.




Note: If the above is followed with an OPM CL program, the program will not compile and you will receive the following message:
CPD0711 30 Operands in expression not same type.

Support for *NULL was added in 6.1 and is valid in DCL statements for both OPM and ILE; however, it is only valid in pointer comparisons in ILE CL.

For OPM, the only way to compare a pointer CL variable to null is to compare it to a dummy CL pointer variable that is never used or declared with ADDRESS(*NULL). For example:

PGM                                                  
DCL        VAR(&NULLPTR) TYPE(*PTR) ADDRESS(*NULL)  
DCL        VAR(&P_DSPOPT) TYPE(*PTR) ADDRESS(*NULL)
:
IF         COND(&P_DSPOPT *EQ &NULLPTR) THEN(SNDMSG +  
    MSG('DSPOPT IS NULL') TOUSR(KPRYKE))            
IF         COND(&P_DSPOPT *NE &NULLPTR) THEN(SNDMSG +  
    MSG('DSPOPT IS NOT NULL') TOUSR(KPRYKE))        
ENDPGM