Optional Parameters and CL Procedures

Hey, Ted:

In "Adding New Parameters to RPG Programs," you stated that CL programs require that the exact number of expected parameters be passed to them. That's not entirely true.

If you use ILE CL (source type CLLE), you do not have to pass in the same number of parameters as expected. You can use the same technique you described in the RPG example. You would assign the parameter to the work field with CHGVAR, but monitor the assignment for message MCH3601 ("pointer not set for location referenced"). If that message is sent, you assign the default value to the work field.

PGM        PARM(&OPTION_P &COPIES_P)

DCL        VAR(&OPTION_P) TYPE(*CHAR) LEN(1)
DCL        VAR(&COPIES_P) TYPE(*DEC) LEN(1)

DCL        VAR(&OPTION) TYPE(*CHAR) LEN(1)
DCL        VAR(&COPIES) TYPE(*DEC) LEN(1)

CHGVAR     VAR(&OPTION) VALUE(&OPTION_P)
MONMSG     MSGID(MCH3601) +
             EXEC(CHGVAR VAR(&OPTION) VALUE(A))
CHGVAR     VAR(&COPIES) VALUE(&COPIES_P)
MONMSG     MSGID(MCH3601) +
             EXEC(CHGVAR VAR(&COPIES) VALUE(1))

Thanks for listening.

--Doug

Thanks for writing, Doug. And thanks to the other readers who corrected me as well. My comment applied only to OPM CL, which I am currently using. I haven't done a formal study, but it seems that many iSeries shops use RPG IV along with OPM CL. One comment I've heard several times is that OPM supports the Retrieve CL Source (RTVCLSRC) command but ILE CL doesn't. All I can say is that I have probably retrieved CL source code from a program object less than half a dozen times since 1988, when I first touched a System/38. Given a choice between being able to retrieve source code from the program object and being able to pass fewer than the number of defined parameters, I'd much rather have the latter ability. This seems to me an excellent reason to dump OPM CL, as many have dumped RPG III (A.K.A. RPG/400).

Monitoring for MCH3601 has another purpose. You will need to monitor for MCH3601 if you write your own RTV-type commands. IBM's RTV commands, such as Retrieve Job Attributes (RTVJOBA) and Retrieve User Profile (RTVUSRPRF), can return a lot of different data, but require you to code only the parameters that interest you. If you write a CL program that processes an RTV-type command, you'll need to monitor for MCH3601 for optional parameters.

 PGM        PARM(&OPTION &TEXT)

 DCL        VAR(&OPTION) TYPE(*CHAR) LEN(1)
 DCL        VAR(&TEXT) TYPE(*CHAR) LEN(50)

 CHGVAR     VAR(&OPTION) VALUE(whatever...)
 MONMSG     MSGID(MCH3601)

 CHGVAR     VAR(&TEXT) VALUE(whatever...)
 MONMSG     MSGID(MCH3601)

--Ted