RE: Calling an RPG procedure with optional parameters from C code

*OMIT doesn't make a parameter "optional".

*OMIT means you can pass the special value of *OMIT.

*NOPASS == optional.  You can chose to pass something or not 
pass anything.

I think you are splitting hairs here, especially as in my original post I
said I was using *OMIT

When you pass *OMIT to an RPG IV procedure, what you are really 
doing is passing a NULL pointer.

I am not sure that is true.  In the called procedure you test the 
field's address for NULL, not its value.

It is indeed true.  In RPG you test if %addr(someParm) = *NULL;

My apologies, I read "passing a NULL pointer" as "passing a NULL value"

Not sure I understand what you are saying.  The RPG prototype 
specified an int or the C prototype?

Both! That was the problem.  The RPG correctly had INT and the C one
incorrectly also had INT.  When I changed the C one to be a pointer to INT I
could use a NULL in the C code.


regards

Stephen Osborn
Financial Messaging & Integration
Misys Banking Systems
+44 (0)20 8486 1790
stephen.osborn@xxxxxxxxx
 

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx 
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Wilt, Charles
Sent: 01 November 2006 17:45
To: RPG programming on the AS400 / iSeries
Subject: RE: Calling an RPG procedure with optional 
parameters from C code

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Osborn, Stephen
Sent: Wednesday, November 01, 2006 11:35 AM
To: RPG programming on the AS400 / iSeries
Subject: RE: Calling an RPG procedure with optional 

parameters from C 

code

RPG doesn't allow optional parameters to be specified before 
required ones either.

That is true for *NOPASS but not for *OMIT

*OMIT doesn't make a parameter "optional".

*OMIT means you can pass the special value of *OMIT.

*NOPASS == optional.  You can chose to pass something or not 
pass anything.

When you pass *OMIT to an RPG IV procedure, what you are really 
doing is passing a NULL pointer.

I am not sure that is true.  In the called procedure you test the 
field's address for NULL, not its value.

It is indeed true.  In RPG you test if %addr(someParm) = *NULL;

Since you are dealing with parameters passed by reference, 
you are asking if the pointer passed in is NULL.

Note that *OMIT only works with parameters passes by 
reference.  You can't use it for parameters passed by VALUE 
whereas you can use *NOPASS for parameters passed by 
reference or by value.

Thus, in your C/C++ program just make sure you pass a 

NULL pointer 

for the *OMITted parameter.

I tried that, before I asked a question here, and it didn't 

work.  The 

procedure prototype said that an INT is being passed as the first 
parameter and when I specified a NULL there the module would not 
compile.

Not sure I understand what you are saying.  The RPG prototype 
specified an int or the C prototype?

However I just changed the first parameter of the procedure 

prototype 

to be pointer to INT and now NULL is acceptable and it is 

now working.

As RPG, by default, uses pass by reference, in a C 

procedure prototype 

the declarations should be of type 'pointer to xxx'.  All the other 
fields in my C procedure prototype were 'pointer to xxx' so 

that one 

was probably just a typo.

This makes sense and is what I was saying.

If your RPG proto looks like
D myproc     pr
D  parm1               10i 0   options(*OMIT)
D  parm2               10i 0   options(*OMIT)
D  parm3               10i 0 

Or

D myproc     pr
D  parm1               10i 0   
D  parm2               10i 0 
D  parm3               10i 0  

Then in either case, your C prototype should look like 
(please excuse any typos, been 10+ years since I wrote any C)

void MYPROC (int *parm1, int *parm2, int *parm3)
 
C will allow you to pass a NULL point for any of the 3 parameters.

HTH,

Charles Wilt
--
iSeries Systems Administrator / Developer Mitsubishi Electric 
Automotive America
ph: 513-573-4343
fax: 513-398-1121