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