Re: ILE bug or "feature"?

[bmorris@xxxxxxxxxx]

>Date: Wed, 7 Feb 2001 00:48:19 -0600 (CST)
>From: Scott Klement <klemscot@klements.com>
>
>To be honest with you, this surprised me as well.   He really should be
>getting "pointer not set for location referenced" or similar message when
>XTEST2 is first called.
>
>It seems to me that the addresses of the parameters should be *NULL if
>they weren't ever SET by passing parms to the procedure.  The fact that
>they happened to point to the same area of memory that the previous
>procedure pointed to seems like an extraordinary coincidence!
>
>This implies that when the module is loaded into memory that it's not
>initializing its variables to NULL, as I believe that it should.
>
>I'd be interested in what Barbara & Hans have to say.

Scott, when parameters are passed by reference, the procedure receives a
pointer to the actual parameter.  If the compiler were to initialize
that pointer to null, no parameters could ever be received.

By default, ILE procedures have no idea how many parameters were passed.
To get that information, an operational descriptor has to be passed (not
an OPDESC one, just a minimal one giving the number of parms).  RPG and
CL always pass this minimal operational descriptor (RPG had to, to support
*PARMS), but C and COBOL only do it if the programmer requests it.  RPG
only uses it to provide the value of %parms though.  RPG doesn't copy
the parameters to some other storage.  It gives you direct access to the
parameters as they were passed.

Mark, when I tried this with a CALL, I indeed got a "pointer or
parameter error".  That's what I expected, because with a CALL, the
number of parameters is always available; for a CALL, RPG has to copy
the parameter pointers to its own storage anyway (I forget why), and
it only copies the parameters that were actually passed, and sets the
other local parameter pointers to null.

Regarding bug or feature, I don't think it's either.  I think it would
be great if the ILE environment could provide something that I don't
think is available anywhere else, namely runtime checking of parameters.
But the system works the way it works.  The existence of %parms and
*PARMS implies that the system won't prevent you from accessing
parameters that are not passed; the fact that failure to check %parms
sometimes causes a nice pointer-not-set error doesn't mean that problems
from not checking %parms are limited to that error.

Barbara Morris


+---
| This is the Midrange System Mailing List!
| To submit a new message, send your mail to MIDRANGE-L@midrange.com.
| To subscribe to this list send email to MIDRANGE-L-SUB@midrange.com.
| To unsubscribe from this list send email to MIDRANGE-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---