Automatic variables are handled by the code produced by the compiler, which pushes and pops them from the stack as each procedure is called and exits. This is a "form" of allocation/deallocation, which is handled by the compiler/OS automaticly.
Dereferencing a pointer is asking for the value(s) that it points to. In RPG you can use %Str() or a variable Based() on a pointer.
Duane Christen
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Kurt Anderson
Sent: Friday, September 19, 2008 2:37 PM
To: RPG programming on the AS400 / iSeries
Subject: RE: Dynamic Array as return/output parameter in export
procedure
Ok so all (automatic, non-programmed) memory is allocated when a program
starts, even for "automatic" variables in procedures. So while
"automatic" variables initialize when the procedure starts, they simply
dereference the address when the procedure ends. Memory allocation
isn't a part of it at all.
Do I have that right?
Kurt Anderson
Application Developer
Highsmith
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Christen, Duane J.
Sent: Friday, September 19, 2008 1:53 PM
To: 'RPG programming on the AS400 / iSeries'
Subject: RE: Dynamic Array as return/output parameter in export
procedure
Until the activation group ends or the job ends all memory allocated
within the job stays allocated until it is specifically deallocated. If
your procedure allocates memory and does not deallocate it before the
procedure ends (normally or abnormally) and the address of the
allocation is not "saved"(1) then that memory can not be deallocated
until the activation group or job ends.
(1) A static variable to hold the address or the address is returned to
the caller.
Duane Christen
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Kurt Anderson
Sent: Friday, September 19, 2008 1:20 PM
To: RPG programming on the AS400 / iSeries
Subject: RE: Dynamic Array as return/output parameter in export
procedure
Scott,
"the fact that the pointer itself is released doesn't really matter.
the value of the pointer is preserved, and that's what counts."
My confusion had to do with what automatic cleanup was doing. I was
thinking it would cleanup the value at an address, not just release the
pointer. Does automatic cleanup ever clear out the value at the
address? My knowledge of the behind the scenes memory management is
basic at best.
I appreciate you bringing this to my attention.
Thanks,
Kurt Anderson
Application Developer
Highsmith
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Klement
Sent: Friday, September 19, 2008 10:12 AM
To: RPG programming on the AS400 / iSeries
Subject: Re: Dynamic Array as return/output parameter in export
procedure
Kurt Anderson wrote:
So myDynaArray_p is global? myDynaArray is local and not Static so it
would be cleaned up when the procedure ends. So the address of
myDynaArray_p would end up NULL right? Which would defeat the entire
purpose of the procedure.
myDynaArray is local -- but it's neither static nor automatic. It's
based on a pointer! RPG isn't going to manage it's storage for you!!
You have to manage it yourself.
so the labels "static" and "automatic" don't apply to based() data.
However, myDynaArray_p -- unless it's defined somewhere else that Lim
didn't show us -- is defined in automatic storage. So you're right that
the pointer itself will be reset to *NULL on subsequent calls. But, the
memory that it points to is not released -- just the pointer itself is.
Since the value that was in the pointer is passed back to the caller via
the piRtnListDynaArray parameter, the fact that the pointer itself is
released doesn't really matter. the value of the pointer is preserved,
and that's what counts.
It also doesn't matter that it's reset to *NULL, since the routine calls
%alloc() right away, anyway, which will provide a new address with new
storage.
So I guess I don't understand your concern, Kurt. What difference does
it make whether the pointer is in automatic or static storage?
If you got around that issue, I'd say that you'd also want to pass the
number of elements, otherwise the caller has no idea how many elements
there are to access and could attempt to access an elements beyond the
memory allocated.
On that score, I totally agree.
But would rather that he stop using this technique altogether :)
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