First, Scott has a point, several infact. But to your questions here.
The caller does not know how many elements are needed but it will need to know how many elements are used if it has to do any processing of the array. The caller will also have to know how many elements are used from previous calls so there must be some kind of counter/index to keep track of the elements used. You also have to keep track of the storage used so you don't try to use storage you have not allocated.
The %realloc isn't a trick, a dynamic array (or any allocated storage) is, partly, an attempt to use storage sparingly/wisely. %Realloc takes the storage currently pointed at by the pointer parameter and extends/contracts the storage allocated to that pointer to the size parameter. %Realloc may need to find a larger area of unreserved storage to fit the request, so it will copy the contents of the currently allocated storage to the new block, this will change the value of the pointer.
If you look at the structure arrayDs there is a field called "static" that has nothing to do with the RPG keyword static. I use the field "static" in the structure to describe the un-changing portion of the structure, the storage that is initially allocated to store the "count" of elements and "size" of allocated storage, both fields overlay the "static" field.
Duane Christen
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Lim Hock-Chai
Sent: Friday, September 19, 2008 10:05 AM
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: Dynamic Array as return/output parameter in export
procedure
In my case, the caller does not really know how many elem is needed.
The called procedure (export procedure) determines that. From your
example, are you saying that the %realloc would trick the system to
think that the heap storage belongs to the caller? Or am I over
thinking?
Note: The export procedure could get called multiple times before the
caller dealloc the dyna array. Making the array static in the export
procedure might not work for me.
From
"Christen, Duane J." <Duane.Christen@xxxxxxxxxxxxx> wrote in message
news:<mailman.11963.1221835629.2545.rpg400-l@xxxxxxxxxxxx>...
This is the way I would do it.
Build your structure like this:
D arrayDs DS based(pointer)
D Qualified
D static
D count 10I 0 Overlay(static)
D size 10I 0 Overlay(static : *NEXT)
D array 20A Dim(32767)
Use a template in a copybook if possable, because both the caller and
called procedure need the definition.
Then, in the caller allocate the storage needed for the static part of
the structure:
pointer = %Alloc(%Size(arrayDs.Static));
Call the procedure, making sure that the pointer is passed by reference.
In the called procedure, when you need more storage for your array do:
arrayDs.Size += %Size(arrayDs.Array * 200);
arrayDs.Count += 200;
piRtnListDynaArray = %ReAlloc(arrayDs.Size);
When you are done loading your array set the arrayDs.Count value to the
last element in the array that was loaded, so that the caller knows how
many elements of the array were loaded.
Duane Christen
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Lim Hock-Chai
Sent: Friday, September 19, 2008 9:14 AM
To: RPG programming on the AS400 / iSeries
Subject: Dynamic Array as return/output parameter in export procedure
is there a way to safely return a dynamic array from an export procedure
to the caller? Something like below just doesn't look very safe for me.
P getListInDynaArray...
D pi
D piKey 4
D piRtnListDynaArray...
D *
D myDynaArray s 20 dim(32767) based(myDynaArray_p)
/free
myDynaAry_p = %alloc(200);
. . .
piRtnListDynaArray = myDynaArray_p
/end-free
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