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  2. RPG400-L
  3. April 2019

Re: [EXT] Re: Advice passing a large parameter

If this is an eternally described DS then Template is not needed.

Simply define the DS using the Extname and then in the PR/PI use LIKEDS. I might be inclined to use Qualified but that might have ramifications in the original program.

If you only want you procedure to change a single value then I would use CONST (so that som yahoo can't come along later and accidentally change a value) and have the char(20) turned by the procedure.

So if the DS is MyDS and the field is MyField then the call would look like:

MyField = ProcName( MyDS );

That way the fact that the field is changed is obvious. If you can add Qualified it is even more obvious. i.e.

My.DS.MyField = ProcName( MyDS );

Jon Paris

www.partner400.com
www.SystemiDeveloper.com

On Apr 12, 2019, at 11:13 AM, Greg Wilburn <gwilburn@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

So I'm confused...
The value that may or may not change (or return) is CHAR(20). Everything else would remain unchanged.

Should I use CONST or not?
Do I need to define the DS as TEMPLATE?

dcl-pi *n;
inPlist1 likeds(plist1);
end-pi;

dcl-ds plist1 extname('PLIST1DS') template;
end-ds;


-----Original Message-----
From: RPG400-L [mailto:rpg400-l-bounces@xxxxxxxxxxxxxxxxxx] On Behalf Of DeLong, Eric
Sent: Friday, April 12, 2019 11:02 AM
To: RPG programming on IBM i <rpg400-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: [EXT] Re: Advice passing a large parameter

I agree with David’s assessment. By default, RPG passes parameters by reference, meaning that a pointer is passed from the caller’s scope, so that the called program can access the callers storage directly.

The size and format of the address space is agreed upon by both parties. Since no data is actually being moved, the size of the parameter data is irrelevant to the performance question.

Passing by value is the expensive option you should try to avoid. This also includes large “return values” which are also passed by value. IBM gave us RTNPARM option to resolve that issue, but it’s not the default behavior, so just be aware.

Passing with CONST option performs well despite some small overhead with initialization of constant value storage in caller.

-Eric DeLong

On Apr 12, 2019, at 9:18 AM, David Gibbs via RPG400-L <rpg400-l@xxxxxxxxxxxxxxxxxx> wrote:

CAUTION: EXTERNAL EMAIL

**********************************************************************
On 4/12/2019 9:11 AM, Greg Wilburn wrote:
1. Just define the DS the same and pass it in (it could be
CONST)

I'm pretty sure this is the best way to do it. If you define the parm as const, I'm pretty sure it will be passed by reference, so there will be no additional storage allocated.

3. Define the PI as pointer and pass the address

No need to do this, as mentioned above, that's essentially what's already happening.

david



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