RE: API- Userspace pointer Question

"cryptic" nah I just find them downright confusing... so you're not alone.

Ron Power
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"Holden Tommy" <Tommy.Holden@xxxxxxxxxxxxxxxxx> 
Sent by: rpg400-l-bounces@xxxxxxxxxxxx
2005/09/22 10:22 PM
Please respond to
RPG programming on the AS400 / iSeries <rpg400-l@xxxxxxxxxxxx>


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Subject
RE: API- Userspace pointer Question






Okay..I learned something today...

Honestly I didn't know that the entry size was what that field contained
in the generic header...(else I would be using it...)

I would never advocate bad programming.  I offered a solution to a
question which has served me so far.  I will be using the returned entry
size from now on (especially since I know it's there..)

That's just one of the "gotchas" of trying to learn APIs from IBM's
documentation..I find them cryptic (is it only me???)

Thanks for the lesson! 


Thanks,
Tommy Holden


-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Klement
Sent: Thursday, September 22, 2005 4:05 PM
To: RPG programming on the AS400 / iSeries
Subject: RE: API- Userspace pointer Question 

Tommy,

> s0300Ptr=s0300Ptr+%Size(SPLF0300)
>
> Where s0300Ptr is set to the original offset just add the %size of the

> DS returned.

The List APIs (including QUSLSPL) do not return the entries in fixed
positions of the user space. The documentation states that these
positions are variable -- and the API passes you a variable that
indicates the start of the data, how many entries there are, and how far
apart these entries are.

The emphasis in the above paragraph should be on "variable". While it's
true that IBM doesn't usually change these positions except when a
release changes, they'd be well within their rights to change them at
any time.

For example, perhaps the entries would be a different distance apart,
depending on the values of the input parameters. Or maybe the distance
between each entry would change, based on a PTF.

The problem with your code example is that you've got that distance
hardcoded in your program, and you're ignoring what the system tells
you.

I'm referring ot the following statement:

   s0300Ptr=s0300Ptr+%Size(SPLF0300)

%size() is a hard-coded value.  It's set at compile time, and won't ever
change no matter what you do.

It's not any more difficult to use a variable for the offset instead of
the size of your data structure!  Assuming that the entry size field is
in a variable called EntrySize you'd code:

   s0300Ptr=s0300Ptr+EntrySize

So my question is.... why do it wrong?  Even if you don't mind fixing it
with each release upgrade or PTF or whatever else breaks your code, how
is it saving you anything to type "%size(SPLF0300)" instead of
"EntrySize"?

So this is the rule of thumb:  When an API sends you an offset, size or
displacement, don't ignore it and hard-code the position.  Use the value
that the API sent you.
--
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