Re: Procedure PR/PI question

Think you're a bit confused...

RPG passes pointers only unless you specify VALUE. Originally pointers
where all that were supported. CONST simply tells the compiler to prevent
the data being pointed to from being changed.

Here's another way to look at it
d somevar s 1000a

d myproc1
d parm1 1000a

d myproc2
d parm1 * value

myproc1(samevar);
myproc2(%addr(somevar));

What's passed for myproc1 and myproc2 is EXACTLY the same, the address of
somevar.

In fact, you could use either prototype for the same called
procedure/program.

Charles






On Wed, May 1, 2013 at 7:14 AM, whatt sson <whattssonn@xxxxxxxxx> wrote:

Joep, thats what i meant.

Some other
The keywords "value" and "const" are a bit confusing. In C (RPG these

days

seems to be a bit of a strange mix of C and Pascal syntax and semantics)
all parameters are passed simply by value. The keyword "const" means that
you can not change it within the called function (of course you can still
change it through other references). If you have complex data (not just
simple datatypes) you can pass a pointer (which is passed by value like

all

other datatypes). In C it's more common to work with pointers. This is
simple, elegant and predictable. You have only one way of passing
parameter, namely "by value". If you don't want to copy lots of data on

the

stack you simply use &var (%addr(var) in RPG).

So i think i'm going to use "value" always (not with local procs only).

And

if i need to pass lots of data (in principle always if i want to pass

more

than just a basic type) i pass a pointer. The latter can be done with

%addr

in the caller or by definining the parameter as "const". However if i use
"const" the behavior is not consistent. The compiler decides whether to
copy the variable or not (and i never want a copy just the const). This

way

the semantics are the same as in C (except for the use of const), which
comes in handy if i ever want to convert the code to C. I don't see a

real

downside in this approach, except that it makes more use of pointers with
which many RPG'ers are not comfortable. And that the semantics of "const"
is not the same as in C. So i'm still in doubt whether to use const (if i
want to pass a pointer) or use "value" with %addr. The latter case is a

bit

convoluted but we're used to that in RPG (need at least 6 specs to start

a

free form procedure impl without even one parameter). But i can't use the
const semantics of keyword "const" (like in C) because it mostly also

means

"copy".




On Wed, May 1, 2013 at 1:39 AM, Sam_L <lennon_s_j@xxxxxxxxxxx> wrote:

Correct, but if you inadvertently forget to define a local variable on

a

d-spec and a global one exists the procedure will quietly and quite
happily use the global one, possibly with disastrous or random effects.

Sam


On 4/30/2013 6:39 AM, paultherrien@xxxxxxxxxxxxxxxxxx wrote:

I may not understand what you are saying, but it is my understanding

that if

you use a d-spec in your procedure to define a variable then the

variable is

local to the procedure.


Paul


-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:

rpg400-l-bounces@xxxxxxxxxxxx]

On Behalf Of Sam_L
Sent: Monday, April 29, 2013 5:31 PM
To: RPG programming on the IBM i (AS/400 and iSeries)
Subject: Re: Procedure PR/PI question

I would like to have an option that says "All the variables I define

in

this procedure are local unless I specify otherwise". I know, if I

put

it in a separate source file I get the same effect, but this isn't

always

practical or politically acceptable in some shops.

Sam

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