RE: Parameter prototype question

Here's an extract for the manual. There really should be more information than just the compiler MAY copy the parameter. As this can cause a run time error, this should be noted in the paragraph <Attention!>


When the keyword CONST is specified, the compiler may copy the parameter to a
temporary and pass the address of the temporary. Some conditions that would
cause this are: the passed parameter is an expression or the passed parameter has a
different format.

Attention!
Do not use this keyword on a prototype definition unless you are sure that
the parameter will not be changed by the called program or procedure.
If the called program or procedure is compiled using a procedure interface
with the same prototype, you do not have to worry about this, since the
compiler will check this for you.
Although a CONST parameter cannot be changed by statements within the
procedure, the value may be changed as a result of statements outside of the
procedure, or by directly referencing a global variable.

-----Message d'origine-----
De : rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] De la part de Mark S. Waterbury
Envoyé : samedi 15 mai 2010 03:36
À : RPG programming on the IBM i / System i
Objet : Re: Parameter prototype question

Hi, Barbara:

Given this whole set of problematic scenarios, would it
perhaps not be an improvement to have perhaps a new option on
the compile commands to allow the RPG IV compiler to at least
flag these situations with a WARNING message? Then, at least
the programmer could look at those warnings and perhaps take
preventive / corrective action accordingly.

Mark S. Waterbury

> On 5/14/2010 8:24 PM, Barbara Morris wrote:

Rory Hewitt wrote:

...
However, if you *don't* have CONST specified, you always

have to move

the value from the 10P 0 field into a 5P 0 work field to

pass it to

the procedure. Since that process (before you've even called the
procedure) will stop you from passing a value that's> 99999, then
the procedure call itself will never fail. ...

It's true that the procedure call won't fail, but you've

just shifted

the problem to the assignment statement where you set up

your 5P variable.

If the 10P variable has a value bigger than 99999, you will get an
exception no matter how you try to pass it to a 5P parameter. The
exception will happen either when you copy it to your own

5P variable

to satisfy the non-CONST parameter, or when the compiler

copies it to

its 5P temporary for the CONST parameter.

So you not only have to manually verify every CONST or VALUE
parameter, you also have to manually verify every

assignment. Or, to

put it another way, if for some reason you don't need to manually
verify every assignment, you shouldn't need to verify CONST

and VALUE parameters either.

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