RE: Constants (was: *varsize array as procedure parameter)

And remember, 
If %addr(constParm) = *NULL
Only works in V5R1 and later. 
To get it to be *NULL, you have to pass in *OMIT (which is an entirely
different thread. <g>)


-Bob Cozzi
www.RPGxTools.com
RPG xTools - Enjoy programming again.


-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Scott Klement
Sent: Saturday, September 03, 2005 2:46 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: Constants (was: *varsize array as procedure parameter)

> If a const is just a pointer to a variable that isn't allowed to be
> changed ... is there any reason I couldn't take the address of that
> pointer, assign it to another (non-const) variable, and change the
> const's value that way?

The compiler won't let you take the address of a CONST variable and assign 
it to something.  (You can use it in a comparison, such as to check if 
it's *NULL, but when the parm is CONST, it won't let you store the output 
of %addr() into a variable.)

        // this code is legal:

              if %addr(ConstParm) = *NULL;

       // this code is not:

              ptr = %addr(ConstParm);

It is possible to TRICK the compiler, such as when you use a prototype 
that doesn't match the procedure interface, or when you go outside the 
scope of the subprocedure to get the address from the caller.  In those 
cases it is, in fact, possible to change the value of a CONST parameter.

But, that's going pretty far out of your way when you could've just left 
the "CONST" off of the prototype in the first place.