Re: Another ILE question : CONST vs VALUE

Hi Bob -

On Mon, 7 May 2007 13:16:08 -0500, "Bob Cozzi" <bob@xxxxxxxxxxxx>
wrote:

CONST parms can't be changed by the called subprocedure, unless as Joe
explained
there is some subversion going on. But even then, if I recall correctly, there
is in fact a runtime error that will occur if you pull the address-of the const
and try to modify it. OS/400 pointers are very secure.

That's true only if the subprocedure is compiled with CONST on the PI.
If the subprocedure is compiled using a PR and PI without CONST, there
are no restrictions on changing the parameter because the compiler has
no way to know that the caller will be using a prototype with CONST.
Nor is there any run-time mechanism to detect the mis-match.

The stack thing is all academic--it doesn't really occur that way on real
computers like System i. Sure its simulated but at the end of the day, just a
pointer is passed by reference, not the value. Sure some things are put into
registers, but even VALUE parameters are passed by reference under the covers.
(Correctly if I'm wrong about this; if I am, I'm sure someone will.)

You're wrong about this. Parameters passed with VALUE have the actual
parameter placed in the call parameter list where a pointer would be
placed for a parameter passed by reference.

Ken
http://www.kensims.net/
Opinions expressed are my own and do not necessarily represent the views
of my employer or anyone in their right mind.