Re: CONST and VALUE revisited

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 29/01/2009, at 7:05 AM, Douglas Handy wrote:

> Note that a service program is the same as an internal subprocedure  
> in this
> regard.  It is a prototyped call to an external program (not  
> *SRVPGM) which
> I believe will not enforce the CONST checking.

It will as long as the called program also specifies CONST.

CONST in a prototype used by the caller has no real effect. It's  
documentation only although it does allow the compiler to use  
temporary variables to handle type conversions. However in the callee  
(i.e., the one with both a PR and a PI) the compiler will do its best  
to enforce the "CONSTness" (yuck) of the variable.

Problems only arise when, say, someone modifies the caller and thinks  
"I'll prototype that external call" and specifies CONST on all the  
supposedly input-only parameters but does not modify the callee to  
honour the same behaviour. In this case the callee does not know it  
should not change the parameter variable (and no information was  
provided to the compiler so it did not verify) so a change in the  
callee will be visible in the caller (as long as the compiler did not  
generate a temporary in the caller).

Regards,
Simon Coulter.
--------------------------------------------------------------------
   FlyByNight Software         OS/400, i5/OS Technical Specialists

   http://www.flybynight.com.au/
   Phone: +61 2 6657 8251   Mobile: +61 0411 091 400        /"\
   Fax:   +61 2 6657 8251                                   \ /
                                                             X
                 ASCII Ribbon campaign against HTML E-Mail  / \
--------------------------------------------------------------------