Re: Overlaying a DS Array In a LIKEREC DS

On 30-Jun-2010 19:13, Dennis Lovelady wrote:

<<SNIP>>

I would use Simon's suggestion with a (very) minor twist:

fafile uf e disk prefix('C.') usropn
:
d c ds likerec(rafile)
D @array S * Inz(%Addr(c))
d array ds likeds(ctlds) dim(20) based(@array)
:
Read afile c;

The two approaches are functionally equivalent, and which version
one prefers is merely a matter of taste.

FWiW: Although both an INZ(%ADDR(C)) in a declaration of the pointer and an assignment of the pointer to the %ADDR(C) during runtime have the same effect, there are valid reasons [which IMO are beyond simply one's personal taste] with regard to which method of setting the pointer is chosen. If the INZ is used, then the pointer is set in the first instruction of program processing, irrespective of any eventual use, so the cost of setting the pointer is always incurred during program start. While I concede setting just one pointer is insignificant, the possibility does exist to prevent unnecessarily setting the pointer if the array will not be referenced. Functionally however, choosing to not set the pointer until the data will be referenced ensures a "pointer not set" condition for misuse, thus exposing failed assumptions in the code. If the pointer is set since the first instruction, then any statement in the program is allowed to reference potentially uninitialized "data" in the array; i.e. to reference the data in the array even if no open has transpired, or even if no READ has populated the array. Thus if the file is never opened and\or never read, or even perhaps if no row was found, possibly the pointer need never have been set.

Regards, Chuck