Re: Large Return values (was Re: Variable Length Field Question) -- RPG400-L

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Brad Stone wrote:

Don't you mean returning a pointer to a STATIC variable
local to the procedure, or a global variable in the
module? Returning a pointer to a local (automatic)
variable in a procedure may work for some cases. (Likely
the cases used for your unit tests.) But fail it will,
and the symptoms will be hard to debug.

Cheers! Hans

Is this because the storage is normally reclaimed after the
calling program ends?  Or does it reclaim it when it
"needs" the extra storage?  Or after the call to the
subprocedure that non-static storage is now available for
any other app to use?

It's because you're dealing with stack storage. At any time after the procedure returns, that area of storage is subject to reuse, typically by calls to other procedures, but also (depending on CPU and O/S) by random machine interrupts. Simply, you just can't trust anything on the popped side of the stack pointer on any hardware. (For me, it's a lesson I learned the hard way while writing a LISP interpreter in PDP-11 assembler language way back in 1978.)

Cheers! Hans

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