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

[Hans Boldt <boldt@xxxxxxxxxx>]

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