Re: Safe to maintain pointer to errno() ?

hi Dennis,

My specific question is whether it is safe to obtain a pointer to
errno only one time, and then reference the based value from then on.

When I asked IBM this question, I was told that the pointer probably won't change, it'll probably always point to the same area in memory. but they won't guarantee that this will always be the case, so they strongly recommend that you retrieve the pointer every time. (As ILE C programs do.)

Since the overhead of retrieving the pointer is insignificant, I just meekly complied.

It makes sense to me that errno's value would be at a static location
and won't float around in memory, but - again - I haven't seen any guarantee
of that.

In all of my tests and research, it is indeed a static location that never changes. The only problem is it's not guaranteed to _always_ be that way, going forward. So you risk compatibility breaking at some random time.

In C they do this:

extern int *__errno(void);
#define errno (*__errno())

So every time you reference errno in C, it does call the __errno() function, and the OS could potentially change the pointer. If it does, your C code will keep working...

So IMHO, RPG code should work the same way. It's easy enough to write subprocedures named geterrno() and seterrno() that retrieve the pointer, and then return/set errno appropriately.

So why fight it?