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Re: incorrect return code on vms...

From: David H. Thornley
Subject: Re: incorrect return code on vms...
Date: Fri, 01 Dec 2000 11:05:46 -0600

Donald Sharp wrote:
> On Fri, Dec 01, 2000 at 09:47:52AM -0600, David H. Thornley wrote:
> >
> >
> > Donald Sharp wrote:
> > >
> > > If the return codes for a program are reversed on vms,
> > > such that success = 1 and failure = 0, then cvs would
> > > always exit with a failure on vms systems.  Attached
> > > is a patch to fix this problem.
> > >
> > Assuming that VMS has a conforming C compiler, this is not
> > a problem.  The C system interprets both 0 and EXIT_SUCCESS
> > as successful exits, and EXIT_FAILURE as a failure exit.
> > These are defined in <stdlib.h>.
> You missunderstand what I did.  This has nothing to do
> with the c compiler.  It has everything to do with what
> cvs returned as a exit code.  The vms system( according to
> the ChangeLog ) interprets return codes from programs as follows:
> 0 - Program failed
> 1 - Program Succeeded.
No, it has to do with what happens between the writing of the
C program and the status return to the operating system.  That
is where the C compiler comes in.

In Unix, for example, the null pointer value is all-bits-zero,
zero is a successful program exit code, and other values are
various sorts of errors.  Following this, in C, 0 (cast to
pointer type) is a null pointer value, and 0 is an exit code
that represents success.

On some platforms, all-bits-zero is a valid pointer, and there
is some other invalid pointer.  This does not break working
code, as the C system simply translates (void *)0 (or whatever)
to the appropriate pointer value.

Similarly, on some platforms, 0 is the failure exit, and the
C system simply translates appropriately.

> Original code did this:
>         exit( err ? EXIT_FAILURE : 0 );
> Within cvs err is set to 0 for program success and >0 for failure.
In other words, the program is completely correct here.  That is
perfectly good code according to the standard.

> stdlib.h on vms should set EXIT_FAILURE to 0.  Therefore the
> above exit() code will always return 0 on vms.  I assumed that EXIT_SUCCESS
> would be set to the correct thing.  Hence:
If stdlib.h on vms sets EXIT_FAILURE to 0, it is not a conforming
C compiler, and, as I said, you should find a better one or
gripe to your vendor if you run into this problem.  0 is, by
definition in the Standard, a successful value.  If the exit()
function has something like "return !exit_value" in it, it will
pass the correct value to the operating system.  (This is
platform-specific code, of course, which the standard libraries
pretty much have to be.)

EXIT_SUCCESS may be set to 0, or it may be set to some other
value the system finds convenient.  However, EXIT_FAILURE
may not be set to 0.

>         exit( err ? EXIT_FAILURE : EXIT_SUCCESS );
> I #defined EXIT_SUCCESS in system.h ostensibly for old sun boxes
> see the comment above the EXIT_FAILURE line in system.h.
If this is catering for pre-standard compilers, then my only
problem with it is that people should get standard C compilers
if they want to compile code on multiple platforms.

> If vms isn't setting EXIT_FAILURE or EXIT_SUCCESS then we
> need to fix the #defines in system.h to do the right thing
> on vms.
If <stdlib.h> doesn't set EXIT_FAILURE or EXIT_SUCCESS, the C
compiler (with libraries) probably has other problems also.
I just don't see how, in December 2000, I can advise using
compilers that do not try to conform to an eleven-year-old

> Also we should not be returning 0, we should be using EXIT_SUCCESS
> in the code in main() in order for the right thing to be done...
Returning 0 is the right thing.  So is returning EXIT_SUCCESS.
Returning anything else would be the wrong thing in a program
expected to run on several different platforms.  (It could be
the right thing to do for a platform-specific program, which
CVS is not.)

> Having said all that I bet this is a moot point in a lot of respects.
> Is anyone even using VMS?
I heard that DEC has dumped all support for the Vaxen, but that
VMS still runs on Alphas.  Some people are still using it,
and are presumably happy with it.

David H. Thornley                          Software Engineer
at CES International, Inc.:  address@hidden or (763)-694-2556
at home: (612)-623-0552 or address@hidden or

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