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Subject: Re: include incompatibilities
To: cygwin AT sourceware DOT cygnus DOT com (Cygwin Mailing List)
Date: Wed, 5 Jul 2000 20:17:31 -0700 (PDT)
In-Reply-To: <200007031336.PAA23582@mail.bln1.siemens.de> from "towo@computer.org" at Jul 03, 2000 03:36:35 PM
From: "J. J. Farrell" <jjf AT bcs DOT org DOT uk>
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> From: towo AT computer DOT org
> 
> I had apparently been mislead by the Linux manpage:
> > NAME
> >        perror - print a system error message
> > SYNOPSIS
> >        ...
> >        const char *sys_errlist[];
> >        int sys_nerr;
> > CONFORMING TO
> >        ANSI C, BSD 4.3, POSIX, X/OPEN
> So apparently this manpage is wrong with respect to the "conforming" 
> attributes of these two definitions.

Looks like it's a buggy man page. The conformance statements are
presumably right for perror(), but they're wrong for the others.

> Also, there are some reasons I did not use strerror().
> One is, strerror may depend on setlocale but setlocale is not available 
> on older systems.

I don't understand what you mean by this. If a hosted environment
conforms to C89 then it has strerror(). There is no dependency on
other routines.

> Another is incompatibilities with respect to undefined 
> values:
> Linux:
> > SYNOPSIS
> >        char *strerror(int errnum);
> > RETURN VALUE
> >        The  strerror()  function returns ... an unknown error message 
> >        if the error code is unknown.
> 
> Sun:
> > SYNOPSIS
> >      char *strerror(int errnum);
> > ERRORS
> >      strerror returns NULL if errnum is out-of-range.
> 
> So there is no real standard here either...

The C Standard is that there are no errors. You're only supposed to
pass strerror() values you got from errno, and these are assumed to
always be valid.

X/OPEN extended this by defining strerror() as setting errno to
EINVAL if errnum is not valid. You should set errno to 0 before
calling strerror() then check errno for EINVAL before using the
result. Anything which conforms to X/OPEN XPG3 or later works in
this way, and that includes most versions of UNIX released since
1989 and everything which conforms to UNIX95 or UNIX98.


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