Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: Re: exit(-1) does not work ???
Message-ID: <560@cresswell.quintus.UUCP>
Date: 22 Jan 88 04:39:33 GMT
References: <6935@brl-smoke.ARPA> <7208@ki4pv.uucp> <334@splut.UUCP> <5262@cit-vax.Caltech.Edu>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 64
Keywords: exit, zero
Summary: no, exit(-1) does NOT work.

In article <5262@cit-vax.Caltech.Edu>, wen-king@cit-vlsi.Caltech.Edu (Wen-King Su) writes:
> In article <555@cresswell.quintus.UUCP> ok@quintus.UUCP (Richard A. O'Keefe) writes:
> <original point was that exit(-1) *does not work in UNIX*.  I suggested
> >sticking to 0 and 1 because they *do* work in UNIX *and* in VMS.
> 
> This seems a little strange to me so I decided to check it out.
> Following is a script showing that exit(-1) DOES work in UNIX.
To summarise,
	cat <<EOF >t.c
	main(argc, argv)
	    int argc;
	    char **argv;
	    {
		exit(argc >= 2 ? atoi(argv[1]) : -1);
	    }
	EOF
	cc -o t t.c
He ran this program on a SUN, and claimed that it works.
I too shall run this on a SUN.  Behold!
	Script started on Thu Jan 21 20:09:54 1988
	% csh
	% t ; echo $status
	-1
	% t 254 ; echo $status
	-2
	% exit
	% sh
	$ t ; echo $?
	255
	$ t -2 ; echo $?
	254
	$ exit
	% exit
	script done on Thu Jan 21 20:10:42 1988
To repeat my point, UNIX truncates the argument to 8 bits.  The Bourne
shell treats this as an unsigned char.  The C shell treats this as a
signed char.  Note that on a SUN, according to /usr/include/sys/wait.h
(the include file which describes the termination status result that
is returned to a process's parent) the Bourne shell is right (the
field is described as unsigned short w_Retcode:8;) and the C shell is
wrong.  I don't want to argue for one or the other, only to point
out that they are different, so exit(-1) isn't even portable between
two shells on the same machine!

Wen-King Su also says:
> success, but I believe application programmers should be free to use
> other numbers to their own advantage and OS should provide them with
> the maximum flexibility.  The issue of portability is something each
> programmer has to decide for <arrg!!>self, but it is always useful for
> those who had the experience to point out trouble spots and recommend
> solutions.
Well, yes, but before using other numbers to their own advantage,
application programmers should at least take the trouble to read the
manuals (on a SUN, man 2 exit says explicitly that the low order 8
bits of the status are made available through wait(2), and man 2 wait
points you to <sys/wait.h> where those 8 bits are explicitly declared
to be UNsigned).  I am grateful to Wen-King Su, because I didn't know
about this design bug in the C shell before.  (The manual doesn't say
that status can take negative values, though there is a comment about
adding 0200 which may have some faint connexion.)

Are there any implementations of C in which exit(0) and exit(1) do
NOT work?  Presumably there are, or the ANSI committee wouldn't have
added the new macros (:-), but which are they?