Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: exit(-1)
Message-ID: <502@cresswell.quintus.UUCP>
Date: 31 Dec 87 07:17:08 GMT
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 28
Keywords: negative exit values inadvisable

I just installed a program which came over one of the *sources*
newsgroups.   The accompanying README was extremely funny:  it said
    The program should be owned by root and suid.
But that's not a C joke.  What is of interest here is its use of exit().

It used exit() in two ways:
	exit(1)		/* can't find datum in file */
	exit(-1)	/* can't fopen file, either "r" or "w" */
Oddly enough, it did not use exit(0) at the end of main().

Given all the hoo-haa we've been having about exit() recently, I
thought it might not be out of place to warn people that the value
given to exit() is often truncated to 8 bits on the way out.  For
example, in UNIX, for which this program was intended, saying
	this-program some-argument
	if [ #? -eq -1 ] ; then
	    ...
	fi
will NEVER succeed, because the return value is going to be 255.
The VAX-11 C manual explicitly says that the argument of exit()
should be 0 or a value errno might have.

The Oct86 dpANS said only that 0 arguments indicate success and
non-0 arguments indicate failure in some system-dependent way.

Except where you are writing code for a specific system (say you
have #if cases for MVS, VMS, and UNIX) it seems like a good idea
to pass only 0 or 1 to exit().