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From: ado@elsie.UUCP (Arthur David Olson)
Newsgroups: comp.lang.c
Subject: Re: unsigned short vs. negative constant
Message-ID: <7404@elsie.UUCP>
Date: Sun, 3-May-87 17:12:21 EDT
Article-I.D.: elsie.7404
Posted: Sun May  3 17:12:21 1987
Date-Received: Tue, 5-May-87 01:18:08 EDT
Followup-To: poster
Organization: NIH-LEC, Bethesda, MD
Lines: 34

Thanks to everyone who replied to replied to my question about what the code
	#include "stdio.h"

	main()
	{
		unsigned short	us;

		us = ~0;
		(void) printf("%d\n", us == -1);
	}
should print on systems where sizeof short < sizeof int,
and what it actually does print on various systems.  The scoop:

*	Some systems simply print 1,
	including Elsie herself (a VAX 11-750 running MORE/bsd 4.3),
	a VAX 11-780 running 4.3 BRL UNIX, and an Ultrix 1.2 system.
*	Other systems systems simply print 0, including KCC on TOPS-20,
	an AT&T 3B5 running System V Release 2.0.1 3B5 Version 2,
	an a "moto '030 machine running System V.2."
*	The latest Sun systems print 1; issuing a warning during compilation.
*	A Concurrent system prints 0; it issues a warning during compilation.
	Sun systems may do this in the future.
	Saber-C prints 0; it issues a warning.
*	K&R can't be used to resolve the issue, since it predates unsigned
	shorts.
*	The consensus of opinion is that under X3J11's "value-preserving"
	widening rules, the program should print 0.

The moral of the story: folks who maintain the various versions of lint may
want to have it look for and warn about such code, at least when lint is run in
"check portability" mode.
-- 
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