Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!rex!ames!haven!mimsy!chris
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: is this broken or what?
Message-ID: <22289@mimsy.umd.edu>
Date: 5 Feb 90 09:28:57 GMT
References: <90020407120313@masnet.uucp>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 53

>>... what is the prescribed behavior of
>>        int i=MAXINT, j=(-MAXINT);
>>        if (i > j) printf ("foo");

The ANSI conformant C program

	#include <stdio.h>
	#include <limits.h>

	int main(void) {
		int i = INT_MAX, j = INT_MIN;
		if (i > j) printf("foo\n");
		return 0;
	}

must print `foo' (at least on a hosted implementation).

In article <90020407120313@masnet.uucp> mark.levy@canremote.uucp (MARK LEVY)
writes:
>   I am not up on the ANSI standards that have been proposed, but as
>I recall, the K&R standard was 0 == FALSE and anything else == TRUE.

This is correct, but has nothing to do with the answer to the previous
question.

>>        unsigned int i;
>>        if (i >= 0) ...

>   The use of 2's complement will avoid any kind of problem of 
>positive or negative zero.  A compiler might flag an incompatible
>data type comparison here.  My guess is that if the high order bit
>in i is set, the expression will evaluate false, provided that it
>compiled.

Henry Spencer has already given a correct answer; there is no need for
a false one.  If the variable `i' has ever been set after being created,
the test will always succeed (so that the code given as `...' will be
executed), and indeed, a compiler is free not to generate any code at
all for the test, and to produce a warning.

>   Don't ever assume anything about type conversions.  If you're not
>sure, use pleanty of casts and parens.

If you have a compiler that claims to conform to the ANSI standard, you
can make any assumption that the ANSI standard says must hold.  If you
are working with older compilers, be wary; but in this case you need not
worry: all unsigned numbers are greater than or equal to zero.  The only
way for the code to fail is if i has never been assigned a value: in
such a case it might, e.g., have an `invalid value' type tag that causes
a run-time exception when tested.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris