Newsgroups: comp.lang.c
Path: utzoo!sq!msb
From: msb@sq.sq.com (Mark Brader)
Subject: Re: Can analysis detect undefined expressions?
Message-ID: <1991Jun23.060337.26567@sq.sq.com>
Organization: SoftQuad Inc., Toronto, Canada
References: <14489.2861906B@stjhmc.fidonet.org>
Date: Sun, 23 Jun 91 06:03:37 GMT
Lines: 20

> >      (j = ((i=1) == (i=2))) == (j = ((i=3) == (i=4)))
> Not arguing that the result is undefined as you say.  But....  I for one
> would quickly scrap any compiler that went to the additional work of 
> embedding code to yield a value of anything other than 1,2,3 or 4 for i.

On the other hand, I for one would welcome with open arms a compiler
that made those checks at compile time and exercised its right to
*refuse to compile it* in the first place.

(As has been pointed out, this becomes arbitrarily difficult if the
expression involves things like indirection.  I don't care.  I just
want the compiler to reject a[i++] = i, x = a[i++]+b[i++], the above
expression, and other such cases that *are* easily diagnosed.  Even
Saber-C (3.0.1) misses these, unless maybe I have some option set wrong.)
-- 
Mark Brader		     "It is impractical for the standard to attempt to
SoftQuad Inc., Toronto	      constrain the behavior of code that does not obey
utzoo!sq!msb, msb@sq.com      the constraints of the standard."  -- Doug Gwyn

This article is in the public domain.