Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!ucsd!ucbvax!decwrl!decvax!tektronix!nosun!lfm.fpssun.fps.com!lfm
From: lfm@fpssun.fps.com (Larry Meadows)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran versus C for numerical analysis
Summary: not required to catch it
Message-ID: <316@lfm.fpssun.fps.com>
Date: 13 Sep 88 21:23:41 GMT
References: <408@marob.MASA.COM> <3417@lanl.gov> <410@marob.MASA.COM>
Organization: Floating Point Systems
Lines: 21

In article <410@marob.MASA.COM>, samperi@marob.MASA.COM (Dominick Samperi) writes:

>  [...]                             FORTRAN: "do not modify the same array
> by two different aliases," since both rules have in common the fact that
> the compiler will not make sure you obey them (though FORTRAN compilers
> are supposed to catch this error, I haven't seen any that do).

I know we have beaten this dead horse to death, but I just can't
resist.  The FORTRAN ANSI-77 standard says that the behavior in this
case is undefined.  It does not, repeat not, ..., repeat not state,
imply, or suggest that a compiler is required to detect this error, any
more than it is required to detect assignment to a constant passed as
an actual parameter, different length common blocks with the same name,
ad nauseum.  What it means is that a standard-conforming compiler can
assume that these rules are not violated and perhaps optimize the code
better as a result.  Of course, some of these rules are violated so
often that compiler writers, to satisfy their users, must treat the
violations as de facto extensions to the standard.
-- 
Larry Meadows @ FPS			...!tektronix!fpssun!lfm
					...!nosun!fpssun!lfm