Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!ulysses!allegra!mit-eddie!ll-xn!ames!sdcsvax!ucsdhub!hp-sdd!hplabs!hpcea!hpfcdc!boemker
From: boemker@hpfcdc.UUCP
Newsgroups: comp.lang.c
Subject: Re: Question about type casting
Message-ID: <5080011@hpfcdc.HP.COM>
Date: 13 Jan 88 18:49:57 GMT
References: <546@xyzzy.UUCP>
Organization: HP Ft. Collins, Co.
Lines: 26
Posted: Wed Jan 13 13:49:57 1988

> But even if we accept the dubious legality of the cast, which is
> justified only by very broad interpretation of K&R, (how do you convert
> a pointer-valued expression to an array-valued expression, anyway?), the
> resulting expression being subscripted would have to be a temporary
> array (with, for this reason, no aliases), and the whole assignment
> becomes a monumentally obfuscated no-op.  (In particular, it does *NOT*
> by any remote stretch of the imagination initialize i.)

> But clearly K&R did not intend to allow anything to be cast to array
> type, since casts are defined as conversions, and the allowable
> conversions do not include any that result in arrays.

1. I'm not so sure about K&R's intentions.  True, a cast is a conversion, but
   the book does not explicitly define the set of legal conversions; it only
   lists conversions.  The list is not necessarily complete.

2. Whenever an array identifier appears in an expression, it is treated as
   being a pointer to the first element of the array.  Casting an expression
   as an array is just asking that expression to be used as a pointer to the
   base element of a (mutli-dimensional) rectangular collection of elements.
   Using an expression of type array is defined, and the object referenced
   is not the whole collection of elements but a pointer to the collection
   (pp. 195 bottom and 210 top).  Saying that the resulting expression would
   have to be a temporary array does not make sense under K&R, and it shows
   a misunderstanding of its concept of arrays: every array expression of
   the form A[i] is equivalent to the pointer expression *(A+i).