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From: mouse@mcgill-vision.UUCP
Newsgroups: comp.lang.c
Subject: Re: Disregarding parentheses in C
Message-ID: <762@mcgill-vision.UUCP>
Date: Thu, 7-May-87 04:34:01 EDT
Article-I.D.: mcgill-v.762
Posted: Thu May  7 04:34:01 1987
Date-Received: Thu, 14-May-87 01:33:06 EDT
References: <200@m10ux.UUCP> <6378@mimsy.UUCP> <1038@wanginst.EDU>
Organization: McGill University, Montreal
Lines: 31
Keywords: C parentheses evaluation order parsing

In article <1038@wanginst.EDU>, mckeeman@wanginst.EDU (William McKeeman) writes:
> [begin of quote of x3j11 document July 9, 1986, available from
> Computer and Business Equipment Manufacturers Association, 311 First
> Street, N.W., Suite 500, Washington, DC 20001-2178. (202)737-8888]

> 3.3 EXPRESSIONS
[...]
> An expression [...] may be regrouped [...], provided the types of the
> operands or of the results are not changed by this regrouping.
[...]
> [end of quote]
> [begin comment by McKeeman]
> The only constraint on compiler rearrangements is that the TYPE of
> the operands and results not thereby be changed.  (emphasis mine)

Does this mean that after

extern char _ctypes_[];
#define _ctypes (_ctypes_+1) /* so _ctypes[EOF] is ok */

the compiler is not permitted to change _ctypes['x'] into _ctypes_['y']
because (_ctypes_+1)['x'] <-> *((_ctypes_+1)+'x') cannot be transformed
into *(_ctypes_+(1+'x')) <-> _ctypes_[1+'x']?

(Yes, I realize that in the example above the entire subscripting
operation would (hopefully) computed at compile time.  It was intended
to illustrate a point.)

					der Mouse

				(mouse@mcgill-vision.uucp)