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From: throopw@rtp47.UUCP (Wayne Throop)
Newsgroups: net.lang.c,net.unix-wizards
Subject: Re: Re: PCC, lint bug
Message-ID: <178@rtp47.UUCP>
Date: Mon, 9-Sep-85 19:58:59 EDT
Article-I.D.: rtp47.178
Posted: Mon Sep  9 19:58:59 1985
Date-Received: Wed, 11-Sep-85 07:49:43 EDT
References: <1152@brl-tgr.ARPA> <81@copper.UUCP> <10287@ucbvax.ARPA>
Followup-To: net.lang.c
Organization: Data General, RTP, NC
Lines: 49
Xref: watmath net.lang.c:6331 net.unix-wizards:14788

> I'm disgusted at the number of 'wizards' who are confused.
> 'x' should best be though of as a pointer to array of two ints.
> int   y[2][2][2]; /* y should best be thought of as a pointer to
>                       two dimentional array of ints ([2][2]) */
> int   yp[][2][2] = y; /* is a proper pointer */
>                       Jeff Anton ucbvax!anton anton@BERKELEY.EDU

Now wait a minuite.  As near as I can tell from this fragment, Jeff is
as confused as any other wizard.  Since an initializer is used in the
declaration

        int yp[][2][2] = y;

yp is clearly *not* a formal.  And this being the case, *yp* *is* *not*
(I repeat *not*) a pointer.  I assume what is meant to happen for the
two above declarations is

        int y[2][2][2];
        int (*yp)[2][2] = y;

The abomination Jeff gave above declares yp to be an array of 1
array of 2 array of 2 integers, and (if the compiler doesn't choke)
initializes yp[0][0][0] to be the expression (int)y.  Yuck.

I tried this C file on SysV lint:

    int x1[2][2];
    int x2[][2] = x1;  /* I hope lint complains here */

    int (*x3)[2] = x1; /* I hope lint doesn't complain here */

And lint quite properly complained, saying:

    warning: illegal combination of pointer and integer:
        (2)  operator =

It is interesting that pointer/array equivalence causes such problems,
when it it really so simple.   The *only* (I repeat *only*) place where
a declarator like "int x[]" declares x to be a pointer is in *formal*
declarations.  In static, external, or automatic declarations, *x* *is*
*an* *array* (of compiler or loader determined size).  And even in
formal declarations, x "should be" *thought of* as an array.

--
Note that Followup-To specifies net.lang.c
--
"People who live in glass houses, shouldn't"
-- 
Wayne Throop at Data General, RTP, NC
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