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From: throopw@dg_rtp.UUCP
Newsgroups: comp.lang.c,comp.bugs.4bsd
Subject: Re: Bad Pointer Declaration in 'scandir'
Message-ID: <1575@dg_rtp.UUCP>
Date: Sat, 4-Apr-87 14:47:45 EST
Article-I.D.: dg_rtp.1575
Posted: Sat Apr  4 14:47:45 1987
Date-Received: Sun, 5-Apr-87 21:58:27 EST
References: <2479@dalcs.UUCP> <5916@mimsy.UUCP> <2491@dalcs.UUCP>
Lines: 43
Xref: utgpu comp.lang.c:1476 comp.bugs.4bsd:273

> dalegass@dalcs.UUCP (Dale Gass)>
>> chris@mimsy.UUCP (Chris Torek)

>>>  struct direct *(*namelist)[];
>> No: for there is no such thing.  A declaration for a pointer to an
>> array must specify the size of the array.  In fact, what both the
>> code and the manual *should* say is
>> 	struct direct ***namelist;
> I disagree with this.  I think a pointer to an array need not specify the
> array size.

I'll stay out of the does-the-array-size-need-to-be-specified argument
for the most part, though I will note in passing that K&R and H&S allow
it to be absent, while draft X3J11 does not.  Most compilers allow it to
be absent, but some do not.  Thus, the wise portability-minded,
starndard-complient coder will avoid such constructs, and replace them
with the equivalent pointer constructs.  Which is where *I* disagree
with Chris.  Unusual as it is for Chris to make a mistake, he has made a
doozy here (though an easy doozy to make, so to type).

In particular, the claim that *(*foo)[], which is a pointer to an array
of pointers, should be replaced by ***foo, which is a pointer to a
pointer (or an array of pointers) to a pointer (or an array of pointers)
is WRONG, WRONG, WRONG!  Look at the memory layouts implied by these
constructs.  *(*foo)[] is talking about THREE kinds of objects.  (1) A
pointer, (2) an array, and (3) the objects that the array of pointers
point to.  ***foo, on the other hand, is talking about FOUR kinds of
objects.  (1) A pointer, (2) the pointer (1) points to, (3) the pointer
(2) points to, and (4) {finally} the object that (3) points to.  A
completely and utterly different memory layout.

Be careful folks.  Pointers aren't arrays, and arrays are not pointers,
and even the experts (such as Chris) can *sometimes* get confused as to
where a [] declaration part can and should be simply replaced by a *
declaration part.

--
"I like you.  You're warm and compassionate, like my father."
                                --- Stingray (speaking to the "good cop"
                                              of a pair of poplicemen trying
                                              to get 'ray to "talk")
-- 
Wayne Throop      <the-known-world>!mcnc!rti-sel!dg_rtp!throopw