Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!unido!mikros!mwtech!martin
From: martin@mwtech.UUCP (Martin Weitzel)
Newsgroups: comp.lang.c
Subject: "array" vs. "&array" ?
Message-ID: <571@mwtech.UUCP>
Date: 22 Dec 89 21:04:13 GMT
References: <1989Dec22.013757.3086@sj.ate.slb.com>
Reply-To: martin@mwtech.UUCP (Martin Weitzel)
Organization: MIKROS Systemware, Darmstadt/W-Germany
Lines: 74
Keywords:

Some days ago I posted a question if it is legal (or makes sense)
to write a "&" before an array. I received a few responses, some
mentioned, that an "&" before an array is illegal and/or that the
compiler simply ignores it.

I will not object to this - my compiler with ISCs 386/ix also ignores
it - but I will present you a fragment of C-Code, which can not be
compiled (without warnings) with this type of compilers.

To my understanding, the following *is* a type mismatch:
-----------------------------------------------------------------------
main()
{
	char a[10], (*p)[10];

	p = a;
warning: illegal pointer combination, op =
}
-----------------------------------------------------------------------
The compiler seems to take my point of view.

Then I'll try to get it right (to my understanding):
-----------------------------------------------------------------------
main()
{
	char a[10], (*p)[10];

	p = &a;
warning: & before array or function: ignored
warning: illegal pointer combination, op =
}
-----------------------------------------------------------------------
Now, what's that? I've made it right, then the compiler throws out
my "&" and complains that it is wrong. Of course it is wrong now,
the compiler just *made* it wrong!

And to all of you who want to now, why I might want to do such strange
things, look at the following:
-----------------------------------------------------------------------
main()
{
	char m[20][10], (*p)[10];

	p =  m[0];
	/*  ^ to "&" or not to "&", that is the question */
	
	/* do something with (*p)[x] -- a single char
	   and have the possibility to increment p to
           point to the next group of 10 char-s */
}
-----------------------------------------------------------------------
or another one:
-----------------------------------------------------------------------
char (*foo())[10]
{
	static char m[20][10] = {
		/* some initialization */
	};
	int i;
	/* do some calculations giving a value to i */
	return  m[i];
	/*     ^ to "&" or not to "&", that is the question */
}
-----------------------------------------------------------------------
I simply can't get it right! What am I missing?

Or is the compiler, that ignores the &, something missing?

(OK, before you post it: I *know* that I can supress the warning
with a typecast, but I think typecasts should only be used as
last resort and not be necessary if you want nothing more than
a perfectly legal and reasonable assignment or function return!)
-- 
Martin Weitzel, email: martin@mwtech.UUCP, voice: 49-(0)6151-6 56 83