Path: utzoo!utgpu!water!watmath!clyde!rutgers!mit-eddie!uw-beaver!cornell!rochester!ur-tut!sunybcs!boulder!hao!ames!amdcad!sun!pitstop!sundc!seismo!uunet!mcvax!ukc!reading!onion!riddle!domo
From: domo@riddle.UUCP (Dominic Dunlop)
Newsgroups: comp.lang.c
Subject: Re: Address of Array
Summary: I thought I knew about lvalues -- then I discovered ANSI
Keywords: lvalue, modifiable lvalue, & operator
Message-ID: <536@riddle.UUCP>
Date: 23 Dec 87 15:57:31 GMT
References: <126@citcom.UUCP> <2550034@hpisod2.HP.COM> <1854@haddock.ISC.COM> <1442@houdi.UUCP> <9735@mimsy.UUCP>
Reply-To: domo@riddle.UUCP (Dominic Dunlop)
Organization: Sphinx Ltd., Maidenhead, England
Lines: 45

In article <9735@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
[Quotes from other postings deleted]
>Given the declaration
>
>	int a[10];
>
>the following is true:
>
>	0. &a is currently illegal
>	1. &a will be legal in the near future.
[Further points and examples deleted]

Well, I didn't agree with point 1.  Looking at the November 9 draft of
the proposed ANSI standard, I found that it says concisely in 3.3.3.2
-- Address and Indirection Operators:

	The operand of the unary & operator shall either be a function
	designator or an lvalue that designates an object that is not a
	bit-field and is not declared with the register storage class
	specifier.

This confirmed my prejudice, namely that & applied to an object of array 
type is an error.  But then I looked in 3.2.2.1 -- Lvalues and function
designators:

	An lvalue is an expression ... that designates an object...
	A modifiable lvalue is an lvalue that does not have array type...

	Except when it is the operand of the sizeof operator or the unary &
	operator, or is a string literal used to initialize an array of
	characters, an lvalue which has type ``array of type'' is converted
	to an expression that has type ``pointer to type'' that points to
	the initial member of the array object and is not an lvalue.

To summarize, an array can now be an lvalue, albeit not a modifiable one,
and consequently, the & operator can be applied to it.  The draft does not
explicitly say what happens when the operator is so applied.  I assume that
the address of the whole array is delivered, and that the type of the
result is ``pointer to array of ...''  What on earth are the consequences
of this, and why was it done?  Who needs a ``pointer to array of ...''

Enlightenment, please...
-- 
Dominic Dunlop
domo@sphinx.co.uk  domo@riddle.uucp