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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.wizards,comp.lang.c
Subject: Re: have I found a bug in K&R?
Message-ID: <9031@mimsy.UUCP>
Date: Sun, 18-Oct-87 12:22:09 EDT
Article-I.D.: mimsy.9031
Posted: Sun Oct 18 12:22:09 1987
Date-Received: Mon, 19-Oct-87 01:49:32 EDT
References: <18668@amdcad.AMD.COM> <517@hubcap.UUCP> <321@laticorp.UUCP> <3802@elecvax.eecs.unsw.oz>
Followup-To: comp.lang.c
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 39
Xref: mnetor comp.unix.wizards:4984 comp.lang.c:5005

(This discussion should have been in comp.lang.c; followups have
been directed there.)

In article <3802@elecvax.eecs.unsw.oz> cameron@elecvax.eecs.unsw.oz
(Cameron Simpson) writes:
>... An lvalue is something which may occur on the left-hand side of an
>assignment statement.  If I say
>	char s[];	/* a character array of unspecified size */
>	char *t;	/* a pointer to a character */
>then I may say `t++;' or `t = s;' or `t = &s[2];' and so on.
>I may not say `s++;' or `s = t;'.

True enough, except . . . .

>This applies whether they are declared as formal parameters or as
>external array declarations. I often declare functions like
>	fn(a,b)
>	char *a;
>	char b[];
>in order to *prevent* myself from changing b during the function.

. . . this does not work in (some? many? most? all?) compilers.
PCC is perfectly happy with `b = a' inside the code for `fn'.
I am not sure whether the draft has anything to say on the subject.

Incidentally, with the addition of `const', ANSI now has the
concept of `modifiable lvalues', so that in

	const int n = 4;

`n' is an lvalue, but not a modifiable lvalue.  (At least, I think
this is how it works---there are odd possibilities like

	const volatile int *clockaddr = (int *)CLOCK_ADDRESS;

that I am still not sure about.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris