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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: *&aptr , &*aptr question
Date: Tue, 14 Jun 2016 16:51:03 -0700
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BartC <bc@freeuk.com> writes:
[...]
> What's going on here then:
>
> int* Ptr;
>
> Ptr = Ptr;
> Ptr = *Ptr;
> Ptr = &Ptr;
> Ptr = &*Ptr;
> Ptr = *&Ptr;
>
> Ptr = &*&Ptr;
> Ptr = *&*Ptr;
>
> Ptr = &*&*Ptr;
> Ptr = *&*&Ptr;
>
> These are all fine according to gcc (and TCC and clang; other compilers 
> aren't quite so happy).

What do you mean by "fine"?  Did you not get warnings?

gcc is notorious for issuing non-fatal warnings by default for some
constraint violations.  Surely you've seen that mentioned here before.

I get:

c.c: In function ‘main’:
c.c:7:9: warning: assignment makes pointer from integer without a cast
[enabled by default]
     Ptr = *Ptr;
         ^
c.c:8:9: warning: assignment from incompatible pointer type [enabled by
default]
     Ptr = &Ptr;
         ^
c.c:12:9: warning: assignment from incompatible pointer type [enabled by
default]
     Ptr = &*&Ptr;
         ^
c.c:13:9: warning: assignment makes pointer from integer without a cast
[enabled by default]
     Ptr = *&*Ptr;
         ^

If you really didn't get any warnings, what version of gcc are you
using?

If you did, why the &*&* didn't you mention that fact?  (Use the
-pedantic-errors option if you want fatal errors for constraint
violations.)

(Of course the standard only requires a diagnostic message, so this
isn't a conformance violation.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"