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From: DHowell.ElSegundo@Xerox.COM
Newsgroups: comp.lang.c
Subject: Re: Weird C code as test for employment
Message-ID: <8771@brl-adm.ARPA>
Date: Wed, 12-Aug-87 19:12:47 EDT
Article-I.D.: brl-adm.8771
Posted: Wed Aug 12 19:12:47 1987
Date-Received: Sat, 15-Aug-87 02:33:57 EDT
Sender: news@brl-adm.ARPA
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In some previous article, someone wrote:
...
>char *c[] = { "ENTER", "NEW", "POINT", "FIRST" };
>char **cp[] = { c+3, c+2, c+1, c };
>char ***cpp = cp; 
      [extra asterisk deleted]
...
>    printf("%s ", *--*++cpp+3);

In article <6253@brl-smoke.ARPA> Doug Gwyn <gwyn@brl-smoke.arpa> writes:
>In article <183@xyzzy.UUCP> throopw@xyzzy.UUCP (Wayne A. Throop)
writes:
>>I don't get it.  What lvalue rules are violated by the above?

>What I originally thought might be wrong is that in the process of
>expanding the expression *--*++cpp at one point one is trying to
>evaluate --(cp+2) (or something like that), and it was not (and still
>is not) clear to me that (cp+2) qualifies as a modifiable lvalue.
>Perhaps one can deduce this from the rules but I sure didn't.

The expression would be grouped as (*(--(*(++cpp))))+3, so the operand
to -- is (*(++cpp)).  Before the expression, (due to a previous ++cpp)
the value of cpp was &cp[1].  ++cpp changes this to &cp[2].  *++cpp is
thus *&cp[2], which is cp[2], which is as far as I know an acceptable
lvalue.  So the obfuscated expression is not illegal.  But I wouldn't
mind if legislation were passed making it so. :-)

Dan <DHowell.ElSegundo@Xerox.COM>

DISCLAIMER: "My opinions are not Xerox copies!"