Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!sri-spam!mordor!lll-tis!ptsfa!ihnp4!inuxc!iuvax!bsu-cs!dhesi
From: dhesi@bsu-cs.UUCP
Newsgroups: comp.lang.c
Subject: static char (*b)[6]; /* an unusual declaration */
Message-ID: <761@bsu-cs.UUCP>
Date: Thu, 11-Jun-87 18:51:47 EDT
Article-I.D.: bsu-cs.761
Posted: Thu Jun 11 18:51:47 1987
Date-Received: Sat, 13-Jun-87 11:10:31 EDT
Reply-To: dhesi%bsu-cs@iuvax.UUCP (Rahul Dhesi)
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 37
Summary: b == d but *b != *d.

The April 1987 issue of DEC Professional magazine has this interesting 
example of possible obfuscation in C.

What is the meaning of the following declaration?

     static char (*b)[6];

The compiler and lint checker used by the magazine columnist seem to
treat the declaration of b as equivalent to char ** but the following
strange things happen.

main()
{
     static char (*b)[6];	/* an unusual declaration */
     static char a[] = "Hello";
     char *c = a;
     char **d = &c;
     b = d;			/* So b == d ... Watch. */

     printf ("%s\n", *d);	/* prints "Hello" */
     printf ("%s\n", *b);	/* prints 0 */
}

Other code fragments omitted.  The columnist continues, "...This means
that *b is a constant and while (b) can be modified, *b never will
change its original value.  Thus, setting b = d does not mean that 
*b == *d.  Also, while *b is treated as a constant (unchangeable), the
value of b can vary."

He goes on to ask if other C compiles do the same thing, and wonders
if Ritchie had this in mind when he defined the language.

On our 4.3BSD system, the above code printed the character sequence
"Hello\n^H^T\n" (without quotes).  On my UNIX PC (software revision 3.0) 
it printed "Hello\n\n".
-- 
Rahul Dhesi         UUCP:  {ihnp4,seismo}!{iuvax,pur-ee}!bsu-cs!dhesi