Xref: utzoo comp.lang.c:20019 comp.bugs.4bsd:1343
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From: greim@sbsvax.UUCP (Michael Greim)
Newsgroups: comp.lang.c,comp.bugs.4bsd
Subject: Is this a bug in some C compilers?
Keywords: bug; cc; referencing a pointer as if it were a structure
Message-ID: <800@sbsvax.UUCP>
Date: 19 Jul 89 09:58:53 GMT
Followup-To: comp.lang.c
Organization: Universitaet des Saarlandes, Saarbruecken, W-Germany
Lines: 72

Hello,
I tried the following program on several machines. IMHO the program
should not compile yet there are some compilers which compile it:

cc 43bsd
cc 43bsd-tahoe
cc ultrix 2.0
cc SunOS 3.5

And there are some that give an error message:

gcc 1.34
cc sinix 2.1 ("McClure")

Here is the program:

---------- cut here ----------------------------
/*
 * What does the compiler do with this?
 */
# include <stdio.h>

struct link {
	struct link * next;
	int count;
};

int fix0;
struct link * t;
int fix1;

main ()
{
	printf ("t lies at %1d, brk is at %1d\n", (int)(&t), (int)sbrk(0));
	printf ("Addresses of %1d byte objects around t : %1d and %1d\n",
		sizeof(int), (int)(&fix0), (int)(&fix1));
	t = NULL;
	t.count = 5;
	if (t.count == 5)
		printf ("Assignment worked.\n");
	else
		printf ("Assignment did not work\n");
	printf ("Value 5 has been put at address %1d\n", &(t.count));
}
---------- cut here ----------------------------

Output from VAX running 43bsd:

Script started on Wed Jul 19 11:44:22 1989
% cc test78.c
"test78.c", line 21: warning: struct/union or struct/union pointer required
"test78.c", line 22: warning: struct/union or struct/union pointer required
"test78.c", line 26: warning: struct/union or struct/union pointer required
% a.out
t lies at 6008, brk is at 6176
Addresses of 4 byte objects around t : 6004 and 6012
Assignment worked.
Value 5 has been put at address 6012
% exit
% 
script done on Wed Jul 19 11:44:47 1989

Am I correct to say that the program is not correct C, and that all compilers
which compile it are wrong?

	-mg

-- 
Michael Greim    Email : greim@sbsvax.informatik.uni-saarland.dbp.de
                 or    : ...!uunet!unido!sbsvax!greim
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