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* [Bug c/30260]  New: Enumeration types and enumeration constants erroneously given unsigned types
@ 2006-12-19 20:51 rda at lemma-one dot com
  2006-12-19 21:06 ` [Bug c/30260] " pinskia at gcc dot gnu dot org
                   ` (8 more replies)
  0 siblings, 9 replies; 10+ messages in thread
From: rda at lemma-one dot com @ 2006-12-19 20:51 UTC (permalink / raw)
  To: gcc-bugs

The comments at the top of the following source file describes the bug.
This happens on gcc 4.1.0 too. for what it is worth, uname -a and
gcc -v output for the Linux box I am currently using are at the end.
The actual code is only 14 lines and only includes stdio.h.

/* source file: enum_bug.c
 *
 * An anomaly in gcc C: according to C99 6.7.2.2, enumeration constants
 * must have signed int type and, if some enumeration constant has
 * a negative value, then the integer type compatible with the
 * enumeration type must be a signed type. It seems to be possible
 * to fool gcc into misapplying these rules by making the type of
 * the integer constant expression giving the value of an enumeration
 * constant an unsigned integer type. This was first observed in a case
 * where the expression involved sizeof, but just a cast to unsigned or using
 * an unsigned integer constant has the same effect as seen below:
 *
 * This has been observed on various Linux PCs and on Mac OS X with
 * several versions of gcc (3.4.1 up to 4.1.0).
 *
 * Compiling and running with
 *
gcc -o enum_bug enum_bug.c ; ./enum_bug
 *
 * produces no diagnostics and code that prints out the following:
 *
(a < 0) = 1, (A2 < 0) = 1, A{1,2} = +0, -1
(b < 0) = 0, (B2 < 0) = 0, B{1,2} = +0, -1
 *
 * Compiling and running with:
 *
gcc -ansi -pedantic -o enum_bug enum_bug.c; ./enum_bug
 *
 * results in an an incorrect warning
 *
enum_bug.c:38: warning: ISO C restricts enumerator values to range of `int'
 *
 * but with code that correctly prints out:
 *
(a < 0) = 1, (A2 < 0) = 1, A{1,2} = +0, -1
(b < 0) = 1, (B2 < 0) = 1, B{1,2} = +0, -1
 *
 * Rob Arthan (rda at lemma-one dot com) 19th December 2006
 */

#include <stdio.h>
enum A {A1 = 0, A2 = A1 - 1};
enum B {B1 = 0u, B2 = B1 - 1};
int main(void)
{
    enum A a = -1;
    enum B b = -1;
    printf("(a < 0) = %d, (A2 < 0) = %d, A{1,2} = %+d, %+d\n",
        (int)(a < 0), (int)(A2 < 0), (int)A1, (int)A2);
    printf("(b < 0) = %d, (B2 < 0) = %d, B{1,2} = %+d, %+d\n",
        (int)(b < 0), (int)(B2 < 0), (int)B1, (int)B2);
    return 0;
}
/*
 * uname -a:
Linux localhost 2.6.8.1-12mdk #1 Fri Oct 1 12:53:41 CEST 2004 i686 Pentium III
(Coppermine) unknown GNU/Linux

 * gcc -v:
Reading specs from /usr/lib/gcc/i586-mandrake-linux-gnu/3.4.1/specs
Configured with: ../configure --prefix=/usr --libdir=/usr/lib
--with-slibdir=/lib --mandir=/usr/share/man --infodir=/usr/share/info
--enable-shared --enable-threads=posix --disable-checking --enable-long-long
--enable-__cxa_atexit --enable-clocale=gnu --disable-libunwind-exceptions
--enable-languages=c,c++,ada,f77,objc,java --host=i586-mandrake-linux-gnu
--with-system-zlib
Thread model: posix
gcc version 3.4.1 (Mandrakelinux 10.1 3.4.1-4mdk)
 */


-- 
           Summary: Enumeration types and enumeration constants erroneously
                    given unsigned types
           Product: gcc
           Version: 3.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rda at lemma-one dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30260


^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2008-10-19 13:56 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2006-12-19 20:51 [Bug c/30260] New: Enumeration types and enumeration constants erroneously given unsigned types rda at lemma-one dot com
2006-12-19 21:06 ` [Bug c/30260] " pinskia at gcc dot gnu dot org
2006-12-19 21:22 ` joseph at codesourcery dot com
2006-12-19 21:23 ` jsm28 at gcc dot gnu dot org
2008-02-12 14:26 ` manu at gcc dot gnu dot org
2008-02-15 11:26 ` manu at gcc dot gnu dot org
2008-08-23 18:21 ` manu at gcc dot gnu dot org
2008-08-24 14:03 ` rda at lemma-one dot com
2008-10-19 13:54 ` manu at gcc dot gnu dot org
2008-10-19 13:56 ` manu at gcc dot gnu dot org

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