From:	 Morten Welinder <terra@diku.dk>
To:	 linux-kernel@vger.kernel.org, torvalds@transmeta.com
Subject: Type checking MIN with standard interface
Date:	 6 Sep 2001 19:28:15 -0000


All the silent-cast properties of integer types do not apply to
pointers.  Therefore...

-----------------------------------------------------------------------------

cub:~> gcc -O2 -Wall min.c
min.c: In function `main':
min.c:19: warning: comparison of distinct pointer types lacks a cast


cub:~> gcc -O2 -Wall kernel-source.c 2>&1 | \
        grep "comparison of distinct pointer types lacks a cast" | \
        find-and-shoot-programmer

:-)

Morten


-----------------------------------------------------------------------------

#include <stdio.h>

#define MIN(x,y)                                \
  ({ const typeof(x) _x = x;                    \
     const typeof(y) _y = y;                    \
                                                \
     (void) (&_x == &_y);                       \
                                                \
     _x < _y ? _x : _y;                         \
  })

int
main ()
{
  /* Good: */
  printf ("%d\n", MIN((signed)1, (signed)1));

  /* Bad: */
  printf ("%d\n", MIN((signed)1, (unsigned)1));

  return 0;
}

-----------------------------------------------------------------------------
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/