[Qemu-devel] [PATCH] Fix definition of NULL

[Qemu-devel] [PATCH] Fix definition of NULL

[Stefan Weil]

[-- Attachment #1: Type: text/plain, Size: 263 bytes --]

Hello,

the definition of NULL in dyngen-exec.h is correct for C++
but wrong for C. It results in a compiler warning.

My patch fixes it. Because Qemu does not support C++,
I just used the C definition and did not try to support
C++, too.

Regards
Stefan Weil




[-- Attachment #2: null.patch --]
[-- Type: text/x-diff, Size: 496 bytes --]

Fix declaration of NULL.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>

Index: trunk/dyngen-exec.h
===================================================================
--- trunk.orig/dyngen-exec.h	2009-02-06 22:15:33.000000000 +0100
+++ trunk/dyngen-exec.h	2009-02-06 22:16:03.000000000 +0100
@@ -91,7 +91,7 @@
 extern int fputs(const char *, FILE *);
 extern int printf(const char *, ...);
 #undef NULL
-#define NULL 0
+#define NULL ((void *)0)
 
 #if defined(__i386__)
 #define AREG0 "ebp"

Re: [Qemu-devel] [PATCH] Fix definition of NULL

[M. Warner Losh]

In message: <498CA9B6.5080302@mail.berlios.de>
            Stefan Weil <weil@mail.berlios.de> writes:
: Hello,
: 
: the definition of NULL in dyngen-exec.h is correct for C++
: but wrong for C. It results in a compiler warning.
: 
: My patch fixes it. Because Qemu does not support C++,
: I just used the C definition and did not try to support
: C++, too.

Actually, it is correct for C as well.  "#define NULL 0" is a
perfectly acceptable definition[*].  Your definition is also correct,
since there are two valid NULL pointer definitions in 'C'.  Which one
you use will determine which class of errors you catch, but neither
one will catch all errors.

which compilers is it generating warnings on and what are the
warnings?

Warner

[*] C9x section 3.2.3 para 3 states:

       [#3] An integer constant expression with  the  value  0,  or
       such  an  expression  cast  to type void *, is called a null
       pointer constant.

with a footnote that says NULL is defined in stddef.h.