Re: definition of NULL correct?

[Arnaud Lacombe <lacombar%gmail.com@localhost>]

On Tue, Aug 11, 2009 at 7:14 PM, Valeriy E. 
Ushakov<uwe%stderr.spb.ru@localhost> wrote:
> My reading of footnote 71 is that gcc gets the precedence right.
>
>       71)The syntax specifies the precedence of operators  in  the
>          evaluation  of  an  expression,  which is the same as the
>          order of the major subclauses of this subclause,  highest
>          precedence  first.   Thus,  for  example, the expressions
>          allowed as the operands of the binary + operator  (6.5.6)
>          are  those  expressions  defined  in 6.5.1 through 6.5.6.
>          The exceptions are cast expressions (6.5.4)  as  operands
>          of  unary  operators  (6.5.3),  [...]
>
> sizeof is unary expression - 6.5.3, cast is 6.5.4.  The exception
> mentioned is for the production:
>
>    unary-expr: unary-operator cast-expr
>
> and doesn't apply to sizeof.  So
>
>    sizeof (void *) 0
>
> is correctly parsed as uanry-expr: sizeof ( type-name ) leaving the
> "0" as the syntax error.
>
> Neat.  I was always bothered by lack of parens around that cast and
> always wondered if there is a context where it gonna bite us...
>
make sense,  any objection to fix NULL definition ?

--- a/sys/sys/null.h
+++ b/sys/sys/null.h
@@ -5,7 +5,7 @@
 #ifndef        NULL
 #if !defined(__GNUG__) || __GNUG__ < 2 || (__GNUG__ == 2 &&
__GNUC_MINOR__ < 90)
 #if !defined(__cplusplus)
-#define        NULL    (void *)0
+#define        NULL    ((void *)0)
 #else
 #define        NULL    0
 #endif /* !__cplusplus */

 - Arnaud