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Re: CVS commit: src

On Sep 2, 2011, at 11:09 AM, David Laight wrote:

On Thu, Sep 01, 2011 at 08:19:07AM +0100, Iain Hibbert wrote:
On Wed, 31 Aug 2011, Warner Losh wrote:

In the absence of both the prototype and a cast, NULL (which can be 0)
will be passed as an int, not as a pointer.

NetBSD C headers define NULL as ((void *)0), and our Makefiles use -Wall
(includes -Wimplicit-function-declaration) to avoid such situations..

ISTR that ansi C (or some recent version of it) does require that
NULL be a pointer constant - so that it gets passed correctly to
varargs functions that expect a data pointer.

C89 and C99 don't require this.  #define NULL 0 is a conforming definition.

C1X draft N1570 still has "An integer constant _expression_ with the value 0, or such an _expression_ cast to type void *, is called a null pointer constant." and 7.19 "The macros are NULL which expands to an implementation-defined null pointer constant" which means #define NULL 0 is still a conforming definition.

C++'s new standard is different though.

Without function prototypes this is a bigger problem, especially
since (char *)0 isn't a useful definition!
This is where 'lint' comes in handy, since it (effectively) checked
that args matched the inferred prototype ...


David Laight:

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