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 6.3.2.3 "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 > > -- > David Laight: da...@l8s.co.uk > >
