Re: NULL

[Rich Felker <dalias@aerifal.cx>]

On Sun, Jan 13, 2013 at 01:46:28PM -0600, Rob Landley wrote:
> On 01/13/2013 11:47:32 AM, Szabolcs Nagy wrote:
> >> So I think you're saying is that the behavior I'm depending on
> >changed?
> >
> >well,
> >
> >(int)(void*)0 is not an "integer constant expression" and it
> >is not a "null pointer constant",
> 
> C99 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.
> 
> 7.17 #3: The macros are NULL which expands to an
> implementation-defined null pointer constant;
> 
> So it uses "constant" in the name but either it's not a constant or
> typecasting it twice makes it stop being a constant.

Basically, the latter. It may still be a constant, but it's neither an
integer constant expression (this is a very restricted category of
expressions) not a null pointer constant.

In any case, this thread has gotten WAY off-topic, going all over the
place into territory about the merits and demerits of different
languages and anti-FSF politics. Those topics may be worth discussing
in some contexts, but it seems to have left everybody really confused
about the issues at hand, which are:

- whether we should work around broken programs that pass NULL to
  variadic functions

- and if so, how

The emerging consensus seems to be using

#define NULL 0L

unconditionally in both C and C++ mode.

Rich