Mon Nov 5 19:12:00 GMT 2012
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org]
> Subject: NULL definition
> Even if you ignore the optional part, the important snippet here is
> that NULL expands to a Null *pointer* value. However, our definition
> of NULL is just 0, so it is of type int. But on many targets
> sizeof(int) is != sizeof(void*). This could potentially result in size
This is not really correct. C defines a "null pointer constant" as any
integral constant expression with value 0 or such an expression cast to
Assigning a null pointer constant to a pointer or comparing a null pointer
constant for equality with a pointer causes the null pointer constant
to assume the proper pointer type.
Literal 0 is a trivial example of a null pointer constant.
If I remember correctly, in C++, NULL must expand to literal 0. In C89,
NULL expands to an implementation-specific null-pointer constant (could be
a literal 0). In C99, NULL must expand to a ((void *) 0).
> So, given that we already rely on stddef.h anyway throughout our header
> files, I wonder if we shouldn't change the definition of NULL by
> including stddef.h as well, so we always get it right:
> #define __need_NULL
> #include <stddef.h>
Won't this introduce additional definitions (offsetof, size_t, ptrdiff_t, ...)
that not all headers defining NULL are specified to define?
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