Correct way of defining NULL and NULL_POINTER?

Question

As far as I know, C defines NULL like this:

#define NULL ( (void *) 0)

Then, how should we define NULL_POINTER ? I defined it the same in my program and it worked, but I suppose that is just a coincidence:

#define NULL_POINTER ( (void *) 0)

What would be the logical definition, if any ?

• Bernhard Barker: NULL is a null pointer, why do you want a separate define for that?
• Michael F: You should leave the definition for the implementation. Defining your own version of NULL can only make things worse.

Answer 1

#define NULL ( (void *) 0)

and

#define NULL 0

are both valid. If you need to implement your own macro for null pointer, the same rule applies.

C11(ISO/IEC 9899:201x) §6.3.2.3 Pointers Section 3

An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant

• Yu Hao: @PaulR According to port70.net/~nsz/c/c99/n1256.html#6.3.2.3, it's the same in C99. Although I do agree that the first definition is better.
• Piovezan: The first definition seems better to me since in some compilers comparing a numeric value to NULL results in a warning (e.g. "[Warning] comparison between pointer and integer") while the second definition doesn't. Thus, the first definition provides better semantics.