c - Is NULL a pointer?

Question

So, I had an argument with my professor earlier defending that NULL is not a pointer, but he kept on insisting that it is because there is such a thing as NULL pointer. So, here I am now a little bit confused if NULL is really a pointer or not

I already tried search over the internet but couldn't find any answer, so my last resort is here

Answer 1

In C, NULL is a macro that expands to a null pointer constant.

7.19p3

The macros are

NULL which expands to an implementation-defined null pointer constant; ...

A null pointer constant is an integer constant expression with the value 0 ( e.g., 0, 1-1, 42*0LL, etc.) or such an expression cast to (void*).

6.3.2.3p3

An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.66) If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.

Most common C implementations define NULL to be 0, 0L, or ((void*)0).

So you are correct. NULL need not be a pointer.

(IIRC, C++ doesn't even allow the (void*) cast in NULL, meaning NULL in C++ always has integer type. Because of that and because void* pointers do not compare with regular pointers so readily in C++, C++>=11 now has a special nullptr keyword.)