[cdellin]

Just a correction: the code is actually perfectly portable. The integer constant 0 is the canonical definition of the null pointer by definition in the standard (See Section 6.2.2.3 "Pointers" in C89). The null pointer constant (NULL) is defined primarily for convenience (so a reader knows you mean a null pointer instead of a arithmetic zero). Of course, the bitwise representation of the null pointer need not be all-bits-zero; that is, NULL = (void )0 != ((int *)&0).

[adestefan]

I stand corrected, it does define the integer constant 0 to be promoted to the null pointer. In C11 this is Section 6.3.2.3. To make it even more confusing Section 7.19 Common Definitions <stddef.h> defines NULL to be an implementation depefined null pointer constant.

I was always taught that (void *)0 is a valid definition of NULL, but that 0 was not necessarily.