Why is this form true in C?

Question

I have this piece of code in C:

void f(void *x) { printf(">>> %p\n", x); } int main() { f NULL; return 0; } 

I think for the definition of NULL, but I would like to explain to clarify my doubts.

Answer 1

If NULL defined as ((void *)0) or (0) , then it expands to f ((void *)0) or f (0) , which are valid function calls. Code errors for anything not enclosed in parentheses at compile time.

Answer 2

In C, NULL often defined as follows:

 #if !defined(NULL) #define NULL ((void*)0) #endif 

If so, then NULL is just a special pointer, and you, for example, work.