> a pointer (which (void* )0 is)

In C: the macro NULL is an implementation-defined null pointer constant, which may be

> an integer constant expression with the value ​0​

> an integer constant expression with the value 0 cast to the type void*

In C++: the macro NULL is an implementation-defined null pointer constant, which may be

> an integral constant expression rvalue of integer type that evaluates to zero (until C++11)

> an integer literal with value zero, or a prvalue of type std::nullptr_t (since C++11)