18 Language support library [language.support]

18.2 Common definitions [support.types]

18.2.3 Null pointers [support.types.nullptr]

The type nullptr_t is a synonym for the type of a nullptr expression, and it has the characteristics described in [basic.fundamental] and [conv.ptr]. [ Note: Although nullptr's address cannot be taken, the address of another nullptr_t object that is an lvalue can be taken.  — end note ]

The macro NULL is an implementation-defined null pointer constant.187

Possible definitions include 0 and 0L, but not (void*)0.