The macro NULL, defined in any of <clocale> ([c.locales]), <cstddef> ([cstddef.syn]), <cstdio> ([cstdio.syn]), <cstdlib> ([cstdlib.syn]), <cstring> ([cstring.syn]), <ctime> ([ctime.syn]), or <cwchar> ([cwchar.syn]), is an implementation-defined C++ null pointer constant in this International Standard ([support.types]).