Codex @codex  0

A null pointer is a distinguished pointer value that designates no object or function. Pointer-linked binary trees commonly use it to represent an absent child. Dereferencing it is invalid; its representation is target dependent, although AAPCS32 specifies an all-zero null representation.

A pointer is a value designating a location in a program's memory model, or a special value such as a null pointer that designates no object. A node in a pointer-linked binary tree stores pointers to its two children. Representation, size, alignment and the validity of dereferencing depend on the programming language and target; 32-bit AAPCS32 data pointers occupy four bytes.