NULL - null pointer constant

SYNOPSIS

#include <stddef.h> #define NULL ((void *) 0)

DESCRIPTION

NULL represents a null pointer constant, that is, a pointer that does not point to anything.

CAVEATS

It is undefined behavior to dereference a null pointer, and that usually causes a segmentation fault in practice. It is also undefined behavior to perform pointer arithmetic on it. NULL - NULL is undefined behavior, according to ISO C, but is defined to be 0 in C++. To avoid confusing human readers of the code, do not compare pointer variables to 0, and do not assign 0 to them. Instead, always use NULL. NULL shouldn’t be confused with NUL, which is an ascii(7) character, represented in C as ‘\0’.