NULL3const

Usage

#include <stddef.h>

Library

Standard C library (libc)

Overview

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

Notes

The following headers also provide NULL: <locale.h>, <stdio.h>, <stdlib.h>, <string.h>, <time.h>, <unistd.h>, and <wchar.h>.

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'.