NAME

       NULL - null pointer constant

LIBRARY

       Standard C library (libc)

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.

CONFORMING TO

       C99 and later; POSIX.1-2001 and later.

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'.

BUGS

       When it is necessary to set a pointer variable to a null pointer, it is not enough to  use
       memset(3)  to  zero  the pointer (this is usually done when zeroing a struct that contains
       pointers), since ISO C and POSIX don't guarantee that a bit pattern of all 0s represent  a
       null pointer.  See the EXAMPLES section in getaddrinfo(3) for an example program that does
       this correctly.

SEE ALSO

       void(3type)