oracular (3) NULL.3const.gz

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)