NAME
stddef —
standard type
definitions
SYNOPSIS
#include <stddef.h>
DESCRIPTION
The
<stddef.h> header defines the
following types and macros:
- ptrdiff_t, a signed integer type of
the result of subtracting two pointers;
- size_t, an unsigned integer type of
the result of the sizeof() operator;
- wchar_t, an integer type whose range
of values can represent distinct wide-character codes for all members of
the largest character set specified among the supported locales: the null
character has the code value 0 and each member of the character set has a
code value equal to its value when used as the lone character in an
integer character constant;
NULL
, which expands to an
implementation-defined null pointer constant; and
- offsetof(), a macro that expands to an
integer constant as described in
offsetof(3).
Some of the described types and macros may appear also in other headers.
SEE ALSO
offsetof(3),
stdlib(3),
unistd(3)
STANDARDS
As described here, the
<stddef.h>
header conforms to
ISO/IEC 9899:1999
(“ISO C99”) and
IEEE Std 1003.1-2001
(“POSIX.1”). Some of the types and macros conform to
earlier standards such as
ANSI X3.159-1989
(“ANSI C89”).
HISTORY
In the current form the
<stddef.h>
header was introduced in
NetBSD 0.8, the first
official release of
NetBSD. Some definitions such as
NULL
were first introduced already in the
<nsys/param.h> header of
Version 4 AT&T UNIX.