stddef
—
standard type definitions
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.
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”).
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.