stddef.h(0P) POSIX Programmer's Manual stddef.h(0P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
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NAMEstddef.h — standard type definitions
SYNOPSIS
#include <stddef.h>
DESCRIPTION
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of POSIX.1‐2008
defers to the ISO C standard.
The <stddef.h> header shall define the following macros:
NULL Null pointer constant. The macro shall expand to an integer
constant expression with the value 0 cast to type void *.
offsetof(type, member-designator)
Integer constant expression of type size_t, the value of
which is the offset in bytes to the structure member (member-
designator), from the beginning of its structure (type).
The <stddef.h> header shall define the following types:
ptrdiff_t Signed integer type of the result of subtracting two point‐
ers.
wchar_t Integer type whose range of values can represent distinct
codes for all members of the largest extended character set
specified among the supported locales; the null character
shall have the code value zero. Each member of the basic
character set shall have a code value equal to its value when
used as the lone character in an integer character constant
if an implementation does not define
__STDC_MB_MIGHT_NEQ_WC__.
size_t Unsigned integer type of the result of the sizeof operator.
The implementation shall support one or more programming environments
in which the widths of ptrdiff_t, size_t, and wchar_t are no greater
than the width of type long. The names of these programming environ‐
ments can be obtained using the confstr() function or the getconf util‐
ity.
The following sections are informative.
APPLICATION USAGE
None.
RATIONALE
The ISO C standard does not require the NULL macro to include the cast
to type void * and specifies that the NULL macro be implementation-
defined. POSIX.1‐2008 requires the cast and therefore need not be
implementation-defined.
FUTURE DIRECTIONS
None.
SEE ALSO
<sys_types.h>, <wchar.h>
The System Interfaces volume of POSIX.1‐2008, confstr()
The Shell and Utilities volume of POSIX.1‐2008, getconf
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 stddef.h(0P)
