This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
stddef.h — standard type definitions
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.
header shall define the following macros:
- 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).
header shall define the following types:
- Signed integer type of the result of subtracting two
- 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
- Unsigned integer type of the result of the sizeof
The implementation shall support one or more programming environments in which
the widths of ptrdiff_t
, and wchar_t
greater than the width of type long
. The names of these programming
environments can be obtained using the confstr
() function or the
The following sections are informative.
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.
The System Interfaces volume of POSIX.1‐2008, confstr()
The Shell and Utilities volume of POSIX.1‐2008, getconf
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 Electrical 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