stddef.h(3)                POSIX Programmer's Manual               stddef.h(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       stddef.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.1-2017
       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
                 pointers.

       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
       environments can be obtained using the confstr() function or the
       getconf utility.

       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.1-2017, confstr()

       The Shell and Utilities volume of POSIX.1-2017, getconf

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          stddef.h(3)
