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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
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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.1-2008
       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)