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stddef.h - standard type definitions
The <stddef.h> header shall define the following macros:
NULL Null pointer constant.
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:
Signed integer type of the result of subtracting two pointers.
Integer type whose range of values can represent distinct wide-
character codes for all members of the largest character set
specified among the locales supported by the compilation
environment: the null character has the code value 0 and each
member of the portable character set has a code value equal to
its value when used as the lone character in an integer
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
The following sections are informative.
<wchar.h> , <sys/types.h> , the System Interfaces volume of
IEEE Std 1003.1-2001, confstr(), the Shell and Utilities volume of
IEEE Std 1003.1-2001, getconf
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .