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'\" et
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.TH stddef.h "0P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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.SH NAME
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stddef.h
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\(em standard type definitions
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.SH SYNOPSIS
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.LP
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.nf
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#include <stddef.h>
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.fi
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.SH DESCRIPTION
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The functionality described on this reference page is aligned with the
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ISO\ C standard. Any conflict between the requirements described here and the
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ISO\ C standard is unintentional. This volume of POSIX.1\(hy2008 defers to the ISO\ C standard.
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.P
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The
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.IR <stddef.h>
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header shall define the following macros:
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.IP NULL 10
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Null pointer constant.
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The macro shall expand to an integer constant expression with the
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value 0 cast to type
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.BR "void *" .
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.IP "offsetof(\fItype\fP, \fImember-designator\fP)" 10
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.br
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Integer constant expression of type
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.BR size_t ,
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the value of which is the offset in bytes to the structure member
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(\fImember-designator\fP), from the beginning of its structure
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(\fItype\fP).
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.P
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The
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.IR <stddef.h>
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header shall define the following types:
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.IP "\fBptrdiff_t\fP" 10
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Signed integer type of the result of subtracting two pointers.
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.IP "\fBwchar_t\fP" 10
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Integer type whose range of values can represent distinct codes for
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all members of the largest extended character set specified among the
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supported locales; the null character shall have the code value zero. Each
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member of the basic character set shall have a code value equal to its
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value when used as the lone character in an integer character constant
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if an implementation does not define _\|_STDC_MB_MIGHT_NEQ_WC_\|_.
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.IP "\fBsize_t\fP" 10
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Unsigned integer type of the result of the
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.IR sizeof
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operator.
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.P
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The implementation shall support one or more programming environments
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in which the widths of
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.BR ptrdiff_t ,
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.BR size_t ,
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and
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.BR wchar_t
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are no greater than the width of type
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.BR long .
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The names of these programming environments can be obtained using the
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\fIconfstr\fR()
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function or the
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.IR getconf
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utility.
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.LP
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.IR "The following sections are informative."
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.SH "APPLICATION USAGE"
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None.
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.SH RATIONALE
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The ISO\ C standard does not require the NULL macro to include the cast to type
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.BR "void *"
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and specifies that the NULL macro be implementation-defined. POSIX.1\(hy2008
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requires the cast and therefore need not be implementation-defined.
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.SH "FUTURE DIRECTIONS"
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None.
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.SH "SEE ALSO"
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.IR "\fB<sys_types.h>\fP",
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.IR "\fB<wchar.h>\fP"
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.P
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The System Interfaces volume of POSIX.1\(hy2008,
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.IR "\fIconfstr\fR\^(\|)"
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.P
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The Shell and Utilities volume of POSIX.1\(hy2008,
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.IR "\fIgetconf\fR\^"
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 7, Copyright (C) 2013 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group.
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(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
|
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is the referee document. The original Standard can be obtained online at
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http://www.unix.org/online.html .
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Any typographical or formatting errors that appear
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in this page are most likely
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to have been introduced during the conversion of the source files to
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man page format. To report such errors, see
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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