122 lines
5.2 KiB
HTML
122 lines
5.2 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using the GNU Compiler Collection (GCC): Arrays and pointers implementation</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC): Arrays and pointers implementation">
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<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Arrays and pointers implementation">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C-Implementation.html#C-Implementation" rel="up" title="C Implementation">
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<link href="Hints-implementation.html#Hints-implementation" rel="next" title="Hints implementation">
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<link href="Floating-point-implementation.html#Floating-point-implementation" rel="prev" title="Floating point implementation">
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Arrays-and-pointers-implementation"></a>
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<div class="header">
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<p>
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Next: <a href="Hints-implementation.html#Hints-implementation" accesskey="n" rel="next">Hints implementation</a>, Previous: <a href="Floating-point-implementation.html#Floating-point-implementation" accesskey="p" rel="prev">Floating point implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Arrays-and-Pointers"></a>
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<h3 class="section">4.7 Arrays and Pointers</h3>
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<ul>
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<li> <cite>The result of converting a pointer to an integer or
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vice versa (C90 6.3.4, C99 and C11 6.3.2.3).</cite>
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<p>A cast from pointer to integer discards most-significant bits if the
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pointer representation is larger than the integer type,
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sign-extends<a name="DOCF2" href="#FOOT2"><sup>2</sup></a>
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if the pointer representation is smaller than the integer type, otherwise
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the bits are unchanged.
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</p>
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<p>A cast from integer to pointer discards most-significant bits if the
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pointer representation is smaller than the integer type, extends according
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to the signedness of the integer type if the pointer representation
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is larger than the integer type, otherwise the bits are unchanged.
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</p>
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<p>When casting from pointer to integer and back again, the resulting
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pointer must reference the same object as the original pointer, otherwise
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the behavior is undefined. That is, one may not use integer arithmetic to
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avoid the undefined behavior of pointer arithmetic as proscribed in
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C99 and C11 6.5.6/8.
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</p>
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</li><li> <cite>The size of the result of subtracting two pointers to elements
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of the same array (C90 6.3.6, C99 and C11 6.5.6).</cite>
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<p>The value is as specified in the standard and the type is determined
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by the ABI.
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</p>
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</li></ul>
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<div class="footnote">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h3><a name="FOOT2" href="#DOCF2">(2)</a></h3>
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<p>Future versions of GCC may zero-extend, or use
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a target-defined <code>ptr_extend</code> pattern. Do not rely on sign extension.</p>
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</div>
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</body>
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</html>
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