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128 lines
5.4 KiB
HTML
128 lines
5.4 KiB
HTML
4 years ago
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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) 1988-2018 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 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Restricted Pointers (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Restricted Pointers (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Restricted Pointers (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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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_002b_002b-Extensions.html#C_002b_002b-Extensions" rel="up" title="C++ Extensions">
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<link href="Vague-Linkage.html#Vague-Linkage" rel="next" title="Vague Linkage">
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<link href="C_002b_002b-Volatiles.html#C_002b_002b-Volatiles" rel="prev" title="C++ Volatiles">
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<style type="text/css">
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Restricted-Pointers"></a>
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<div class="header">
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<p>
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Next: <a href="Vague-Linkage.html#Vague-Linkage" accesskey="n" rel="next">Vague Linkage</a>, Previous: <a href="C_002b_002b-Volatiles.html#C_002b_002b-Volatiles" accesskey="p" rel="prev">C++ Volatiles</a>, Up: <a href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" accesskey="u" rel="up">C++ Extensions</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="Restricting-Pointer-Aliasing"></a>
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<h3 class="section">7.2 Restricting Pointer Aliasing</h3>
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<a name="index-restricted-pointers"></a>
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<a name="index-restricted-references"></a>
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<a name="index-restricted-this-pointer"></a>
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<p>As with the C front end, G++ understands the C99 feature of restricted pointers,
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specified with the <code>__restrict__</code>, or <code>__restrict</code> type
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qualifier. Because you cannot compile C++ by specifying the <samp>-std=c99</samp>
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language flag, <code>restrict</code> is not a keyword in C++.
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</p>
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<p>In addition to allowing restricted pointers, you can specify restricted
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references, which indicate that the reference is not aliased in the local
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context.
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</p>
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<div class="smallexample">
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<pre class="smallexample">void fn (int *__restrict__ rptr, int &__restrict__ rref)
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{
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/* <span class="roman">…</span> */
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}
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</pre></div>
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<p>In the body of <code>fn</code>, <var>rptr</var> points to an unaliased integer and
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<var>rref</var> refers to a (different) unaliased integer.
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</p>
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<p>You may also specify whether a member function’s <var>this</var> pointer is
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unaliased by using <code>__restrict__</code> as a member function qualifier.
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</p>
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<div class="smallexample">
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<pre class="smallexample">void T::fn () __restrict__
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{
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/* <span class="roman">…</span> */
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}
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</pre></div>
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<p>Within the body of <code>T::fn</code>, <var>this</var> has the effective
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definition <code>T *__restrict__ const this</code>. Notice that the
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interpretation of a <code>__restrict__</code> member function qualifier is
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different to that of <code>const</code> or <code>volatile</code> qualifier, in that it
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is applied to the pointer rather than the object. This is consistent with
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other compilers that implement restricted pointers.
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</p>
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<p>As with all outermost parameter qualifiers, <code>__restrict__</code> is
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ignored in function definition matching. This means you only need to
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specify <code>__restrict__</code> in a function definition, rather than
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in a function prototype as well.
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</p>
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</body>
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</html>
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