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128 lines
5.4 KiB
HTML
128 lines
5.4 KiB
HTML
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<html>
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any later version published by the Free Software Foundation; with the
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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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<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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</head>
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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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