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19 дек 2024, 19:11
19 дек 2024, 19:11
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Examples</title> <link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="../align.html" title="Chapter 3. Boost.Align"> <link rel="prev" href="rationale.html" title="Rationale"> <link rel="next" href="reference.html" title="Reference"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> <td align="center"><a href="../../../index.html">Home</a></td> <td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="rationale.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../align.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="reference.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="align.examples"></a><a class="link" href="examples.html" title="Examples">Examples</a> </h2></div></div></div> <h4> <a name="align.examples.h0"></a> <span class="phrase"><a name="align.examples.aligned_allocation"></a></span><a class="link" href="examples.html#align.examples.aligned_allocation">Aligned allocation</a> </h4> <p> To dynamically allocate storage with desired alignment, you can use the <code class="computeroutput"><span class="identifier">aligned_alloc</span></code> function: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span> <span class="identifier">storage</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_alloc</span><span class="special">(</span><span class="identifier">alignment</span><span class="special">,</span> <span class="identifier">size</span><span class="special">);</span></code> </li></ol></div> <p> To deallocate storage allocated with the <code class="computeroutput"><span class="identifier">aligned_alloc</span></code> function, use the <code class="computeroutput"><span class="identifier">aligned_free</span></code> function: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_free</span><span class="special">(</span><span class="identifier">storage</span><span class="special">);</span></code> </li></ol></div> <h4> <a name="align.examples.h1"></a> <span class="phrase"><a name="align.examples.aligned_allocator"></a></span><a class="link" href="examples.html#align.examples.aligned_allocator">Aligned allocator</a> </h4> <p> For C++ allocator aware code, you can use the <code class="computeroutput"><span class="identifier">aligned_allocator</span></code> class template for an allocator that respects over-alignment: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">int128_t</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_allocator</span><span class="special"><</span><span class="identifier">int128_t</span><span class="special">></span> <span class="special">></span> <span class="identifier">vector</span><span class="special">;</span></code> </li></ol></div> <p> This template allows specifying minimum alignment for all dynamic allocations: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_allocator</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="number">64</span><span class="special">></span> <span class="special">></span> <span class="identifier">vector</span><span class="special">;</span></code> </li></ol></div> <h4> <a name="align.examples.h2"></a> <span class="phrase"><a name="align.examples.aligned_allocator_adaptor"></a></span><a class="link" href="examples.html#align.examples.aligned_allocator_adaptor">Aligned allocator adaptor</a> </h4> <p> To turn an allocator into an allocator that respects over-alignment, you can use the <code class="computeroutput"><span class="identifier">aligned_allocator_adaptor</span></code> class template: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_allocator_adaptor</span><span class="special"><</span><span class="identifier">First</span><span class="special">></span> <span class="identifier">second</span><span class="special">(</span><span class="identifier">first</span><span class="special">);</span></code> </li></ol></div> <p> This template allows specifying minimum alignment for all dynamic allocations: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_allocator_adaptor</span><span class="special"><</span><span class="identifier">First</span><span class="special">,</span> <span class="number">64</span><span class="special">></span> <span class="identifier">second</span><span class="special">(</span><span class="identifier">first</span><span class="special">);</span></code> </li></ol></div> <h4> <a name="align.examples.h3"></a> <span class="phrase"><a name="align.examples.aligned_deleter"></a></span><a class="link" href="examples.html#align.examples.aligned_deleter">Aligned deleter</a> </h4> <p> For a deleter that can be paired with <code class="computeroutput"><span class="identifier">aligned_alloc</span></code>, you can use the <code class="computeroutput"><span class="identifier">aligned_delete</span></code> class: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">aligned_delete</span><span class="special">></span> <span class="identifier">pointer</span><span class="special">;</span></code> </li></ol></div> <h4> <a name="align.examples.h4"></a> <span class="phrase"><a name="align.examples.pointer_alignment"></a></span><a class="link" href="examples.html#align.examples.pointer_alignment">Pointer alignment</a> </h4> <p> To advance a pointer to the next address with the desired alignment: </p> <div class="orderedlist"><ol class="orderedlist" type="1"> <li class="listitem"> <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span> <span class="identifier">pointer</span> <span class="special">=</span> <span class="identifier">storage</span><span class="special">;</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">space</span> <span class="special">=</span> <span class="identifier">size</span><span class="special">;</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">align</span><span class="special">(</span><span class="number">64</span><span class="special">,</span> <span class="keyword">sizeof</span><span class="special">(</span><span class="keyword">double</span><span class="special">),</span> <span class="identifier">pointer</span><span class="special">,</span> <span class="identifier">space</span><span class="special">);</span></code> </li> </ol></div> <h4> <a name="align.examples.h5"></a> <span class="phrase"><a name="align.examples.querying_alignment"></a></span><a class="link" href="examples.html#align.examples.querying_alignment">Querying alignment</a> </h4> <p> To obtain the alignment of a given type at compie time, you can use: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">alignment_of</span><span class="special"><</span><span class="identifier">int128_t</span><span class="special">>::</span><span class="identifier">value</span></code> </li></ol></div> <p> If your compiler supports C++14 variable templates, you can also use: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">alignment_of_v</span><span class="special"><</span><span class="identifier">int128_t</span><span class="special">></span></code> </li></ol></div> <h4> <a name="align.examples.h6"></a> <span class="phrase"><a name="align.examples.hinting_alignment"></a></span><a class="link" href="examples.html#align.examples.hinting_alignment">Hinting alignment</a> </h4> <p> To inform the compiler about the alignment of a pointer, you can use: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">BOOST_ALIGN_ASSUME_ALIGNED</span><span class="special">(</span><span class="identifier">pointer</span><span class="special">,</span> <span class="number">64</span><span class="special">)</span></code> </li></ol></div> <h4> <a name="align.examples.h7"></a> <span class="phrase"><a name="align.examples.checking_alignment"></a></span><a class="link" href="examples.html#align.examples.checking_alignment">Checking alignment</a> </h4> <p> To check alignment of a pointer you can use the <code class="computeroutput"><span class="identifier">is_aligned</span></code> function: </p> <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> <code class="computeroutput"><span class="identifier">assert</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">alignment</span><span class="special">::</span><span class="identifier">is_aligned</span><span class="special">(</span><span class="identifier">pointer</span><span class="special">,</span> <span class="number">64</span><span class="special">));</span></code> </li></ol></div> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2014-2017 Glen Joseph Fernandes<p> Distributed under the Boost Software License, Version 1.0. </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="rationale.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../align.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="reference.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>