| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Rationale</title> |
| <link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> |
| <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> |
| <link rel="up" href="../align.html" title="Chapter 2. Boost.Align"> |
| <link rel="prev" href="../align.html" title="Chapter 2. Boost.Align"> |
| <link rel="next" href="tutorial.html" title="Tutorial"> |
| </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="../align.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="tutorial.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.rationale"></a><a class="link" href="rationale.html" title="Rationale">Rationale</a> |
| </h2></div></div></div> |
| <h4> |
| <a name="align.rationale.h0"></a> |
| <span class="phrase"><a name="align.rationale.dynamic_allocation"></a></span><a class="link" href="rationale.html#align.rationale.dynamic_allocation">Dynamic |
| allocation</a> |
| </h4> |
| <p> |
| C++11 added the ability to specify increased alignment (over-alignment) for |
| class types. Unfortunately, <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span> <span class="keyword">new</span></code> |
| allocation functions, <code class="computeroutput"><span class="keyword">new</span></code> expressions, |
| and the default allocator, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code>, |
| do not support dynamic memory allocation of over-aligned data. This library |
| provides allocation functions, allocators, allocator adaptors, and deleters, |
| that are alignment aware. |
| </p> |
| <div class="table"> |
| <a name="align.rationale.boost_align_solutions"></a><p class="title"><b>Table 2.2. Boost.Align solutions</b></p> |
| <div class="table-contents"><table class="table" summary="Boost.Align solutions"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Problem |
| </p> |
| </th> |
| <th> |
| <p> |
| Solution |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span> |
| <span class="keyword">new</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">no_throw_t</span><span class="special">&)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">aligned_alloc</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">)</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span> |
| <span class="keyword">delete</span><span class="special">(</span><span class="keyword">void</span><span class="special">*)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">aligned_free</span><span class="special">(</span><span class="keyword">void</span><span class="special">*)</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">aligned_allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Allocator</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">aligned_allocator_adaptor</span><span class="special"><</span><span class="identifier">Allocator</span><span class="special">></span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">default_delete</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">aligned_delete</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| </div> |
| <br class="table-break"><h4> |
| <a name="align.rationale.h1"></a> |
| <span class="phrase"><a name="align.rationale.alignment_functions"></a></span><a class="link" href="rationale.html#align.rationale.alignment_functions">Alignment |
| functions</a> |
| </h4> |
| <p> |
| C++11 provided <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">align</span></code> in the standard library to align a |
| pointer value. Unfortunately some C++ standard library implementations do not |
| support it yet (libstdc++ as far as gcc 4.8.0) and other standard library implementations |
| implement it incorrectly (dinkumware in msvc 11.0). This library provides it |
| for those implementations and also for C++03 compilers where it is equally |
| useful. |
| </p> |
| <h4> |
| <a name="align.rationale.h2"></a> |
| <span class="phrase"><a name="align.rationale.alignment_traits"></a></span><a class="link" href="rationale.html#align.rationale.alignment_traits">Alignment |
| traits</a> |
| </h4> |
| <p> |
| C++11 provided the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">alignment_of</span></code> trait in the standard library |
| to query the alignment requirement of a type. Unfortunately some C++ standard |
| library vendors do not implement it in an entirely standard conforming manner, |
| such as for array types (libc++ as far as clang 3.4). This library provides |
| it for those implementations and also for C++03 compilers where it is equally |
| useful. |
| </p> |
| <h4> |
| <a name="align.rationale.h3"></a> |
| <span class="phrase"><a name="align.rationale.alignment_testing"></a></span><a class="link" href="rationale.html#align.rationale.alignment_testing">Alignment |
| testing</a> |
| </h4> |
| <p> |
| This library provides a function to test the alignment of a pointer value. |
| It is generally useful in assertions to validate that memory is correctly aligned. |
| </p> |
| </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 Glen Fernandes<p> |
| Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost |
| Software License, Version 1.0</a>. |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="../align.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="tutorial.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
