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| <div class="toc"><dl> |
| <dt><span class="section"><a href="array.html#array.intro">Introduction</a></span></dt> |
| <dt><span class="section"><a href="array.html#id772287">Reference</a></span></dt> |
| <dt><span class="section"><a href="array.html#array.rationale">Design Rationale</a></span></dt> |
| <dt><span class="section"><a href="array.html#array.more.info">For more information...</a></span></dt> |
| <dt><span class="section"><a href="array.html#array.ack">Acknowledgements</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="array.intro"></a>Introduction</h3></div></div></div> |
| <p>The C++ Standard Template Library STL as part of the C++ |
| Standard Library provides a framework for processing algorithms on |
| different kind of containers. However, ordinary arrays don't |
| provide the interface of STL containers (although, they provide |
| the iterator interface of STL containers).</p> |
| <p>As replacement for ordinary arrays, the STL provides class |
| <code class="computeroutput">std::vector</code>. However, |
| <code class="computeroutput">std::vector<></code> provides |
| the semantics of dynamic arrays. Thus, it manages data to be able |
| to change the number of elements. This results in some overhead in |
| case only arrays with static size are needed.</p> |
| <p>In his book, <span class="emphasis"><em>Generic Programming and the |
| STL</em></span>, Matthew H. Austern introduces a useful wrapper |
| class for ordinary arrays with static size, called |
| <code class="computeroutput">block</code>. It is safer and has no worse performance than |
| ordinary arrays. In <span class="emphasis"><em>The C++ Programming |
| Language</em></span>, 3rd edition, Bjarne Stroustrup introduces a |
| similar class, called <code class="computeroutput">c_array</code>, which I (<a href="http://www.josuttis.com" target="_top">Nicolai Josuttis</a>) present |
| slightly modified in my book <span class="emphasis"><em>The C++ Standard Library - |
| A Tutorial and Reference</em></span>, called |
| <code class="computeroutput">carray</code>. This is the essence of these approaches |
| spiced with many feedback from <a href="http://www.boost.org" target="_top">boost</a>.</p> |
| <p>After considering different names, we decided to name this |
| class simply <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">array</a></code>.</p> |
| <p>Note that this class is suggested to be part of the next |
| Technical Report, which will extend the C++ Standard (see |
| <a href="http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm" target="_top">http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</a>).</p> |
| <p>Class <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">array</a></code> fulfills most |
| but not all of the requirements of "reversible containers" (see |
| Section 23.1, [lib.container.requirements] of the C++ |
| Standard). The reasons array is not an reversible STL container is |
| because: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc" compact> |
| <li class="listitem">No constructors are provided.</li> |
| <li class="listitem">Elements may have an undetermined initial value (see <a class="xref" href="array.html#array.rationale" title="Design Rationale">the section called “Design Rationale”</a>).</li> |
| <li class="listitem"> |
| <code class="computeroutput"><a class="link" href="../boost/array.html#boost.array.swap">swap</a></code>() has no constant complexity.</li> |
| <li class="listitem"> |
| <code class="computeroutput"><a class="link" href="../boost/array.html#id330848-bb">size</a></code>() is always constant, based on the second template argument of the type.</li> |
| <li class="listitem">The container provides no allocator support.</li> |
| </ul></div> |
| <p> |
| </p> |
| <p>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc" compact> |
| <li class="listitem"> |
| <code class="computeroutput"><a class="link" href="../boost/array.html#id331056-bb">front</a></code>() and <code class="computeroutput"><a class="link" href="../boost/array.html#id331110-bb">back</a></code>() are provided.</li> |
| <li class="listitem"> |
| <code class="computeroutput"><a class="link" href="../boost/array.html#id330919-bb">operator[]</a></code> and <code class="computeroutput"><a class="link" href="../boost/array.html#id330982-bb">at</a></code>() are provided.</li> |
| </ul></div> |
| <p> |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id772287"></a>Reference</h3></div></div></div> |
| <div class="toc"><dl><dt><span class="section"><a href="array.html#header.boost.array_hpp">Header <boost/array.hpp></a></span></dt></dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="header.boost.array_hpp"></a>Header <<a href="../../../../boost/array.hpp" target="_top">boost/array.hpp</a>></h4></div></div></div> |
| <pre class="synopsis"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> <span class="keyword">class</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> <span class="keyword">void</span> <a class="link" href="../boost/array.html#boost.array.swap"><span class="identifier">swap</span></a><span class="special">(</span><a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> |
| <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator=="><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> |
| <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator!="><span class="keyword">operator</span><span class="special">!=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> |
| <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_id331592"><span class="keyword">operator</span><span class="special"><</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> |
| <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_id331679"><span class="keyword">operator</span><span class="special">></span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> |
| <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_=_id331750"><span class="keyword">operator</span><span class="special"><=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> N<span class="special">></span> |
| <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_=_id332091"><span class="keyword">operator</span><span class="special">>=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span><span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| </div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="array.rationale"></a>Design Rationale</h3></div></div></div> |
| <p> |
| There was an important design tradeoff regarding the |
| constructors: We could implement array as an "aggregate" (see |
| Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would |
| mean: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| <p class="simpara"> |
| An array can be initialized with a |
| brace-enclosing, comma-separated list of initializers for the |
| elements of the container, written in increasing subscript |
| order: |
| </p> |
| <pre class="programlisting"> |
| <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { { 1, 2, 3 } }; |
| </pre> |
| <p class="simpara"> |
| Note that if there are fewer elements in the |
| initializer list, then each remaining element gets |
| default-initialized (thus, it has a defined value). |
| </p> |
| </li></ul></div> |
| <p> |
| </p> |
| <p> |
| However, this approach has its drawbacks: <span class="bold"><strong> |
| passing no initializer list means that the elements |
| have an indetermined initial value |
| </strong></span>, because the rule says |
| that aggregates may have: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem">No user-declared constructors.</li> |
| <li class="listitem">No private or protected non-static data members.</li> |
| <li class="listitem">No base classes.</li> |
| <li class="listitem">No virtual functions.</li> |
| </ul></div> |
| <p> |
| </p> |
| <p>Nevertheless, The current implementation uses this approach.</p> |
| <p> |
| Note that for standard conforming compilers it is possible to |
| use fewer braces (according to 8.5.1 (11) of the Standard). That is, |
| you can initialize an array as follows: |
| </p> |
| <pre class="programlisting"> |
| <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { 1, 2, 3 }; |
| </pre> |
| <p> |
| I'd appreciate any constructive feedback. <span class="bold"><strong> |
| Please note: I don't have time to read all boost |
| mails. Thus, to make sure that feedback arrives to me, please send |
| me a copy of each mail regarding this class. |
| </strong></span> |
| </p> |
| <p> |
| The code is provided "as is" without expressed or implied |
| warranty. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="array.more.info"></a>For more information...</h3></div></div></div> |
| <p> |
| To find more details about using ordinary arrays in C++ and |
| the framework of the STL, see e.g. |
| |
| </p> |
| <div class="literallayout"><p><br> |
|          The C++ Standard Library - A Tutorial and Reference<br> |
|          by Nicolai M. Josuttis<br> |
|          Addison Wesley Longman, 1999<br> |
|          ISBN 0-201-37926-0<br> |
|       </p></div> |
| <p> |
| </p> |
| <p> |
| <a href="http://www.josuttis.com/" target="_top"> |
| Home Page of Nicolai |
| Josuttis |
| </a> |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="array.ack"></a>Acknowledgements</h3></div></div></div> |
| <p>Doug Gregor ported the documentation to the BoostBook format.</p> |
| </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 © 2007 John Maddock, Joel de Guzman, Eric Niebler and Matias |
| Capeletto<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
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