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<div><h2 class="title">
<a name="array"></a>Chapter 4. Boost.Array</h2></div>
<div><div class="author"><h3 class="author">
<span class="firstname">Nicolai</span> <span class="surname">Josuttis</span>
</h3></div></div>
<div><p class="copyright">Copyright © 2001-2004 Nicolai M. Josuttis</p></div>
<div><div class="legalnotice">
<a name="idm45555445531648"></a><p>Distributed under the Boost Software License, Version 1.0.
(See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at
<a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="array.html#array.intro">Introduction</a></span></dt>
<dt><span class="section"><a href="array/reference.html">Reference</a></span></dt>
<dd><dl><dt><span class="section"><a href="array/reference.html#header.boost.array_hpp">Header <boost/array.hpp></a></span></dt></dl></dd>
<dt><span class="section"><a href="array/rationale.html">Design Rationale</a></span></dt>
<dt><span class="section"><a href="array/more/info.html">For more information...</a></span></dt>
<dt><span class="section"><a href="array/ack.html">Acknowledgements</a></span></dt>
</dl>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="array.intro"></a>Introduction</h2></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://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1548.htm" target="_top">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</a>).</p>
<p>Update: <code class="computeroutput">std::array</code> is (as of C++11) part of the C++ standard.
The differences between <code class="computeroutput">boost::array</code> and <code class="computeroutput">std::array</code> are minimal.
If you are using C++11, you should consider using <code class="computeroutput">std::array</code> instead of <code class="computeroutput">boost::array</code>.
</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 compact" style="list-style-type: disc; ">
<li class="listitem">No constructors are provided.</li>
<li class="listitem">Elements may have an undetermined initial value (see <a class="xref" href="array/rationale.html" title="Design Rationale">the section called “Design Rationale”</a>).</li>
<li class="listitem">
<code class="computeroutput"><a class="link" href="boost/swap_idm45507162621920.html" title="Function swap">swap</a></code>() has no constant complexity.</li>
<li class="listitem">
<code class="computeroutput"><a class="link" href="boost/array.html#idm45507162983296-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 compact" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><a class="link" href="boost/array.html#idm45507162961280-bb">front</a></code>() and <code class="computeroutput"><a class="link" href="boost/array.html#idm45507162956640-bb">back</a></code>() are provided.</li>
<li class="listitem">
<code class="computeroutput"><a class="link" href="boost/array.html#idm45507162975808-bb">operator[]</a></code> and <code class="computeroutput"><a class="link" href="boost/array.html#idm45507162968544-bb">at</a></code>() are provided.</li>
</ul></div>
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