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  27 <a name="document_to_test_formatting.array"></a><a class="link" href="array.html" title="Array Example Boostbook XML Documentation"> Array Example Boostbook
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  30 <div class="toc"><dl>
  31 <dt><span class="section"><a href="array.html#array.intro">Introduction</a></span></dt>
  32 <dt><span class="section"><a href="array.html#id772287">Reference</a></span></dt>
  33 <dt><span class="section"><a href="array.html#array.rationale">Design Rationale</a></span></dt>
  34 <dt><span class="section"><a href="array.html#array.more.info">For more information...</a></span></dt>
  35 <dt><span class="section"><a href="array.html#array.ack">Acknowledgements</a></span></dt>
  36 </dl></div>
  37 <div class="section">
  38 <div class="titlepage"><div><div><h3 class="title">
  39 <a name="array.intro"></a>Introduction</h3></div></div></div>
  40 <p>The C++ Standard Template Library STL as part of the C++
  41     Standard Library provides a framework for processing algorithms on
  42     different kind of containers. However, ordinary arrays don't
  43     provide the interface of STL containers (although, they provide
  44     the iterator interface of STL containers).</p>
  45 <p>As replacement for ordinary arrays, the STL provides class
  46     <code class="computeroutput">std::vector</code>.  However,
  47     <code class="computeroutput">std::vector&lt;&gt;</code> provides
  48     the semantics of dynamic arrays. Thus, it manages data to be able
  49     to change the number of elements. This results in some overhead in
  50     case only arrays with static size are needed.</p>
  51 <p>In his book, <span class="emphasis"><em>Generic Programming and the
  52     STL</em></span>, Matthew H. Austern introduces a useful wrapper
  53     class for ordinary arrays with static size, called
  54     <code class="computeroutput">block</code>.  It is safer and has no worse performance than
  55     ordinary arrays. In <span class="emphasis"><em>The C++ Programming
  56     Language</em></span>, 3rd edition, Bjarne Stroustrup introduces a
  57     similar class, called <code class="computeroutput">c_array</code>, which I (<a href="http://www.josuttis.com" target="_top">Nicolai Josuttis</a>) present
  58     slightly modified in my book <span class="emphasis"><em>The C++ Standard Library -
  59     A Tutorial and Reference</em></span>, called
  60     <code class="computeroutput">carray</code>. This is the essence of these approaches
  61     spiced with many feedback from <a href="http://www.boost.org" target="_top">boost</a>.</p>
  62 <p>After considering different names, we decided to name this
  63     class simply <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">array</a></code>.</p>
  64 <p>Note that this class is suggested to be part of the next
  65     Technical Report, which will extend the C++ Standard (see
  66     <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>
  67 <p>Class <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">array</a></code> fulfills most
  68     but not all of the requirements of "reversible containers" (see
  69     Section 23.1, [lib.container.requirements] of the C++
  70     Standard). The reasons array is not an reversible STL container is
  71     because:
  72       </p>
  73 <div class="itemizedlist"><ul class="itemizedlist" type="disc" compact>
  74 <li class="listitem">No constructors are provided.</li>
  75 <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 &#8220;Design Rationale&#8221;</a>).</li>
  76 <li class="listitem">
  77 <code class="computeroutput"><a class="link" href="../boost/array.html#boost.array.swap">swap</a></code>() has no constant complexity.</li>
  78 <li class="listitem">
  79 <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>
  80 <li class="listitem">The container provides no allocator support.</li>
  81 </ul></div>
  82 <p>
  83     </p>
  84 <p>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that:
  85       </p>
  86 <div class="itemizedlist"><ul class="itemizedlist" type="disc" compact>
  87 <li class="listitem">
  88 <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>
  89 <li class="listitem">
  90 <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>
  91 </ul></div>
  92 <p>
  93     </p>
  94 </div>
  95 <div class="section">
  96 <div class="titlepage"><div><div><h3 class="title">
  97 <a name="id772287"></a>Reference</h3></div></div></div>
  98 <div class="toc"><dl><dt><span class="section"><a href="array.html#header.boost.array_hpp">Header &lt;boost/array.hpp&gt;</a></span></dt></dl></div>
  99 <div class="section">
 100 <div class="titlepage"><div><div><h4 class="title">
 101 <a name="header.boost.array_hpp"></a>Header &lt;<a href="../../../../boost/array.hpp" target="_top">boost/array.hpp</a>&gt;</h4></div></div></div>
 102 <pre class="synopsis"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 103   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span> <span class="keyword">class</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special">;</span>
 104   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <a class="link" href="../boost/array.html" title="Class template array">array</a><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 105   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 106     <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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 107   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 108     <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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 109   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 110     <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_id331592"><span class="keyword">operator</span><span class="special">&lt;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 111   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 112     <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_id331679"><span class="keyword">operator</span><span class="special">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 113   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 114     <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_=_id331750"><span class="keyword">operator</span><span class="special">&lt;=</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 115   <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 116     <span class="keyword">bool</span> <a class="link" href="../boost/array.html#boost.array.operator_=_id332091"><span class="keyword">operator</span><span class="special">&gt;=</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</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">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
 117 <span class="special">}</span></pre>
 118 </div>
 119 </div>
 120 <div class="section">
 121 <div class="titlepage"><div><div><h3 class="title">
 122 <a name="array.rationale"></a>Design Rationale</h3></div></div></div>
 123 <p>
 124       There was an important design tradeoff regarding the
 125       constructors: We could implement array as an "aggregate" (see
 126       Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would
 127       mean:
 128       </p>
 129 <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
 130 <p class="simpara">
 131                An array can be initialized with a
 132                brace-enclosing, comma-separated list of initializers for the
 133                elements of the container, written in increasing subscript
 134                order:
 135             </p>
 136 <pre class="programlisting">
 137                <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code>&lt;int,4&gt; a = { { 1, 2, 3 } };
 138             </pre>
 139 <p class="simpara">
 140                Note that if there are fewer elements in the
 141                initializer list, then each remaining element gets
 142                default-initialized (thus, it has a defined value).
 143             </p>
 144 </li></ul></div>
 145 <p>
 146    </p>
 147 <p>
 148       However, this approach has its drawbacks: <span class="bold"><strong>
 149          passing no initializer list means that the elements
 150          have an indetermined initial value
 151       </strong></span>, because the rule says
 152       that aggregates may have:
 153       </p>
 154 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
 155 <li class="listitem">No user-declared constructors.</li>
 156 <li class="listitem">No private or protected non-static data members.</li>
 157 <li class="listitem">No base classes.</li>
 158 <li class="listitem">No virtual functions.</li>
 159 </ul></div>
 160 <p>
 161    </p>
 162 <p>Nevertheless, The current implementation uses this approach.</p>
 163 <p>
 164       Note that for standard conforming compilers it is possible to
 165       use fewer braces (according to 8.5.1 (11) of the Standard). That is,
 166       you can initialize an array as follows:
 167    </p>
 168 <pre class="programlisting">
 169       <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code>&lt;int,4&gt; a = { 1, 2, 3 };
 170    </pre>
 171 <p>
 172       I'd appreciate any constructive feedback. <span class="bold"><strong>
 173          Please note: I don't have time to read all boost
 174          mails. Thus, to make sure that feedback arrives to me, please send
 175          me a copy of each mail regarding this class.
 176       </strong></span>
 177    </p>
 178 <p>
 179       The code is provided "as is" without expressed or implied
 180       warranty.
 181    </p>
 182 </div>
 183 <div class="section">
 184 <div class="titlepage"><div><div><h3 class="title">
 185 <a name="array.more.info"></a>For more information...</h3></div></div></div>
 186 <p>
 187       To find more details about using ordinary arrays in C++ and
 188       the framework of the STL, see e.g.
 189
 190       </p>
 191 <div class="literallayout"><p><br>
 192 &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;The&#160;C++&#160;Standard&#160;Library&#160;-&#160;A&#160;Tutorial&#160;and&#160;Reference<br>
 193 &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;by&#160;Nicolai&#160;M.&#160;Josuttis<br>
 194 &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;Addison&#160;Wesley&#160;Longman,&#160;1999<br>
 195 &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;ISBN&#160;0-201-37926-0<br>
 196 &#160;&#160;&#160;&#160;&#160;&#160;</p></div>
 197 <p>
 198    </p>
 199 <p>
 200       <a href="http://www.josuttis.com/" target="_top">
 201          Home Page of Nicolai
 202          Josuttis
 203       </a>
 204    </p>
 205 </div>
 206 <div class="section">
 207 <div class="titlepage"><div><div><h3 class="title">
 208 <a name="array.ack"></a>Acknowledgements</h3></div></div></div>
 209 <p>Doug Gregor ported the documentation to the BoostBook format.</p>
 210 </div>
 211 </div>
 212 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 213 <td align="left"></td>
 214 <td align="right"><div class="copyright-footer">Copyright &#169; 2007 John Maddock, Joel de Guzman, Eric Niebler and Matias
 215       Capeletto<p>
 216         Distributed under the Boost Software License, Version 1.0. (See accompanying
 217         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>)
 218       </p>
 219 </div></td>
 220 </tr></table>
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