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XML Documentation</a>
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</h2></div></div></div>
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<div class="toc"><dl>
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<dt><span class="section"><a href="array.html#array.intro">Introduction</a></span></dt>
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<dt><span class="section"><a href="array.html#id772287">Reference</a></span></dt>
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<dt><span class="section"><a href="array.html#array.rationale">Design Rationale</a></span></dt>
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<dt><span class="section"><a href="array.html#array.more.info">For more information...</a></span></dt>
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<dt><span class="section"><a href="array.html#array.ack">Acknowledgements</a></span></dt>
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</dl></div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="array.intro"></a>Introduction</h3></div></div></div>
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<p>The C++ Standard Template Library STL as part of the C++
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Standard Library provides a framework for processing algorithms on
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different kind of containers. However, ordinary arrays don't
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provide the interface of STL containers (although, they provide
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the iterator interface of STL containers).</p>
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<p>As replacement for ordinary arrays, the STL provides class
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<code class="computeroutput">std::vector</code>. However,
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<code class="computeroutput">std::vector<></code> provides
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the semantics of dynamic arrays. Thus, it manages data to be able
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to change the number of elements. This results in some overhead in
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case only arrays with static size are needed.</p>
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<p>In his book, <span class="emphasis"><em>Generic Programming and the
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STL</em></span>, Matthew H. Austern introduces a useful wrapper
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class for ordinary arrays with static size, called
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<code class="computeroutput">block</code>. It is safer and has no worse performance than
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ordinary arrays. In <span class="emphasis"><em>The C++ Programming
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Language</em></span>, 3rd edition, Bjarne Stroustrup introduces a
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similar class, called <code class="computeroutput">c_array</code>, which I (<a href="http://www.josuttis.com" target="_top">Nicolai Josuttis</a>) present
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slightly modified in my book <span class="emphasis"><em>The C++ Standard Library -
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A Tutorial and Reference</em></span>, called
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<code class="computeroutput">carray</code>. This is the essence of these approaches
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spiced with many feedback from <a href="http://www.boost.org" target="_top">boost</a>.</p>
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<p>After considering different names, we decided to name this
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class simply <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">array</a></code>.</p>
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<p>Note that this class is suggested to be part of the next
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Technical Report, which will extend the C++ Standard (see
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1548.htm" target="_top">http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</a>).</p>
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<p>Class <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">array</a></code> fulfills most
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but not all of the requirements of "reversible containers" (see
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Section 23.1, [lib.container.requirements] of the C++
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Standard). The reasons array is not an reversible STL container is
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because:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc" compact>
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<li class="listitem">No constructors are provided.</li>
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<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>
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<li class="listitem">
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<code class="computeroutput"><a class="link" href="../boost/array.html#boost.array.swap">swap</a></code>() has no constant complexity.</li>
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<li class="listitem">
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<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>
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<li class="listitem">The container provides no allocator support.</li>
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</ul></div>
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<p>
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</p>
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<p>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc" compact>
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<li class="listitem">
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<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>
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<li class="listitem">
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<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>
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</ul></div>
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<p>
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</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="id772287"></a>Reference</h3></div></div></div>
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<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>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="header.boost.array_hpp"></a>Header <<a href="../../../../boost/array.hpp" target="_top">boost/array.hpp</a>></h4></div></div></div>
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<pre class="synopsis"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<span class="special">}</span></pre>
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</div>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="array.rationale"></a>Design Rationale</h3></div></div></div>
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<p>
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There was an important design tradeoff regarding the
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constructors: We could implement array as an "aggregate" (see
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Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would
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mean:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
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<p class="simpara">
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An array can be initialized with a
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brace-enclosing, comma-separated list of initializers for the
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elements of the container, written in increasing subscript
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order:
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</p>
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<pre class="programlisting">
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<code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { { 1, 2, 3 } };
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</pre>
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<p class="simpara">
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Note that if there are fewer elements in the
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initializer list, then each remaining element gets
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default-initialized (thus, it has a defined value).
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</p>
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</li></ul></div>
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<p>
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</p>
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<p>
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However, this approach has its drawbacks: <span class="bold"><strong>
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passing no initializer list means that the elements
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have an indetermined initial value
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</strong></span>, because the rule says
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that aggregates may have:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">No user-declared constructors.</li>
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<li class="listitem">No private or protected non-static data members.</li>
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<li class="listitem">No base classes.</li>
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<li class="listitem">No virtual functions.</li>
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</ul></div>
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<p>
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</p>
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<p>Nevertheless, The current implementation uses this approach.</p>
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<p>
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Note that for standard conforming compilers it is possible to
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use fewer braces (according to 8.5.1 (11) of the Standard). That is,
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you can initialize an array as follows:
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</p>
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<pre class="programlisting">
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<code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { 1, 2, 3 };
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</pre>
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<p>
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I'd appreciate any constructive feedback. <span class="bold"><strong>
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Please note: I don't have time to read all boost
|
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mails. Thus, to make sure that feedback arrives to me, please send
|
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me a copy of each mail regarding this class.
|
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</strong></span>
|
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</p>
|
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<p>
|
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The code is provided "as is" without expressed or implied
|
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warranty.
|
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</p>
|
|
</div>
|
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="array.more.info"></a>For more information...</h3></div></div></div>
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<p>
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To find more details about using ordinary arrays in C++ and
|
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the framework of the STL, see e.g.
|
|
|
|
</p>
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<div class="literallayout"><p><br>
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         The C++ Standard Library - A Tutorial and Reference<br>
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         by Nicolai M. Josuttis<br>
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         Addison Wesley Longman, 1999<br>
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         ISBN 0-201-37926-0<br>
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      </p></div>
|
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<p>
|
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</p>
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<p>
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<a href="http://www.josuttis.com/" target="_top">
|
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Home Page of Nicolai
|
|
Josuttis
|
|
</a>
|
|
</p>
|
|
</div>
|
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<div class="section">
|
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<div class="titlepage"><div><div><h3 class="title">
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<a name="array.ack"></a>Acknowledgements</h3></div></div></div>
|
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<p>Doug Gregor ported the documentation to the BoostBook format.</p>
|
|
</div>
|
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</div>
|
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2007 John Maddock, Joel de Guzman, Eric Niebler and Matias
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|
Capeletto<p>
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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>)
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</p>
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</div></td>
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</tr></table>
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<hr>
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