e6ccf0ce
 Hu Chunming
提交三方库
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<section id="array.intro">
<title>Introduction</title>
<using-namespace name="boost"/>
<using-class name="array"/>
<para>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).</para>
<para>As replacement for ordinary arrays, the STL provides class
<code><classname>std::vector</classname></code>. However,
<code><classname>std::vector<></classname></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.</para>
<para>In his book, <emphasis>Generic Programming and the
STL</emphasis>, Matthew H. Austern introduces a useful wrapper
class for ordinary arrays with static size, called
<code>block</code>. It is safer and has no worse performance than
ordinary arrays. In <emphasis>The C++ Programming
Language</emphasis>, 3rd edition, Bjarne Stroustrup introduces a
similar class, called <code>c_array</code>, which I (<ulink
url="http://www.josuttis.com">Nicolai Josuttis</ulink>) present
slightly modified in my book <emphasis>The C++ Standard Library -
A Tutorial and Reference</emphasis>, called
<code>carray</code>. This is the essence of these approaches
spiced with many feedback from <ulink
url="http://www.boost.org">boost</ulink>.</para>
<para>After considering different names, we decided to name this
class simply <code><classname>array</classname></code>.</para>
<para>Note that this class is suggested to be part of the next
Technical Report, which will extend the C++ Standard (see
<ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1548.htm">http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</ulink>).</para>
<para>Class <code><classname>array</classname></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:
<itemizedlist spacing="compact">
<listitem><simpara>No constructors are provided.</simpara></listitem>
<listitem><simpara>Elements may have an undetermined initial value (see <xref linkend="array.rationale"/>).</simpara></listitem>
<listitem><simpara><functionname>swap</functionname>() has no constant complexity.</simpara></listitem>
<listitem><simpara><methodname>size</methodname>() is always constant, based on the second template argument of the type.</simpara></listitem>
<listitem><simpara>The container provides no allocator support.</simpara></listitem>
</itemizedlist>
</para>
<para>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that:
<itemizedlist spacing="compact">
<listitem><simpara><methodname>front</methodname>() and <methodname>back</methodname>() are provided.</simpara></listitem>
<listitem><simpara><methodname>operator[]</methodname> and <methodname>at</methodname>() are provided.</simpara></listitem>
</itemizedlist>
</para>
</section>
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