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<TITLE>The deque Data Abstraction</TITLE>
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<H2>7.1 The deque Data Abstraction</H2>
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<P>The name <I>deque</I> is short for <I>double-ended queue</I>, and is pronounced like <I>deck</I>. Traditionally, the term is used to describe any data structure that permits both insertions and removals from either the front or the back of a collection. The <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B> container class permits this and much more. In fact, the capabilities of the <B><I>deque</I></B> data structure are almost a union of those provided by the <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B> and <B><I><A HREF="../stdlibref/list.html">list</A></I></B> classes.</P>
<P>Like a <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B>, the <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B> is an indexed collection. Values can be accessed by subscript, using the position within the collection as a key. This capability is not provided by the <B><I><A HREF="../stdlibref/list.html">list</A></I></B> class.</P>
<P>Like a <B><I><A HREF="../stdlibref/list.html">list</A></I></B>, however, values can be efficiently added either to the front or to the back of a <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B>. This capability is provided only in part by the vector class.</P>
<P>As with both the <B><I><A HREF="../stdlibref/list.html">list</A></I></B> and <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B> classes, insertions can be made into the middle of the sequence held by a <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B>. Such insertion operations are not as efficient as with a <B><I>list</I></B>, but slightly more efficient that they are in a <B><I>vector</I></B>.</P>
<P>In short, a <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B> can often be used in situations that require a <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B> and in situations that require a <B><I><A HREF="../stdlibref/list.html">list</A></I></B>. Often, using a <B><I>deque</I></B> in place of either a <B><I>vector</I></B> or a <B><I>list</I></B> results in faster programs. To determine which data structure should be used, you can refer to the set of questions described in <A HREF="4-2.html">Section&nbsp;4.2</A></P>
<A NAME="711"><H3>7.1.1 Include Files</H3></A>
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<P>The <SAMP>deque</SAMP> header file must appear in all programs that use the <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B> datatype:</P>

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#include &lt;deque&gt;
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