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<TITLE>deque Operations</TITLE>
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<H2>7.2 deque Operations</H2>
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<P>A <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B> is declared the same way as a <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B>, and includes within the class the same type definitions as <B><I>vector</I></B>. The <SAMP>begin()</SAMP> and <SAMP>end()</SAMP> member functions return random access iterators, rather than the bidirectional iterators returned for <B><I><A HREF="../stdlibref/list.html">list</A></I></B>s. </P>
<P>An insertion  --  either <SAMP>insert()</SAMP>, <SAMP>push_front()</SAMP>, or <SAMP>push_back()</SAMP> --  can potentially invalidate all outstanding iterators and references to elements in the <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B>.  As with the <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B> datatype, this is a much more restrictive condition than insertions into a <B><I><A HREF="../stdlibref/list.html">list</A></I></B>.</P>
<P>If the underlying element type provides a destructor, the destructor is invoked when a value is erased from a <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B>.</P>
<P>Since the <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B> datatype provides random access iterators, all the generic algorithms that operate with <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B>s can also be used with <B><I>deque</I></B>s.</P>
<P>A <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B> holds elements in a single large block of memory. A <B><I><A HREF="../stdlibref/deque.html">deque</A></I></B>, on the other hand, uses a number of smaller blocks. This may be important on systems that restrict the size of memory blocks, as it permits a <B><I>deque</I></B> to hold many more elements than a <B><I>vector</I></B>.</P>
<P>As values are inserted, the index associated with any particular element in the collection changes. For example, if a value is inserted into position 3, the value formerly indexed by 3 is now found at index location 4; the value formerly at 4 is now found at index location 5, and so on.</P>

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