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<H1>copy_backward</H1>

<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "algorithms.gif" Alt=""   WIDTH = "194"  HEIGHT = "38" ></TD>
<TD Align=right><Img src = "function.gif" Alt=""   WIDTH = "194"  HEIGHT = "38" ></TD>
</TR>
<TR>
<TD Align=left VAlign=top><b>Category</b>: algorithms</TD>
<TD Align=right VAlign=top><b>Component type</b>: function</TD>
</TR>
</Table>

<h3>Prototype</h3>
<pre>
template &lt;class <A href="BidirectionalIterator.html">BidirectionalIterator</A>1, class <A href="BidirectionalIterator.html" tppabs="http://www.sgi.com/Technology/STL/BidirectionalIterator.shtml">BidirectionalIterator</A>2&gt;
BidirectionalIterator2 copy_backward(BidirectionalIterator1 first, 
                                     BidirectionalIterator1 last, 
                                     BidirectionalIterator2 result);
</pre>                   
<h3>Description</h3>
<tt>Copy_backward</tt> copies elements from the range <tt>[first, last)</tt> to the range
<tt>[result - (last - first), result)</tt> <A href="#1">[1]</A>.  That is, it performs the 
assignments <tt>*(result - 1) = *(last - 1)</tt>, <tt>*(result - 2) = *(last - 2)</tt>, 
and so on.   Generally, for every integer <tt>n</tt> from <tt>0</tt> to <tt>last - first</tt>,
<tt>copy_backward</tt> performs the assignment <tt>*(result - n - 1) = *(last - n - 1)</tt>.
Assignments are performed from the end of the input sequence to the 
beginning, <i>i.e.</i> in order of increasing <tt>n</tt>. <A href="#2">[2]</A>
<P>
The return value is <tt>result - (last - first)</tt>
<h3>Definition</h3>
Declared in <A href="algo.h">algo.h</A>.  The implementation is in <A href="algobase.h" tppabs="http://www.sgi.com/Technology/STL/algobase.h">algobase.h</A>.
<h3>Requirements on types</h3>
<UL>
<LI>
BidirectionalIterator1 and BidirectionalIterator2 are
   models of <A href="BidirectionalIterator.html">BidirectionalIterator</A>.
<LI>
BidirectionalIterator1's value type is convertible to
   BidirectionalIterator2's value type.
</UL>
<h3>Preconditions</h3>
<UL>
<LI>
<tt>[first, last)</tt> is a valid range.
<LI>
<tt>result</tt> is not an iterator within the range <tt>[first, last)</tt>.
<LI>
There is enough space to hold all of the elements being copied.
   More formally, the requirement is that 
   <tt>[result - (last - first), result)</tt> is a valid range.
</UL>
<h3>Complexity</h3>
Linear.  Exactly <tt>last - first</tt> assignments are performed.
<h3>Example</h3>
<pre>
<A href="Vector.html">vector</A>&lt;int&gt; V(15);
<A href="iota.html">iota</A>(V.begin(), V.end(), 1);
copy_backward(V.begin(), V.begin() + 10, V.begin() + 15);
</pre>
<h3>Notes</h3>
<P><A name="1">[1]</A>
<tt>Result</tt> is an iterator that points to the <i>end</i> of the output
range.  This is highly unusual: in all other STL algorithms that
denote an output range by a single iterator, that iterator points to
the beginning of the range.
<P><A name="2">[2]</A>
The order of assignments matters in the case where the input and
output ranges overlap:  <tt>copy_backward</tt> may not be used if <tt>result</tt> is
in the range <tt>[first, last)</tt>.  That is, it may not be used if the
end of the output range overlaps with the input range, but it may be
used if the beginning of the output range overlaps with the input
range; <tt><A href="copy.html">copy</A></tt> has opposite restrictions.
If the two ranges are completely nonoverlapping, of course, then
either algorithm may be used.
<h3>See also</h3>
<tt><A href="copy.html">copy</A></tt>, <tt><A href="copy_n.html" tppabs="http://www.sgi.com/Technology/STL/copy_n.shtml">copy_n</A></tt>

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