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<H2>set_difference()</H2>
<P><B>Library:</B>&nbsp;&nbsp;<A HREF="2-9.html">Algorithms</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Complexity</A></LI>
<LI><A HREF="#sec6">Example</A></LI>
<LI><A HREF="#sec7">See Also</A></LI>
<LI><A HREF="#sec8">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>A basic set operation (algorithm) for constructing a sorted difference</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;algorithm&gt;

namespace std {
  template &lt;class InputIterator1, class InputIterator2,
            class OutputIterator&gt;
  OutputIterator 
  set_difference(InputIterator1 start1,
                 InputIterator1 finish1,
                 InputIterator2 start2,
                 InputIterator2 finish2,
                 OutputIterator result);
  template &lt;class InputIterator1, class InputIterator2,
            class OutputIterator, class Compare&gt;
  OutputIterator 
  set_difference(InputIterator1 start1,
                 InputIterator1 finish1,
                 InputIterator2 start2,
                 InputIterator2 finish2,
                 OutputIterator result,
                 Compare comp);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <SAMP>set_difference()</SAMP> algorithm constructs a sorted difference that includes copies of the elements that are present in the range <SAMP>[start1, finish1)</SAMP> but are not present in the range <SAMP>[start2, finish2)</SAMP>. It returns the end of the constructed range. </P>
<P>As an example, assume we have the following two sets:</P>
<P><SAMP>1 2 3 4 5</SAMP></P>
<P>and </P>
<P><SAMP>3 4 5 6 7</SAMP></P>
<P>The result of applying <SAMP>set_difference()</SAMP> is the set:</P>
<P><SAMP>1 2</SAMP></P>
<P>The result of <SAMP>set_difference()</SAMP> is undefined if the result range overlaps with either of the original ranges. </P>
<P><SAMP>set_difference()</SAMP> assumes that the ranges are sorted using <SAMP>operator&lt;()</SAMP>, unless an alternative comparison function object (<SAMP>comp</SAMP>) is provided. </P>
<P>Use the <SAMP>set_symetric_difference()</SAMP> algorithm to obtain a result that contains all elements that are not in common between the two sets.</P>
<A NAME="sec5"><H3>Complexity</H3></A>
<P>At most <SAMP>((finish1 - start1) + (finish2 - start2)) * 2 -1</SAMP> comparisons are performed.</P>
<A NAME="sec6"><H3>Example</H3></A>

<UL><PRE>//
//  set_diff.cpp
//

#include &lt;algorithm&gt;
#include &lt;set&gt;
#include &lt;iostream&gt;

int main ()
{
#ifndef _RWSTD_NO_NAMESPACE
  using namespace std;
#endif


  // Initialize some sets.

  int a1[10] = {1,2,3,4,5,6,7,8,9,10};
  int a2[6]  = {2,4,6,8,10,12};

  set&lt;int, less&lt;int&gt;,allocator&lt;int&gt; &gt; all(a1+0, a1+10),
                                      even(a2+0, a2+6), odd;

  // Create an insert_iterator for odd.

  insert_iterator&lt;set &lt;int, less&lt;int&gt;,allocator&lt;int&gt; &gt; &gt; 
                 odd_ins(odd, odd.begin());

  // Demonstrate set_difference.

  cout &lt;&lt; "The result of:" &lt;&lt; endl &lt;&lt; "{";
  copy(all.begin(),all.end(),
       ostream_iterator&lt;int,char,char_traits&lt;char&gt; &gt;
                       (cout," "));
  cout &lt;&lt; "} - {";
  copy(even.begin(),even.end(),
       ostream_iterator&lt;int,char,char_traits&lt;char&gt; &gt;
                       (cout," "));
  cout &lt;&lt; "} =" &lt;&lt; endl &lt;&lt; "{";
  set_difference(all.begin(), all.end(), even.begin(),
                 even.end(), odd_ins);
  copy(odd.begin(),odd.end(),
       ostream_iterator&lt;int,char,char_traits&lt;char&gt; &gt;
                       (cout," "));
  cout &lt;&lt; "}" &lt;&lt; endl &lt;&lt; endl;

  return 0;
}


Program Output:
</PRE></UL>
<UL><PRE>The result of:
{1 2 3 4 5 6 7 8 9 10 } - {2 4 6 8 10 12 } =
{1 3 5 7 9 }

</PRE></UL>
<A NAME="sec7"><H3>See Also</H3></A>
<P><SAMP><A HREF="includes.html">includes()</A></SAMP>, <A HREF="iterators.html">Iterators</A>, <SAMP><A HREF="set-union.html">set_union()</A></SAMP>, <SAMP><A HREF="set-intersection.html">set_intersection()</A></SAMP>, <SAMP><A HREF="set-symmetric-difference.html">set_symmetric_difference()</A></SAMP></P>
<A NAME="sec8"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.5.4</I></P>

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