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<P>&copy;Copyright 1996 Rogue Wave Software</P>
<H2>set_difference</H2>
<HR><PRE>     Algorithm</PRE><HR>
<A NAME="Summary"><H3>Summary</H3></A>
<P>Basic set operation for sorted sequences.</P>
<H3>Contents</H3>
<UL>
<A HREF="#Synopsis"><LI>Synopsis</LI></A>
<A HREF="#Description"><LI>Description</LI></A>
<A HREF="#Complexity"><LI>Complexity</LI></A>
<A HREF="#Example"><LI>Example</LI></A>
<A HREF="#Warning"><LI>Warning</LI></A>
<A HREF="#See Also"><LI>See Also</LI></A>
</UL>
<A NAME="Synopsis"><H3>Synopsis</H3></A>
<PRE>#include &#60;algorithm></PRE>
<PRE>
template &#60;class InputIterator1, class InputIterator2,
          class OutputIterator>
OutputIterator 
<B>set_difference</B> (InputIterator1 first1, InputIterator1 last1,
                InputIterator2 first2, InputIterator2 last2,
                OutputIterator result);
template &#60;class InputIterator1, class InputIterator2,
          class OutputIterator, class Compare>
OutputIterator 
<B>set_difference </B>(InputIterator1 first1, InputIterator1 last1,
                InputIterator2 first2, InputIterator2 last2,
                OutputIterator result, Compare comp);
</PRE>
<A NAME="Description"><H3>Description</H3></A>
<P>The <B><I>set_difference</B></I> algorithm constructs a sorted difference that includes copies of the elements that are present in the range <SAMP>[first1, last1)</SAMP> but are not present in the range <SAMP>[first2, last2)</SAMP>.  It returns the end of the constructed range.  </P>
<P>As an example, assume we have the following two sets:</P>
<PRE>1 2 3 4 5</PRE>
<PRE></PRE><P>and </P>
<PRE>3 4 5 6 7</PRE>
<PRE></PRE><P>The result of applying <B><I>set_difference</B></I> is the set:</P>
<PRE>1 2</PRE>
<PRE></PRE><P>The result of <B><I>set_difference</B></I> is undefined if the result range overlaps with either of the original ranges. </P>
<P><B><I>set_difference</B></I> assumes that the ranges are sorted using the default comparision operator less than (<SAMP>&#60;</SAMP>), unless an alternative comparison operator (<SAMP>comp</SAMP>) is provided. </P>
<P>Use the <B><I>set_symetric_difference</B></I> algorithm to return a result that contains all elements that are not in common between the two sets.</P>
<A NAME="Complexity"><H3>Complexity</H3></A>
<P>At most <SAMP>((last1 - first1) + (last2 - first2)) * 2 -1</SAMP>  comparisons are performed.</P>
<A NAME="Example"><H3>Example</H3></A>
<PRE>//
// set_diff.cpp
//
 #include &#60;algorithm>
 #include &#60;set>
 #include &#60;iostream.h></PRE><PRE> int main()
 {</PRE>
<PRE>   //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};</PRE><PRE>   set&#60;int, less&#60;int> > all(a1, a1+10), even(a2, a2+6), 
                        odd;</PRE>
<PRE>   //Create an insert_iterator for odd
   insert_iterator&#60;set&#60;int, less&#60;int> > >  
                 odd_ins(odd, odd.begin());
   //Demonstrate set_difference
   cout &#60;&#60; "The result of:" &#60;&#60; endl &#60;&#60; "{";
   copy(all.begin(),all.end(),
        ostream_iterator&#60;int>(cout," "));
   cout &#60;&#60; "} - {";
   copy(even.begin(),even.end(),
        ostream_iterator&#60;int>(cout," "));
   cout &#60;&#60; "} =" &#60;&#60; endl &#60;&#60; "{";
   <B>set_difference</B>(all.begin(), all.end(),
                  even.begin(), even.end(), odd_ins);
   copy(odd.begin(),odd.end(),
        ostream_iterator&#60;int>(cout," "));
   cout &#60;&#60; "}" &#60;&#60; endl &#60;&#60; endl;</PRE><PRE>   return 0;
 }</PRE>
<PRE>Output :
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>
<A NAME="Warning"><H3>Warning</H3></A>
<P>If your compiler does not support default template parameters, then you need to always supply the <SAMP>Compare</SAMP> template argument and the <SAMP>Allocator</SAMP> template argument. For instance, you will need to write :</P>
<P><SAMP>set&#60;int, less&#60;int> allocator></SAMP></P>
<P>instead of :</P>
<P><SAMP>set&#60;int></SAMP></P>
<A NAME="See Also"><H3>See Also</H3></A>
<P><A HREF="inc_3676.htm"><B><I>includes</B></I></A>, <A HREF="set_1649.htm"><B><I>set</B></I></A>, <A HREF="set_6462.htm"><B><I>set_union</B></I></A>,<A HREF="set_9182.htm"><B><I> set_intersection</B></I></A>, <A HREF="set_1735.htm"><B><I>set_symmetric_difference</B></I></A></P>
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