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<P>&copy;Copyright 1996 Rogue Wave Software</P>
<H2>set_union</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_union</B> (InputIterator1 first1, InputIterator1 last1,
           InputIterator2 first2, InputIterator2 last2,
           OutputIterator result);
template &#60;class InputIterator1, class InputIterator2, 
          class OutputIterator, class Compare>
OutputIterator  
<B>set_union</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_union</B></I> algorithm constructs a sorted union of the elements from the two ranges.  It returns the end of the constructed range.  <B><I>set_union</B></I> is stable, that is, if an element is present in both ranges, the one from the first range is copied. The result of of <B><I>set_union</B></I> is undefined if the result range overlaps with either of the original ranges.  Note that <B><I>set_union</B></I> does not merge the two sorted sequences.  If an element is present in both sequences, only the element from the first sequence is copied to <SAMP>result</SAMP>.  (Use the <A HREF="mer_0626.htm"><B><I>merge</B></I></A> algorithm to create an ordered merge of two sorted sequences that contains all the elements from both sequences.)</P>
<P><B><I>set_union</B></I> assumes that the sequences are sorted using the default comparision operator less than (<SAMP>&#60;</SAMP>), unless an alternative comparison operator (<SAMP>comp</SAMP>) is provided. </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_unin.cpp
//
 #include &#60;algorithm>
 #include &#60;set>
 #include &#60;iostream.h>
 int main()
 {
   //Initialize some sets
   int a2[6]  = {2,4,6,8,10,12};
   int a3[4]  = {3,5,7,8};
   set&#60;int, less&#60;int> >  even(a2, a2+6), 
                        result, small(a3,a3+4);
   //Create an insert_iterator for result
   insert_iterator&#60;set&#60;int, less&#60;int> > > 
                 res_ins(result, result.begin());
   //Demonstrate set_union
   cout &#60;&#60; "The result of:" &#60;&#60; endl &#60;&#60; "{";
   copy(small.begin(),small.end(),
        ostream_iterator&#60;int>(cout," "));
   cout &#60;&#60; "} union {";
   copy(even.begin(),even.end(),
        ostream_iterator&#60;int>(cout," "));
   cout &#60;&#60; "} =" &#60;&#60; endl &#60;&#60; "{";
   <B>set_union</B>(small.begin(), small.end(),
            even.begin(), even.end(), res_ins);
   copy(result.begin(),result.end(),
        ostream_iterator&#60;int>(cout," "));
   cout &#60;&#60; "}" &#60;&#60; endl &#60;&#60; endl;
   return 0;
 }
Output :
The result of:
{3 5 7 8 } union {2 4 6 8 10 12 } =
{2 3 4 5 6 7 8 10 12 }
</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_9182.htm"><B><I>set_intersection</B></I></A>, <A HREF="set_0972.htm"><B><I>set_difference</B></I></A>, <A HREF="set_1735.htm"><B><I>set_symmetric_difference</B></I></A></P>
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