Standard C++	Library
 		 Copyright 1996, Rogue Wave Software, Inc.

 NAME

   set_union  - Basic set operation for sorted sequences.

 SYNOPSIS

   #include <algorithm>

   template <class InputIterator1, class	InputIterator2,	class OutputIterator>
   OutputIterator
   set_union (InputIterator1 first1, InputIterator1 last1,
 	    InputIterator2 first2, InputIterator2 last2,
 	    OutputIterator result);

   template <class InputIterator1, class	InputIterator2,
 	   class OutputIterator, class Compare>
   OutputIterator
   set_union (InputIterator1 first1, InputIterator1 last1,
 	    InputIterator2 first2, InputIterator2 last2,
 	    OutputIterator result, Compare comp);

 DESCRIPTION

   The set_union	algorithm constructs a sorted union of the elements
   from the two ranges.  It returns the end of the constructed range.
   set_union is stable, that is, if an element is present in both
   ranges, the	one from the first	range is copied. The result of
   set_union is undefined if the result range	overlaps with either
   of	the original ranges.  Note that	set_union 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
   result. (Use the merge algorithm to create an	ordered	merge of two
   sorted sequences that contains	all the	elements from both
   sequences.)

   set_union assumes that the sequences are sorted using	the default
   comparison operator less	than (<), unless an alternative
   comparison operator (comp) is provided.

 COMPLEXITY

   At most ((last1 - first1) + (last2 - first2))	* 2 -1	comparisons
   are	performed.

 EXAMPLE

   //
   // set_unin.cpp
   //
    #include <algorithm>
    #include <set>
    #include <iostream.h>

   int main()
    {

      //Initialize some sets
     int	a2[6]  = {2,4,6,8,10,12};
     int	a3[4]  = {3,5,7,8};
     set<int, less<int> >  even(a2, a2+6),
 			 result, small(a3,a3+4);

      //Create an insert_iterator for result
     insert_iterator<set<int, less<int> > >
 		  res_ins(result, result.begin());

      //Demonstrate set_union
     cout << "The result	of:" <<	endl <<	"{";
     copy(small.begin(),small.end(),
 	 ostream_iterator<int,char>(cout," "));
     cout << "} union {";
     copy(even.begin(),even.end(),
 	 ostream_iterator<int,char>(cout," "));
     cout << "} =" << endl << "{";
      set_union(small.begin(), small.end(),
 	     even.begin(), even.end(), res_ins);
     copy(result.begin(),result.end(),
 	 ostream_iterator<int,char>(cout," "));
     cout << "}"	<< endl	<< 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 }

 WARNING

   If your compiler does	not support default template parameters, then
   you need to always supply	the Compare template argument and the
   Allocator	template	argument. For instance,	you will need
   to write :

   set<int, less<int>, allocator<int> >

   instead of :

   set<int>

 SEE ALSO

   includes, set, set_intersection, set_difference, set_symmetric_difference

 STANDARDS CONFORMANCE
   ANSI X3J16/ISO WG21 Joint C++	Committee