set_union

     Algorithm

Basic set operation for sorted sequences.

Contents

• Synopsis
• Description
• Complexity
• Example
• Warning
• See Also

#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);

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 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 comparision operator less than (<), unless an alternative comparison operator (comp) is provided.

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

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

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>

instead of :

set<int>

includes, set, set_intersection, set_difference, set_symmetric_difference