set_intersection

     Algorithm

Summary

Basic set operation for sorted sequences.

Synopsis

Synopsis

#include <algorithm>

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

Description

The set_intersection algorithm constructs a sorted intersection of elements from the two ranges. It returns the end of the constructed range. When it finds an element present in both ranges, set_intersection always copies the element from the first range into result. This means that the result of set_intersection is guaranteed to be stable. The result of set_intersection is undefined if the result range overlaps with either of the original ranges.

set_intersection assumes that the ranges are sorted using the default comparision 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_intr.cpp
//
 #include <algorithm>
 #include <set>
 #include <iostream.h>
 int main()
 {
   //Initialize some sets
   int a1[10] = {1,3,5,7,9,11};
   int a3[4]  = {3,5,7,8};
   set<int, less<int> > odd(a1, a1+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_intersection
   cout << "The result of:" << endl << "{";
   copy(small.begin(),small.end(),
        ostream_iterator<int>(cout," "));
   cout << "} intersection {";
   copy(odd.begin(),odd.end(),
        ostream_iterator<int>(cout," "));
   cout << "} =" << endl << "{";
   set_intersection(small.begin(), small.end(),
                   odd.begin(), odd.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 } intersection {1 3 5 7 9 11 } =
{3 5 7 }

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>

instead of :

set<int>