set_difference

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

The set_difference algorithm constructs a sorted difference that includes copies of the elements that are present in the range [first1, last1) but are not present in the range [first2, last2). It returns the end of the constructed range.

As an example, assume we have the following two sets:

1 2 3 4 5

and

3 4 5 6 7

The result of applying set_difference is the set:

1 2

The result of set_difference is undefined if the result range overlaps with either of the original ranges.

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

Use the set_symetric_difference algorithm to return a result that contains all elements that are not in common between the two sets.

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

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

 int main()
 {

   //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};

   set<int, less<int> > all(a1, a1+10), even(a2, a2+6), 
                        odd;

   //Create an insert_iterator for odd
   insert_iterator<set<int, less<int> > >  
                 odd_ins(odd, odd.begin());
   //Demonstrate set_difference
   cout << "The result of:" << endl << "{";
   copy(all.begin(),all.end(),
        ostream_iterator<int>(cout," "));
   cout << "} - {";
   copy(even.begin(),even.end(),
        ostream_iterator<int>(cout," "));
   cout << "} =" << endl << "{";
   set_difference(all.begin(), all.end(),
                  even.begin(), even.end(), odd_ins);
   copy(odd.begin(),odd.end(),
        ostream_iterator<int>(cout," "));
   cout << "}" << endl << endl;

   return 0;
 }

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 }

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_union, set_intersection, set_symmetric_difference