## set_symmetric_difference

    Algorithm

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Complexity
- Example
- Warnings
- See Also

### Summary

A basic set operation for constructing a sorted symmetric difference.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

### Synopsis

    #include <algorithm>
    template <class InputIterator1, class InputIterator2,
              class OutputIterator>
      OutputIterator
        set_symmetric_difference (InputIterator1 first1,
                                  InputIterator1 last1,
                                  InputIterator2 first2,
                                  InputIterator2 last2,
                                  OutputIterator result);
    template <class InputIterator1, class InputIterator2,
              class OutputIterator, class Compare>
      OutputIterator
        set_symmetric_difference (InputIterator1 first1,
                                  InputIterator1 last1,
                                  InputIterator2 first2,
                                  InputIterator2 last2,
                                  OutputIterator result,
                                  Compare comp);

### Description

set_symmetric_difference constructs a sorted symmetric difference of the elements from the two ranges. This means that the constructed range includes copies of the elements that are present in the range `[first1, last1)` (but not present in the range `[first2, last2)`) and copies of the elements that are present in the range `[first2, last2)` (but not in the range `[first1, last1)`). It returns the end of the constructed range.

For example, suppose we have two sets:

`1 2 3 4 5`

and

`3 4 5 6 7`

The set_symmetric_difference of these two sets is:

`1 2 6 7`

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

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

Use the set_symmetric_difference algorithm to return a result that includes elements that are present in the first set and not in the second.

### Complexity

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

### Example

    //
    // set_s_di.cpp
    //
    #include<algorithm>
    #include<set>
    #include <istream.h>
    using namespace std;

    int main()
     {

    //Initialize some sets
    int a1[] = {1,3,5,7,9,11};
    int a3[] = {3,5,7,8};
    set<int, less<int> > odd(a1+0,a1+6), result,
        small(a3+0,a3+4);
    //Create an insert_iterator for result
    insert_iterator<set<int, less<int> > >
        res_ins(result, result.begin());
    //Demonstrate set_symmetric_difference
    cout << "The symmetric difference of:" << endl << "{";
    copy(small.begin(),small.end(),
         ostream_iterator<int,char>(cout," "));
    cout << "} with {";
    copy(odd.begin(),odd.end(),
         ostream_iterator<int,char>(cout," "));
    cout << "} =" << endl << "{";
    set_symmetric_difference(small.begin(), small.end(),
                             odd.begin(), odd.end(), res_ins);
    copy(result.begin(),result.end(),
         ostream_iterator<int,char>(cout," "));
    cout << "}" << endl << endl;
    return 0;
     }

Program Output

    The symmetric difference of:
    {3 5 7 8 } with {1 3 5 7 9 11 } =
    {1 8 9 11 }

### Warnings

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

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

instead of:

`set<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

### See Also

includes, set, set_union,set_intersection, set_difference

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998