Apache C++ Standard Library Reference Guide

## set_symmetric_difference()

Library: Algorithms

    Function

- Local Index
- Summary
- Synopsis
- Description
- Complexity
- Example
- See Also
- Standards Conformance

### Local Index

No Entries

### Summary

A basic set operation (algorithm) for constructing a sorted symmetric difference

### Synopsis

    #include <algorithm>

    namespace std {
      template <class InputIterator1, class InputIterator2,
                class OutputIterator>
      OutputIterator
      set_symmetric_difference(InputIterator1 start1,
                               InputIterator1 finish1,
                               InputIterator2 start2,
                               InputIterator2 finish2,
                               OutputIterator result);

      template <class InputIterator1, class InputIterator2,
                class OutputIterator, class Compare>
      OutputIterator
      set_symmetric_difference(InputIterator1 start1,
                               InputIterator1 finish1,
                               InputIterator2 start2,
                               InputIterator2 finish2,
                               OutputIterator result,
                               Compare comp);
    }

### Description

The algorithm `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 `[start1, finish1)` (but not present in the range `[start2, finish2)`) and copies of the elements that are present in the range `[start2, finish2)` (but not in the range `[start1, finish1)`). 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 `operator<()`, unless an alternative comparison function object (`comp`) is provided.

Use the `set_symmetric_difference()` algorithm to obtain a result that includes elements that are present in the first set and not in the second.

### Complexity

At most `((finish1 - start1) + (finish2 - start2)) * 2 -1` comparisons are performed.

### Example

    //
    //  set_s_di.cpp
    //

    #include <algorithm>
    #include <set>
    #include <iostream>

    int main ()
    {
    #ifndef _RWSTD_NO_NAMESPACE
      using namespace std;
    #endif

      // Initialize some sets.

      int a1[] = {1,3,5,7,9,11};
      int a3[] = {3,5,7,8};
      set<int, less<int>,allocator<int>  > odd(a1+0, a1+6),
                                           result,
                                           smalll(a3+0, a3+4);

      // Create an insert_iterator for result.

      insert_iterator<set<int, less<int>,allocator<int> > >
                     res_ins(result, result.begin());

      // Demonstrate set_symmetric_difference.

      cout << "The symmetric difference of:" << endl << "{";
      copy(smalll.begin(),smalll.end(),
           ostream_iterator<int,char,char_traits<char> >
                           (cout," "));
      cout << "} with {";
      copy(odd.begin(),odd.end(),
           ostream_iterator<int,char,char_traits<char> >
                           (cout," "));
      cout << "} =" << endl << "{";
      set_symmetric_difference(smalll.begin(), smalll.end(),
                               odd.begin(), odd.end(), res_ins);
      copy(result.begin(),result.end(),
           ostream_iterator<int,char,char_traits<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 }

### See Also

`includes()`, Iterators, `set_union()`, `set_intersection()`, `set_difference()`

### Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.5.5