Apache C++ Standard Library Reference Guide

## set_symmetric_difference()

Library:  Algorithms

Function

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 }