Apache C++ Standard Library Reference Guide

## set_difference()

Library:  Algorithms

`Function`

No Entries

### Summary

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

### Synopsis

```#include <algorithm>

namespace std {
template <class InputIterator1, class InputIterator2,
class OutputIterator>
OutputIterator
set_difference(InputIterator1 start1,
InputIterator1 finish1,
InputIterator2 start2,
InputIterator2 finish2,
OutputIterator result);
template <class InputIterator1, class InputIterator2,
class OutputIterator, class Compare>
OutputIterator
set_difference(InputIterator1 start1,
InputIterator1 finish1,
InputIterator2 start2,
InputIterator2 finish2,
OutputIterator result,
Compare comp);
}
```

### Description

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

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

### Complexity

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

### Example

```//
//  set_diff.cpp
//

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

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

// 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>,allocator<int> > all(a1+0, a1+10),
even(a2+0, a2+6), odd;

// Create an insert_iterator for odd.

insert_iterator<set <int, less<int>,allocator<int> > >
odd_ins(odd, odd.begin());

// Demonstrate set_difference.

cout << "The result of:" << endl << "{";
copy(all.begin(),all.end(),
ostream_iterator<int,char,char_traits<char> >
(cout," "));
cout << "} - {";
copy(even.begin(),even.end(),
ostream_iterator<int,char,char_traits<char> >
(cout," "));
cout << "} =" << endl << "{";
set_difference(all.begin(), all.end(), even.begin(),
even.end(), odd_ins);
copy(odd.begin(),odd.end(),
ostream_iterator<int,char,char_traits<char> >
(cout," "));
cout << "}" << endl << endl;

return 0;
}

Program 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 }

```

### Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.5.4