# Man Page set_difference.3

```
Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

```

## NAME

```     set_difference

- A basic set operation for constructing a  sorted  differ-
ence.

```

## SYNOPSIS

```     #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);

```

## DESCRIPTION

```     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  comparison operator less than (<), unless an alter-
native 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.

```

## COMPLEXITY

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

```

## EXAMPLE

```     //
// set_diff.cpp
//
#include <algorithm>
#include <set>
#include <iostream>
using namespace std;
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+0, a1+10), even(a2+0, 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,char>(cout," "));
cout << "} - {";
copy(even.begin(),even.end(),
ostream_iterator<int,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>(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 }

```

## WARNINGS

```     If your compiler does not support default  template  parame-
ters,  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> >

set<int>

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

```

```     includes,      set,       set_union,       set_intersection,
set_symmetric_difference

```