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

NAME

 
set_difference
 
 - A basic set operation for constructing a sorted difference.
 
 
 

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 alternative 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 comparisons 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 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_symmetric_difference
 

Rogue Wave Software  —  Last change: 02 Apr 1998