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Computing › Stl › Algorithms › Set ›

set_difference

Processes a sorted range that contains all elements of a range that are not part of another
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Contents
  1. Definition
  2. Interface
  3. Description
  4. Return Value
  5. Complexity
  6. Page Comments

Definition

The set_difference() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.

Interface

#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 BinaryPredicate >
   OutputIterator set_difference(
      InputIterator1 first1, 
      InputIterator1 last1,
      InputIterator2 first2, 
      InputIterator2 last2, 
      OutputIterator result,
      BinaryPredicate comp
   );

Parameters:
Parameter Description
first1 An input iterator addressing the position of the first element in the first of two sorted source ranges to be united and sorted into a single range representing the difference of the two source ranges
last1 An input iterator addressing the position one past the last element in the first of two sorted source ranges to be united and sorted into a single range representing the difference of the two source ranges
first2 An input iterator addressing the position of the first element in second of two consecutive sorted source ranges to be united and sorted into a single range representing the difference of the two source ranges
last2 An input iterator addressing the position one past the last element in second of two consecutive sorted source ranges to be united and sorted into a single range representing the difference of the two source ranges
result An output iterator addressing the position of the first element in the destination range where the two source ranges are to be united into a single sorted range representing the difference of the two source ranges
comp User-defined predicate function object that defines the sense in which one element is greater than another. The binary predicate takes two arguments and should return true when the first element is less than the second element and false otherwise

Description

Set_difference creates a sorted range that is the set difference of the sorted ranges [first1, last1) and [first2, last2).
If an element is found m times in [first1, last1) and n times in [first2, last2), it will be copied to result exactly min(m-n, 0) times.

The first version compares objects using operator<, and the second compares objects using a function object comp.

Return Value

Returns an iterator on the element following the last of the build sequence.

Complexity

The complexity is linear; performs at most 2 * ((last1 - first1) + (last2 - first2)) - 1 comparisons.

References

Example:

Example - set_difference algorithm
Problem
This program illustrates the use of the STL set_difference() algorithm (default version) to find the values that are in a first vector of integers but not in a second vector of integers, and write them out to a third vector of integers.
Workings
#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
int main()
{
  int a1[] = {11, 12, 12, 12, 12, 13, 14, 15};
  vector<int> v1(a1, a1+8);
 
  cout <<"\nHere are the values in the vector v1:\n";
  for (vector<int>::size_type i=0; i<v1.size(); i++)
    cout <<v1.at(i)<<" ";
 
  int a2[] = {11, 12, 12, 13, 13, 16, 17, 18};
  vector<int> v2(a2, a2+8);
 
  cout <<"\nHere are the values in the vector v2:\n";
  for (vector<int>::size_type i=0; i<v2.size(); i++)
    cout <<v2.at(i)<<" ";
 
  int a3[] = {101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115};
  vector<int> v3(a3, a3+15);


  cout <<"\nHere are the values in the vector v3:\n";
  for (vector<int>::size_type i=0; i<v3.size(); i++)
    cout <<v3.at(i)<<" ";
 
   cout <<"\nNow we find the values that are in v1 but not in v2, "
         "and\nwrite them out to v3, starting at the beginning of v3."


  vector<int>::iterator p;
  p = set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
 
  cout <<"\nHere are the revised contents of v3:\n";
  for (vector<int>::size_type i=0; i<v3.size(); i++)
    cout <<v3.at(i)<<" ";
 
  cout <<"\nThe iterator returned by the algorithm is pointing at the value "<<*p<<".";
 
  return 0;
}
Solution
Output:

Here are the values in the vector v1:
11 12 12 12 12 13 14 15

Here are the values in the vector v2:
11 12 12 13 13 16 17 18

Here are the values in the vector v3:
101 102 103 104 105 106 107 108 109 110 111 112 113 114 115

Now we find the values that are in v1 but not in v2, and
write them out to v3, starting at the beginning of v3.

Here are the revised contents of v3:
12 12 14 15 105 106 107 108 109 110 111 112 113 114 115

The iterator returned by the algorithm is pointing at the value 105.
References

See Also

Last Modified: 2012-01-07 20:51:07     Page Rendered: 2012-05-22 03:51:25
 

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