Home » C++ » c++ STL set difference

c++ STL set difference

Posted by: admin November 30, 2017 Leave a comment

Questions:

Does the C++ STL set data structure have a set difference operator?

Answers:

Yes there is, it is in <algorithm> and is called: std::set_difference. The usage is:

#include <algorithm>
#include <set>
#include <iterator>
// ...
std::set<int> s1, s2;
// Fill in s1 and s2 with values
std::set<int> result;
std::set_difference(s1.begin(), s1.end(), s2.begin(), s2.end(),
    std::inserter(result, result.end()));

In the end, the set result will contain the s1-s2.

Questions:
Answers:

Yes, there is a set_difference function in the algorithms header.

Edits:

FYI, the set data structure is able to efficiently use that algorithm, as stated in its documentation. The algorithm also works not just on sets but on any pair of iterators over sorted collections.

As others have mentioned, this is an external algorithm, not a method. Presumably that’s fine for your application.

Questions:
Answers:

Not an “operator” in the language sense, but there is the set_difference algorithm in the standard library:

http://www.cplusplus.com/reference/algorithm/set_difference.html

Of course, the other basic set operations are present too – (union etc), as suggested by the “See also” section at the end of the linked article.

Questions:
Answers:

The chosen answer is correct, but has some syntax errors.

Instead of

#include <algorithms>

use

#include <algorithm>

Instead of

std::insert_iterator(result, result.end()));

use

std::insert_iterator<set<int> >(result, result.end()));

Questions:
Answers:

Not as a method but there’s the external algorithm function set_difference

template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_difference(InputIterator1 first1, InputIterator1 last1,
                              InputIterator2 first2, InputIterator2 last2,
                              OutputIterator result);

http://www.sgi.com/tech/stl/set_difference.html

Questions:
Answers:

Apparently, it does.

SGI – set_difference

Questions:
Answers:

Once again, boost to the rescue:

#include <string>
#include <set>
#include <boost/range/algorithm/set_algorithm.hpp>

std::set<std::string> set0, set1, setDifference;
boost::set_difference(set0, set1, std::inserter(setDifference, setDifference.begin());

setDifference will contain set0-set1.

Questions:
Answers:

can we just use

 set_difference(set1.begin(), set1.end(), set2.begin(). set2,end(),std::back_inserter(result)).