How to find the intersection of two STL sets?
c++, stdset, stl-algorithm
Solution
You haven't provided an output iterator for `set_intersection`
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_intersection ( InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result );
Fix this by doing something like
...;
set<int> intersect;
set_intersection(s1.begin(), s1.end(), s2.begin(), s2.end(),
std::inserter(intersect, intersect.begin()));
You need a `std::insert` iterator since the set is as of now empty. We cannot use `std::back_inserter` or `std::front_inserter` since set doesn't support those operations.
Problem
I have been trying to find the intersection between two std::set in C++, but I keep getting an error. I created a small sample test for this ``` #include <iostream> #include <vector> #include <algorithm> #include <set> using namespace std; int main() { set<int> s1; set<int> s2; s1.insert(1); s1.insert(2); s1.insert(3); s1.insert(4); s2.insert(1); s2.insert(6); s2.insert(3); s2.insert(0); set_intersection(s1.begin(),s1.end(),s2.begin(),s2.end()); return 0; } ``` The latter program does not generate any output, but I expect to have a new set (let's call it `s3`) with the following values: ``` s3 = [ 1 , 3 ] ``` Instead, I'm getting the error: ``` test.cpp: In function ‘int main()’: test.cpp:19: error: no matching function for call to ‘set_intersection(std::_Rb_tree_const_iterator<int>, std::_Rb_tree_const_iterator<int>, std::_Rb_tree_const_iterator<int>, std::_Rb_tree_const_iterator<int>)’ ``` What I understand out of this error, is that there's no definition in `set_intersection` that accepts `Rb_tree_const_iterator<int>` as a parameter. Furthermore, I suppose the `std::set.begin()` method returns an object of such type, Is there a better way to find the intersection of two `std::set` in C++? Preferably a built-in function?