set_intersection of two sets

How to find the set intersection of two sets using STL algorithm?

Code:

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set<int> s1;
set<int> s2;

//& want to save it in set s i.e. s = s1^s2
set<int> s;
//i.e. s=?

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Check here for an example:

set_intersection - C++ Reference

It gives the number of the element in the given example.. I want to get the intersected set.

It gives the intersected set. The example just uses it only to display its size.

it gives the intersected set but the size of v doesn't change with the intersection size.

You're concerned that v may be too large? Then may I suggest using a back insert iterator to put elements of the intersected set at the end of the vector:

Code:

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  #include <iterator>
  vector<int> v;
  set_intersection (first, first+5, second, second+5, back_inserter(v));
  cout << "intersection has " << v.size() << " elements.\n";

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Output iterators usually start at the beginning, which will overwrite elements instead of letting the vector (or whatever) grow naturally. See back_insert_iterator - C++ Reference