This algorithm helps you to retrieve all the elements contained in the first set (set1), but not in the second (set2).

Here’s the template:

templatevoid Diff(const T& set1, const T& set2, T& res) {    T temp;    typename T::const_iterator it = set1.begin();    if (&set1 == &set2)        return;    else {        while (it != set1.end()) {            if (set2.find(*it) == set2.end())  // element not found                temp.insert(*it);            ++i;        }    }    temp.swap(result);}