Retrieving Only Unique Elements from Two Sets

Here's the template:

template<class T>
void 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);
}