test for set and merge using STL

test_set_merge.cpp

    set<int> i1, i2, i3;
    int max = 10000;

    for(int i=1; i<max; i++) {
        i1.insert(i*5);
        i2.insert(i*10);
    }

    // set_union
    cout << "set_union --------" << endl;

    std::set_union(i1.begin(), i1.end(),
                   i2.begin(), i2.end(),
                   insert_iterator<set<int> >(i3, i3.begin() ));

    // caution: the following is not permitted because to try to write to readonly field.
    // std::set_union(i1.begin(), i1.end(), i2.begin(), i2.end(), i3.begin() );
    //                                                            ^^^^^^^^^^