Sorting zipped (locked) containers in C++ using boost or the STL

Here's a working example based on the range-v3 Library that has been proposed for Standardization

#include <range/v3/all.hpp>
#include <iostream>

using namespace ranges;

int main() 
{
    std::vector<int> a1{15, 7, 3,  5};
    std::vector<int> a2{ 1, 2, 6, 21};
    sort(view::zip(a1, a2), std::less<>{}, &std::pair<int, int>::first); 
    std::cout << view::all(a1) << '\n';
    std::cout << view::all(a2) << '\n';
}

Live Example (requires recent compiler with good C++14 support, not VS 2015).

For the two container case, here's a version that compiles on gcc 4.4.6, based on the paper referred to above. In later versions of gcc, you can swap out boost::tuple for std::tuple

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>

# include <boost/iterator/iterator_facade.hpp>
# include <boost/tuple/tuple.hpp> 

using namespace std;

template <class T, class T2>
struct helper_type {
  typedef boost::tuple<typename iterator_traits<T>::value_type, typename iterator_traits<T2>::value_type> value_type;
  typedef boost::tuple<typename iterator_traits<T>::value_type&, typename iterator_traits<T2>::value_type&> ref_type;
};

template <typename T1, typename T2>
class dual_iterator : public boost::iterator_facade<dual_iterator<T1, T2>,
                                                    typename helper_type<T1, T2>::value_type,
                                                    boost::random_access_traversal_tag,
                                                    typename helper_type<T1, T2>::ref_type> {
public:
   explicit dual_iterator(T1 iter1, T2 iter2) : mIter1(iter1), mIter2(iter2) {}
   typedef typename iterator_traits<T1>::difference_type difference_type;
private:
   void increment() { ++mIter1; ++mIter2; }
   void decrement() { --mIter1; --mIter2; }
   bool equal(dual_iterator const& other) const { return mIter1 == other.mIter1; }
   typename helper_type<T1, T2>::ref_type dereference() const { return (typename helper_type<T1, T2>::ref_type(*mIter1, *mIter2)); }
   difference_type distance_to(dual_iterator const& other) const { return other.mIter1 - mIter1; }
   void advance(difference_type n) { mIter1 += n; mIter2 += n; }

   T1 mIter1;
   T2 mIter2;
   friend class boost::iterator_core_access;
};

template <typename T1, typename T2>
dual_iterator<T1, T2> make_iter(T1 t1, T2 t2) { return dual_iterator<T1, T2>(t1, t2); }

template <class T1, class T2> struct iter_comp {
  typedef typename helper_type<T1, T2>::value_type T;
  bool operator()(const T& t1, const T& t2) { return get<0>(t1) < get<0>(t2); }
};

template <class T1, class T2> iter_comp<T1, T2> make_comp(T1 t1, T2 t2) { return iter_comp<T1, T2>(); }

template<class T> void print(T& items) {
  copy(items.begin(), items.end(), ostream_iterator<typename T::value_type>(cout, " ")); cout << endl;
}

int main() {
  vector<double> nums1 = {3, 2, 1, 0};
  vector<char> nums2 = {'D','C', 'B', 'A'};
  sort(make_iter(nums1.begin(), nums2.begin()), 
       make_iter(nums1.end(), nums2.end()), 
       make_comp(nums1.begin(), nums2.begin()));
  print(nums1);
  print(nums2);
}