swap-containers.cpp

// Swap containers

#include <algorithm>
#include <utility>
#include <vector>

int main()
{
  std::vector<int> v1 = { 1, 3, 5, 7 };
  std::vector<int> v2 = { 2, 4, 6, 8 };

  std::swap_ranges(std::begin(v1), std::end(v1), std::begin(v2));

  v1.swap(v2);

  using std::swap;
  swap(v1, v2);
}

// Swap the contents of two containers.
//
// On [9-10], we create two [`std::vector`](cpp/container/vector)s
// and initialise them with values.
//
// On [12], we swap the contents of the two `std::vector`s using the
// [`std::swap_ranges`](cpp/algorithm/swap_ranges) algorithm, which
// is given the beginning and end iterators of one range and the
// beginning iterator of a second range. This performs an
// element-by-element swap of their values (in this case, four swaps).
// The second range must have at least the number of elements in the
// first range. After this operation, iterators remain valid and point
// at the same container as they did previously.
//
// On [14], we use `std::vector`'s `swap` member function to swap the
// contents all in one shot. Alternatively, [16-17] perform the same
// operation with the [generic swap pattern](/patterns/swap-values.html).
// This approach is much faster than `std::swap_ranges`, as it simply
// swaps over the internal storage in constant time. It also does not
// require the containers to have the same size. However, after the
// operation, iterators will now point at the other container and
// past-the-end iterators are invalidated.