std::deque swap() method

since C++17

// Non const version only
void swap( deque& other ) noexcept(/* see below */);

until C++17

// Non const version only
void swap( deque& other );

Exchanges the contents of the container with those of other. Does not invoke any move, copy, or swap operations on individual elements.

Invalidation

The past-the-end iterator is invalidated.
All iterators and references remain valid.

since C++11

If std::allocator_traits<allocator_type>::propagate_on_container_swap::value is true, then the allocators are exchanged using an unqualified call to non-member swap().
Otherwise, they are not swapped (and if get_allocator() != other.get_allocator(), the behavior is undefined

).

Parameters

• other - container to exchange the contents with

Return value

(none)

Complexity

Constant - O(1).

Exceptions

since C++17

noexcept(std::allocator_traits<Allocator>::is_always_equal::value)

until C++17

(none)

Example

Main.cpp

#include <iostream>
#include <deque>

template<class Os, class Co> Os& operator<<(Os& os, const Co& co) {
    os << "{";
    for (auto const& i : co) { os << ' ' << i; }
    return os << " } ";
}

int main()
{
    std::deque<int> a1{1, 2, 3}, a2{4, 5};

    auto it1 = std::next(a1.begin());
    auto it2 = std::next(a2.begin());

    int& ref1 = a1.front();
    int& ref2 = a2.front();

    std::cout << a1 << a2 << *it1 << ' ' << *it2 << ' ' << ref1 << ' ' << ref2 << '\n';
    a1.swap(a2);
    std::cout << a1 << a2 << *it1 << ' ' << *it2 << ' ' << ref1 << ' ' << ref2 << '\n';

    // Note that after swap the iterators and references stay associated with their
    // original elements, e.g. it1 that pointed to an element in 'a1' with value 2
    // still points to the same element, though this element was moved into 'a2'.
}

Possible output

{ 1 2 3 } { 4 5 } 2 5 1 4
{ 4 5 } { 1 2 3 } 2 5 1 4