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std::vector<T,Allocator>::swap

void swap( vector& other );		(until C++17)
void swap( vector& other ) noexcept(/* see below */);		(since C++17) (until C++20)
constexpr void swap( vector& other ) noexcept(/* see below */);		(since C++20)

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

All iterators and references remain valid. The end() iterator is invalidated.

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).

(since C++11)

Parameters

other

container to exchange the contents with

Return value

(none).

Exceptions

(none).	(until C++17)
`noexcept` specification: `noexcept(std::allocator_traits<Allocator>::propagate_on_container_swap::value \|\| std::allocator_traits<Allocator>::is_always_equal::value)`	(since C++17)

Complexity

Constant.

Example

#include <iostream>
#include <vector>
 
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::vector<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'.
}

Output:

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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 341	C++98	the capacities of `std::vector` could not be swapped	they are also swapped