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

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C++
Containers library
std::vector
Member types
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
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

Run this code 
#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

See also

specializes the std::swap algorithm
(function template)
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