# std::swap(std::list)

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< cpp‎ | container‎ | list

Defined in header `<list>` |  |
template< class T, class Alloc > void swap( std::list<T, Alloc>& lhs, std::list<T, Alloc>& rhs ); |  | (until C++17)
template< class T, class Alloc > void swap( std::list<T, Alloc>& lhs, std::list<T, Alloc>& rhs ) noexcept(/* see below */); |  | (since C++17)

Specializes the std::swap algorithm for std::list. Swaps the contents of lhs and rhs. Calls lhs.swap(rhs).

### Parameters

lhs, rhs | - | containers whose contents to swap

### Return value

(none)

### Complexity

Constant.

### Exceptions

`noexcept` specification: noexcept(noexcept(lhs.swap(rhs))) | (since C++17)

### Notes

Although the overloads of std::swap for container adaptors are introduced in C++11, container adaptors can already be swapped by std::swap in C++98. Such calls to std::swap usually have linear time complexity, but better complexity may be provided.

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <list>

    int main()
    {
        std::list<int> alice{1, 2, 3};
        std::list<int> bob{7, 8, 9, 10};

        auto print = [](const int& n) { std::cout << ' ' << n; };

        // Print state before swap
        std::cout << "alice:";
        std::for_each(alice.begin(), alice.end(), print);
        std::cout << "\n" "bob  :";
        std::for_each(bob.begin(), bob.end(), print);
        std::cout << '\n';

        std::cout << "-- SWAP\n";
        std::swap(alice, bob);

        // Print state after swap
        std::cout << "alice:";
        std::for_each(alice.begin(), alice.end(), print);
        std::cout << "\n" "bob  :";
        std::for_each(bob.begin(), bob.end(), print);
        std::cout << '\n';
    }

Output:

    alice: 1 2 3
    bob  : 7 8 9 10
    -- SWAP
    alice: 7 8 9 10
    bob  : 1 2 3

### See also

swap | swaps the contents (public member function)

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