std::swap(std::pair)

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< cpp‎ | utility‎ | pair
 
 
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std::pair
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std::swap
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Defined in header <utility>
(1)
template< class T1, class T2 >

void swap( std::pair<T1,T2>& x, std::pair<T1,T2>& y )

    noexcept(/* see below */);
(since C++11)
(until C++20)
template< class T1, class T2 >

constexpr void swap( std::pair<T1,T2>& x, std::pair<T1,T2>& y )

    noexcept(/* see below */);
(since C++20)
template< class T1, class T2 >

constexpr void swap( const std::pair<T1,T2>& x, const std::pair<T1,T2>& y )

    noexcept(/* see below */);
(2) (since C++23)

Swaps the contents of x and y. Equivalent to x.swap(y).

1) This overload participates in overload resolution only if std::is_swappable_v<first_type> && std::is_swappable_v<second_type> is true.
2) This overload participates in overload resolution only if std::is_swappable_v<const first_type> && std::is_swappable_v<const second_type> is true.
(since C++17)

Parameters

x, y - pairs whose contents to swap

Return value

(none)

Exceptions

noexcept specification:  
noexcept(noexcept(x.swap(y)))

Example

#include <iostream>
#include <utility>
 
int main()
{
    auto p1 = std::make_pair(10, 3.14);
    auto p2 = std::pair(12, 1.23); // CTAD, since C++17
 
    auto print_p1_p2 = [&](auto msg) {
        std::cout << msg
                  << "p1 = {" << std::get<0>(p1)
                  << ", "     << std::get<1>(p1) << "}, "
                  << "p2 = {" << std::get<0>(p2)
                  << ", "     << std::get<1>(p2) << "}\n";
    };
 
    print_p1_p2("Before p1.swap(p2): ");
    p1.swap(p2);
    print_p1_p2("After  p1.swap(p2): ");
    std::swap(p1, p2);
    print_p1_p2("After swap(p1, p2): ");
}

Output:

Before p1.swap(p2): p1 = {10, 3.14}, p2 = {12, 1.23}
After  p1.swap(p2): p1 = {12, 1.23}, p2 = {10, 3.14}
After swap(p1, p2): p1 = {10, 3.14}, p2 = {12, 1.23}

See also

swaps the values of two objects
(function template)
specializes the std::swap algorithm
(function template)