std::pair<T1,T2>::swap

 

C++

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Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI, type traits)      Library feature-test macros (C++20) Dynamic memory management Program utilities Error handling Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) launder (C++17) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20) is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) integer_sequence (C++14) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) forward (C++11) move (C++11) move_if_noexcept (C++11) as_const (C++17) to_underlying (C++23) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

std::pair

Member functions

pair::pair

pair::operator=

pair::swap (C++11)

Non-member functions

make_pair

operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

std::swap (C++11)

get (C++11)

Deduction guides(C++17)

Helper classes

tuple_size (C++11)

tuple_element (C++11)

basic_common_reference (C++23)

common_type (C++23)

 

	(1)
void swap( pair& other ) noexcept(/* see below */);			(since C++11) (until C++20)
constexpr void swap( pair& other ) noexcept(/* see below */);			(since C++20)
constexpr void swap( const pair& other ) noexcept(/* see below */);		(2)	(since C++23)

Swaps first with other.first and second with other.second, as if by using std::swap; swap(first, other.first); swap(second, other.second);.

If either selected swap function call is ill-formed or does not swap the value of the member, the behavior is undefined.	(until C++23)
1) The program is ill-formed if either std::is_swappable_v<T1> or std::is_swappable_v<T2> is not true. 2) The program is ill-formed if either std::is_swappable_v<const T1> or std::is_swappable_v<const T2> is not true. If either selected swap function call does not swap the value of the member, the behavior is undefined.	(since C++23)

Parameters

other

-

pair of values to swap

Return value

(none)

Exceptions

noexcept specification:   noexcept(      noexcept(swap(first, other.first)) &&      noexcept(swap(second, other.second)) ) In the expression above, the identifier swap is looked up in the same manner as the one used by the C++17 std::is_nothrow_swappable trait.	(until C++17)
1) noexcept specification:   noexcept(      std::is_nothrow_swappable_v<first_type> &&      std::is_nothrow_swappable_v<second_type> ) 2) noexcept specification:   noexcept(      std::is_nothrow_swappable_v<const first_type> &&      std::is_nothrow_swappable_v<const second_type> )	(since C++17)

Example

Run this code

#include <iostream>
#include <utility>
#include <string>
int main()
{
    std::pair<int, std::string> p1, p2;
    p1 = std::make_pair(10, "test");
    p2.swap(p1);
    std::cout << "(" << p2.first << ", " << p2.second << ")\n";
}

Output:

(10, test)

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 2456	C++11	the noexcept specification is ill-formed	made to work

See also

swap	swaps the values of two objects (function template)
swap (C++11)	swaps the contents of two tuples (public member function of std::tuple<Types...>)