std::swap

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Algorithm library

Constrained algorithms and algorithms on ranges(C++20)

Constrained algorithms, e.g.ranges::copy,ranges::sort, ...

Execution policies(C++17)

is_execution_policy

(C++17)

execution::seqexecution::parexecution::par_unseqexecution::unseq

(C++17) (C++17)(C++17)(C++20)

execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced

(C++17)(C++17)(C++17)(C++20)

Non-modifying sequence operations

(C++17)

all_ofany_ofnone_of (C++11) (C++11)(C++11)
countcount_if
mismatch
equal

findfind_iffind_if_not (C++11)
find_end
find_first_of
adjacent_find
search
search_n

Modifying sequence operations

Copy operations

copycopy_if (C++11)
copy_backward

copy_n (C++11)
move (C++11)
move_backward (C++11)

Swap operations

swap
iter_swap

swap_ranges

Transformation operations

replacereplace_if
transform

replace_copyreplace_copy_if

Generation operations

fill
fill_n

generate
generate_n

Removing operations

removeremove_if
unique

remove_copyremove_copy_if
unique_copy

Order-changing operations

reverse
reverse_copy
rotate
rotate_copy

random_shuffleshuffle (until C++17)(C++11)
shift_leftshift_right (C++20)(C++20)

Sampling operations

sample

(C++17)

Sorting and related operations

Partitioning operations

partition
partition_copy (C++11)
stable_partition

is_partitioned (C++11)
partition_point (C++11)

Sorting operations

sort
stable_sort
partial_sort
partial_sort_copy

is_sorted (C++11)
is_sorted_until (C++11)
nth_element

Binary search operations
(on partitioned ranges)

lower_bound
upper_bound

equal_range
binary_search

Set operations (on sorted ranges)

includes
set_union
set_intersection

set_difference
set_symmetric_difference

Merge operations (on sorted ranges)

merge

inplace_merge

Heap operations

push_heap
pop_heap
make_heap

sort_heap
is_heap (C++11)
is_heap_until (C++11)

Minimum/maximum operations

max
min
minmax (C++11)
clamp (C++17)

max_element
min_element
minmax_element (C++11)

Lexicographical comparison operations

lexicographical_compare

lexicographical_compare_three_way

(C++20)

Permutation operations

next_permutation
prev_permutation

is_permutation (C++11)

iota (C++11)
inner_product
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accumulate
reduce (C++17)
transform_reduce (C++17)

partial_sum
inclusive_scan (C++17)
exclusive_scan (C++17)

transform_inclusive_scan (C++17)
transform_exclusive_scan (C++17)

Operations on uninitialized memory

uninitialized_copy
uninitialized_move (C++17)
uninitialized_fill

uninitialized_copy_n (C++11)
uninitialized_move_n (C++17)
uninitialized_fill_n

destroy (C++17)
destroy_n (C++17)
destroy_at (C++17)
construct_at (C++20)

uninitialized_default_construct (C++17)
uninitialized_value_construct (C++17)
uninitialized_default_construct_n (C++17)
uninitialized_value_construct_n (C++17)

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Defined in header`<algorithm>`		(until C++11)
Defined in header`<utility>`		(since C++11)
Defined in header`<string_view>`
template<class T> void swap( T& a, T& b);	(1)	(conditionally noexcept since C++11) (constexpr since C++20)
template<class T2,std::size_t N> void swap( T2(&a)[N], T2(&b)[N]);	(2)	(conditionally noexcept since C++11) (constexpr since C++20)

Exchanges the given values.

1) Swaps the valuesa andb.

This overload participates in overload resolution only ifstd::is_move_constructible_v<T>&&std::is_move_assignable_v<T> istrue.

(since C++17)

2) Swaps the arraysa andb. Equivalent tostd::swap_ranges(a, a+ N, b).

This overload participates in overload resolution only ifstd::is_swappable_v<T2> istrue.

(since C++17)

[edit]Parameters

a, b	-	the values to be swapped
Type requirements
- `T` must meet the requirements ofCopyConstructible andCopyAssignable(until C++11)MoveConstructible andMoveAssignable(since C++11).
- `T2` must meet the requirements ofSwappable.

[edit]Return value

(none)

[edit]Exceptions

(none)	(until C++11)
`noexcept` specification: noexcept( std::is_nothrow_move_constructible<T>::value&& std::is_nothrow_move_assignable<T>::value )	(since C++11)

`noexcept` specification: noexcept(noexcept(swap(a,b))) The lookup for the identifier`swap` in the exception specification finds this function template in addition to anything found by the usual lookup rules, making the exception specification equivalent to C++17std::is_nothrow_swappable.	(since C++11) (until C++17)
`noexcept` specification: noexcept(std::is_nothrow_swappable_v<T2>)	(since C++17)

[edit]Complexity

1) Constant.

2) Linear inN.

[edit]Specializations

std::swap may bespecialized in namespace std for program-defined types, but such specializations are not found byADL (the namespace std is not the associated namespace for the program-defined type).

(until C++20)

The expected way to make aprogram-defined type swappable is to provide a non-member function swap in the same namespace as the type: seeSwappable for details.

The following overloads are already provided by the standard library:

std::swap(std::pair) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::tuple) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::shared_ptr) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::weak_ptr) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::unique_ptr) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::function) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_string)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::array) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::deque)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::forward_list) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::list)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::vector)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::map)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::multimap)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::set)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::multiset)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::unordered_map) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::unordered_multimap) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::unordered_set) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::unordered_multiset) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::queue) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::priority_queue) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::stack) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::valarray) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_stringbuf) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_istringstream) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_ostringstream) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_stringstream) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_filebuf) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_ifstream) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_ofstream) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_fstream) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_syncbuf) (C++20)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_spanbuf) (C++23)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_ispanstream) (C++23)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_ospanstream) (C++23)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_spanstream) (C++23)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_regex) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::match_results) (C++11)	specializes the`std::swap` algorithm (function template)[edit]
std::swap(std::thread) (C++11)	specializes thestd::swap algorithm (function)[edit]
std::swap(std::unique_lock) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::shared_lock) (C++14)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::promise) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::packaged_task) (C++11)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::optional) (C++17)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::any) (C++17)	specializes thestd::swap algorithm (function)[edit]
std::swap(std::variant) (C++17)	specializes thestd::swap algorithm (function template)[edit]
std::swap(std::basic_stacktrace) (C++23)	specializes thestd::swap algorithm (function template)[edit]
swap(std::filesystem::path) (C++17)	specializes thestd::swap algorithm (function)[edit]
swap(std::expected) (C++23)	specializes thestd::swap algorithm (function)[edit]
swap(std::jthread) (C++20)	specializes thestd::swap algorithm (function)[edit]
swap(std::move_only_function) (C++23)	specializes thestd::swap algorithm (function)[edit]
swap(std::stop_source) (C++20)	specializes thestd::swap algorithm (function)[edit]
swap(std::stop_token) (C++20)	specializes thestd::swap algorithm (function)[edit]

[edit]Example

Run this code

#include <algorithm>#include <iostream> namespace Ns{class A{int id{}; friendvoid swap(A& lhs, A& rhs){std::cout<<"swap("<< lhs<<", "<< rhs<<")\n";            std::swap(lhs.id, rhs.id);} friendstd::ostream& operator<<(std::ostream& os, Aconst& a){return os<<"A::id="<< a.id;} public:        A(int i): id{i}{}        A(Aconst&)= delete;        A& operator=(Aconst&)= delete;};} int main(){int a=5, b=3;std::cout<< a<<' '<< b<<'\n';    std::swap(a, b);std::cout<< a<<' '<< b<<'\n';     Ns::A p{6}, q{9};std::cout<< p<<' '<< q<<'\n';//  std::swap(p, q); // error, type requirements are not satisfied    swap(p, q);// OK, ADL finds the appropriate friend `swap`std::cout<< p<<' '<< q<<'\n';}

Output:

5 33 5A::id=6 A::id=9swap(A::id=6, A::id=9)A::id=9 A::id=6

[edit]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 227	C++98	`T` was not required to beCopyConstructible orDefaultConstructible (a temporary object of type`T` might not be able to be constructed)	`T` is also required to beCopyConstructible
LWG 809	C++98	arrays could not be swapped	added overload(2)
LWG 2554	C++11	swapping multi-dimensional arrays can never benoexcept due to name lookup problems	made to work

[edit]See also

ranges::swap (C++20)	swaps the values of two objects (customization point object)[edit]
iter_swap	swaps the elements pointed to by two iterators (function template)[edit]
swap_ranges	swaps two ranges of elements (function template)[edit]
exchange (C++14)	replaces the argument with a new value and returns its previous value (function template)[edit]