std::swap (3) - Linux Manuals
std::swap: std::swap
NAME
Synopsis
Defined in header <algorithm> (until C++11)
Defined in header <utility> (since C++11)
template< class T > (until C++11)
void swap( T& a, T& b );
template< class T > (since C++11)
void swap( T& a, T& b ) noexcept(/* see below */); (until C++20)
template< class T > (1) (since C++20)
constexpr void swap( T& a, T& b ) noexcept(/* see below */);
template< class T2, std::size_t N > (since C++11)
void swap( T2 (&a)[N], T2 (&b)[N]) noexcept(/* see below */); (2) (until C++20)
template< class T2, std::size_t N > (since C++20)
constexpr void swap( T2 (&a)[N], T2 (&b)[N]) noexcept(/* see below */);
Exchanges the given values.
1) Swaps the values a and b.
This overload does not participate in overload resolution unless std::is_move_constructible_v<T> && std::is_move_assignable_v<T> is true.
(since C++17)
2) Swaps the arrays a and b. In effect calls std::swap_ranges(a, a+N, b).
This overload does not participate in overload resolution unless std::is_swappable_v<T2> is true.
(since C++17)
Parameters
a, b - the values to be swapped
Type requirements
-
T must meet the requirements of MoveAssignable and MoveConstructible.
-
T2 must meet the requirements of Swappable.
Return value
(none)
Exceptions
1)
(none) (until C++11)
noexcept specification:
noexcept(
std::is_nothrow_move_constructible<T>::value && (since C++11)
std::is_nothrow_move_assignable<T>::value
)
2)
noexcept specification:
noexcept(noexcept(swap(*a, *b))) (until C++17)
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++17 std::is_nothrow_swappable.
noexcept specification: (since C++17)
noexcept(std::is_nothrow_swappable_v<T2>)
Complexity
1) Constant
2) Linear in N
Specializations
std::swap may be specialized_in_namespace_std for program-defined types, but such specializations are not found by ADL (the namespace std is not the associated namespace for the program-defined type). (until C++20)
The expected way to make a program-defined type swappable is to provide a non-member function swap in the same namespace as the type: see Swappable for details.
The following overloads are already provided by the standard library:
std::swap(std::pair) specializes the std::swap algorithm
(C++11)
std::swap(std::tuple) specializes the std::swap algorithm
(C++11)
std::swap(std::shared_ptr) specializes the std::swap algorithm
(C++11)
std::swap(std::weak_ptr) specializes the std::swap algorithm
(C++11)
std::swap(std::unique_ptr) specializes the std::swap algorithm
(C++11)
std::swap(std::function) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_string) (function template)
std::swap(std::array) specializes the std::swap algorithm
(C++11)
std::swap(std::deque) (function template)
std::swap(std::forward_list) specializes the std::swap algorithm
(C++11)
std::swap(std::list) (function template)
std::swap(std::vector) (function template)
std::swap(std::map) (function template)
std::swap(std::multimap) (function template)
std::swap(std::set) (function template)
std::swap(std::multiset) (function template)
std::swap(std::unordered_map) specializes the std::swap algorithm
(C++11)
std::swap(std::unordered_multimap) specializes the std::swap algorithm
(C++11)
std::swap(std::unordered_set) specializes the std::swap algorithm
(C++11)
std::swap(std::unordered_multiset) specializes the std::swap algorithm
(C++11)
std::swap(std::queue) (function template)
std::swap(std::priority_queue) (function template)
std::swap(std::stack) (function template)
std::swap(std::valarray) specializes the std::swap() algorithm
(C++11)
std::swap(std::basic_stringbuf) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_istringstream) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_ostringstream) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_stringstream) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_filebuf) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_ifstream) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_ofstream) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_fstream) specializes the std::swap algorithm
(C++11)
std::swap(std::basic_syncbuf) specializes the std::swap algorithm
(C++20)
std::swap(std::basic_regex) specializes the std::swap algorithm
(C++11)
std::swap(std::match_results) specializes the std::swap() algorithm
(C++11)
std::swap(std::thread) specializes the std::swap algorithm
(C++11)
std::swap(std::unique_lock) specialization of std::swap for unique_lock
(C++11)
std::swap(std::promise) specializes the std::swap algorithm
(C++11)
std::swap(std::packaged_task) specializes the std::swap algorithm
(C++11)
std::swap(std::optional) specializes the std::swap algorithm
(C++17)
std::swap(std::any) specializes the std::swap algorithm
(C++17)
std::swap(std::variant) specializes the std::swap algorithm
(C++17)
swap(std::filesystem::path) (function)
Example
// Run this code
Output:
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_2554 C++11 swapping multi-dimensional arrays can never be noexcept due to name lookup problems made to work
See also
iter_swap (function template)
swap_ranges (function template)
exchange replaces the argument with a new value and returns its previous value
(C++14)
