std::iter_swap
From cppreference.com
| Defined in header <algorithm>
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| template< class ForwardIt1, class ForwardIt2 > void iter_swap( ForwardIt1 a, ForwardIt2 b ); |
(constexpr since C++20) | |
Swaps the values of the elements the given iterators are pointing to.
If any of the following conditions is satisfied, the behavior is undefined:
- a or b is not dereferenceable.
- *a is not Swappable with *b.
Contents |
[edit] Parameters
| a, b | - | iterators to the elements to swap |
| Type requirements | ||
-ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
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[edit] Return value
(none)
[edit] Complexity
Constant.
[edit] Notes
This function template models the semantics of the swap operation given by Swappable. That is, overloads of swap found by ADL and the fall back of std::swap are considered.
[edit] Possible implementation
template<class ForwardIt1, class ForwardIt2> constexpr //< since C++20 void iter_swap(ForwardIt1 a, ForwardIt2 b) { using std::swap; swap(*a, *b); } |
[edit] Example
The following is an implementation of selection sort in C++.
Run this code
#include <algorithm> #include <iostream> #include <random> #include <string_view> #include <vector> template<class ForwardIt> void selection_sort(ForwardIt begin, ForwardIt end) { for (ForwardIt it = begin; it != end; ++it) std::iter_swap(it, std::min_element(it, end)); } void println(std::string_view rem, std::vector<int> const& v) { std::cout << rem; for (int e : v) std::cout << e << ' '; std::cout << '\n'; } template<int min, int max> int rand_int() { static std::uniform_int_distribution dist(min, max); static std::mt19937 gen(std::random_device{}()); return dist(gen); } int main() { std::vector<int> v; std::generate_n(std::back_inserter(v), 20, rand_int<-9, +9>); std::cout << std::showpos; println("Before sort: ", v); selection_sort(v.begin(), v.end()); println("After sort: ", v); }
Possible output:
Before sort: -9 -3 +2 -8 +0 -1 +8 -4 -5 +1 -4 -5 +4 -9 -8 -6 -6 +8 -4 -6 After sort: -9 -9 -8 -8 -6 -6 -6 -5 -5 -4 -4 -4 -3 -1 +0 +1 +2 +4 +8 +8
[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 187 | C++98 | it was unspecified whether swap is used | the effect is equivalent to swap(*a, *b) |
[edit] See also
| swaps the values of two objects (function template) | |
| swaps two ranges of elements (function template) | |
| (C++20) |
swaps the objects pointed to by two adjusted underlying iterators (function template) |
| (C++20) |
swaps the objects pointed to by two underlying iterators (function template) |
| (C++20) |
swaps the values referenced by two dereferenceable objects (customization point object) |
