std::iter_swap

 

C++

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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 Batch operations for_each for_each_n (C++17) Search operations 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) C library qsort bsearch
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iota (C++11) inner_product adjacent_difference    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)

 

Defined in header <algorithm>
template< class ForwardIt1, class ForwardIt2 > void iter_swap( ForwardIt1 a, ForwardIt2 b );		(until C++20)
template< class ForwardIt1, class ForwardIt2 > constexpr void iter_swap( ForwardIt1 a, ForwardIt2 b );		(since C++20)

Swaps the values of the elements the given iterators are pointing to.

Parameters

a, b	-	iterators to the elements to swap
Type requirements
- ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
- *a, *b must meet the requirements of Swappable.

Return value

(none)

Complexity

constant

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.

Possible implementation

template<class ForwardIt1, class ForwardIt2> constexpr void iter_swap(ForwardIt1 a, ForwardIt2 b) // constexpr since C++20 { using std::swap; swap(*a, *b); }

Example

The following is an implementation of selection sort in C++.

Run this code

#include <algorithm>
#include <functional>
#include <iostream>
#include <random>
#include <vector>
 
template<class ForwardIt>
void selection_sort(ForwardIt begin, ForwardIt end)
{
    for (ForwardIt i = begin; i != end; ++i)
        std::iter_swap(i, std::min_element(i, end));
}
 
int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_int_distribution<> dist(-9, +9);
    std::vector<int> v;
    std::generate_n(back_inserter(v), 20, bind(dist, gen));
 
    std::cout << "Before sort: " << std::showpos;
    for (auto e : v)
        std::cout << e << ' ';
 
    selection_sort(v.begin(), v.end());
 
    std::cout << "\nAfter sort : ";
    for (auto e : v)
        std::cout << e << ' ';
    std::cout << '\n';
}

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

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)

See also

swap	swaps the values of two objects (function template)
swap_ranges	swaps two ranges of elements (function template)
iter_swap (C++20)	swaps the objects pointed to by two adjusted underlying iterators (function template)
iter_swap (C++20)	swaps the objects pointed to by two underlying iterators (function template)
iter_swap (C++20)	swaps the values referenced by two dereferenceable objects (customization point object)