< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
Operations on uninitialized storage
C library
Defined in header <algorithm>
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.


[edit] 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.

[edit] Return value


[edit] Complexity


[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 void iter_swap(ForwardIt1 a, ForwardIt2 b) // constexpr since C++20
    using std::swap;
    swap(*a, *b);

[edit] Example

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

#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) [edit]
swaps two ranges of elements
(function template) [edit]
swaps the objects pointed to by two adjusted underlying iterators
(function template) [edit]
swaps the objects pointed to by two underlying iterators
(function template) [edit]
swaps the values referenced by two dereferenceable objects
(customization point object) [edit]