std::iter_swap

Header: <algorithm>

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

# Declarations

template< class ForwardIt1, class ForwardIt2 >
void iter_swap( ForwardIt1 a, ForwardIt2 b );

(constexpr since C++20)

# Parameters

a, b: iterators to the elements to swap

# Return value

(none)

# 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.

# Example

#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);
}

# Defect reports

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)