NAME

std::iter_swap - std::iter_swap

Synopsis

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

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 <random>
#include <vector>
#include <iostream>
#include <algorithm>
#include <functional>

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