std::iter_swap() algorithm

od C++20

// (1)
template< class ForwardIt1, class ForwardIt2 >
constexpr void iter_swap( ForwardIt1 a, ForwardIt2 b );

do C++20

// (1)
template< class ForwardIt1, class ForwardIt2 >
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	LegacyForwardIterator
*a *b	Swappable

Return value

(none)

Complexity

Constant.

Exceptions

(none)

Possible implementation

iter_swap(1)

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

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.

Examples

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

Main.cpp

#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';
}

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