std::iter_swap(3)

💅 std::iter_swap(3) 💅

okay bestie, welcome to the std::iter_swap(3) page from the C++ Standard Libary manual. this one is short, sweet, and swaps stuff. ✨

💖 NAME 💖

std::iter_swap - std::iter_swap. yes literally, the name is the name. iconic. 💅

🦋 Synopsis 🦋

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

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

If any of the following conditions is satisfied, the behavior is undefined — not cute, not safe, do not pass go:

• a or b is not dereferenceable.
• *a is not Swappable with *b.

🎀 Parameters 🎀

• a, b — iterators to the elements to swap.

🌸 Type requirements 🌸

• ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

✨ Return value ✨

(none) — she returns nothing. no notes. 💅

🔥 Complexity 🔥

Constant. literally constant, no dramatic growth arc.

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

🌈 Example 🌈

The following is an implementation of selection sort in C++. There’s a // Run this code link in the original, and here’s the whole thing:

#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

👑 Defect reports 👑

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• DR: LWG 187; Applied to: C++98; Behavior as published: it was unspecified whether swap is used; Correct behavior: 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 — swaps the objects pointed to by two adjusted underlying iterators (C++20) (function template).
• iter_swap — swaps the objects pointed to by two underlying iterators (C++20) (function template).
• iter_swap — swaps the values referenced by two dereferenceable objects (C++20) (customization point object).

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source: http://cppreference.com · version/date: 2024.06.10 · page: std::iter_swap(3) — bye bestie, go swap responsibly! 💖