NAME¶

iter_swap(std::common_iterator) - iter_swap(std::common_iterator)

Synopsis¶

template< std::indirectly_swappable<I> I2, class S2 >

friend constexpr void
iter_swap( const common_iterator& x, (since C++20)

const std::common_iterator<I2, S2>& y ) noexcept(/*see
below*/);

Swaps the objects pointed to by two underlying iterators. The behavior is undefined
if x does not hold an I object or y does not hold an I2 object (i.e. at least one of
x and y does not hold an iterator).

The function body is equivalent to ranges::iter_swap(std::get<I>(x.var),
std::get<I2>(y.var)).

This function template is not visible to ordinary unqualified or qualified lookup,
and can only be found by argument-dependent lookup when std::common_iterator<I,S> is
an associated class of the arguments.

Parameters¶

x, y - the iterators to the elements to swap

Return value¶

(none)

Complexity¶

Constant.

Exceptions¶

noexcept specification:
noexcept(noexcept(ranges::iter_swap(std::declval<const I&>(), std::declval<const
I2&>())))

Example¶

// Run this code

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>

int main()
{
std::vector<std::string> v1{"1", "2", "3", "4", "5"},
v2{"α", "β", "γ", "δ", "ε"};

using CI = std::common_iterator<
std::counted_iterator<std::vector<std::string>::iterator>,
std::default_sentinel_t
>;

CI first1{std::counted_iterator{v1.begin(), 3}};
CI first2{std::counted_iterator{v2.begin(), 4}};
CI last{std::default_sentinel};

auto print = [&](auto rem)
{
std::cout << rem << "v1 = ";
std::ranges::copy(v1, std::ostream_iterator<std::string>{std::cout, " "});
std::cout << "\nv2 = ";
std::ranges::copy(v2, std::ostream_iterator<std::string>{std::cout, " "});
std::cout << '\n';
};

print("Before iter_swap:\n");

for (; first1 != last && first2 != last; ++first1, ++first2)
iter_swap(first1, first2); // ADL

print("After iter_swap:\n");
}

Output:¶

Before iter_swap:
v1 = 1 2 3 4 5
v2 = α β γ δ ε
After iter_swap:
v1 = α β γ 4 5
v2 = 1 2 3 δ ε

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 3574 C++20 variant was fully constexpr (P2231R1) but also made constexpr
common_iterator was not

See also¶

swap swaps the values of two objects
(function template)
swap_ranges swaps two ranges of elements
(function template)
iter_swap swaps the elements pointed to by two iterators
(function template)
iter_swap swaps the values referenced by two dereferenceable objects
(C++20) (customization point object)
iter_swap swaps the objects pointed to by two underlying iterators
(C++20) (function template)

Category:¶

* conditionally noexcept