NAME¶

std::move_iterator - std::move_iterator

Synopsis¶

Defined in header <iterator>
template< class Iter > (since C++11)
class move_iterator;

std::move_iterator is an iterator adaptor which behaves exactly like the underlying
iterator (which must be at least a LegacyInputIterator
or model input_iterator
(since C++20)
, or stronger iterator concept
(since C++23)), except that dereferencing converts the value returned by the
underlying iterator into an rvalue. If this iterator is used as an input iterator,
the effect is that the values are moved from, rather than copied from.

Member functions¶

constructor constructs a new iterator adaptor
(C++11) (public member function)
operator= assigns another iterator adaptor
(C++11) (public member function)
base accesses the underlying iterator
(C++11) (public member function)
operator*
operator-> accesses the pointed-to element
(C++11) (public member function)
(C++11)(deprecated in C++20)
operator[] accesses an element by index
(C++11) (public member function)
operator++
operator++(int)
operator+=
operator+ advances or decrements the iterator
operator-- (public member function)
operator--(int)
operator-=
operator-
(C++11)

Non-member functions¶

operator==
operator!=
operator<
operator<=
operator>
operator>=
operator<=> compares the underlying iterators
(C++11) (function template)
(C++11)(removed in C++20)
(C++11)
(C++11)
(C++11)
(C++11)
(C++20)
operator==(std::move_sentinel) compares the underlying iterator and the underlying
(C++20) sentinel
(function template)
operator+ advances the iterator
(C++11) (function template)
operator- computes the distance between two iterator adaptors
(C++11) (function template)
operator-(std::move_sentinel) computes the distance between the underlying iterator
(C++20) and the underlying sentinel
(function template)
iter_move casts the result of dereferencing the underlying
(C++20) iterator to its associated rvalue reference type
(function)
iter_swap swaps the objects pointed to by two underlying
(C++20) iterators
(function template)
make_move_iterator creates a std::move_iterator of type inferred from
(C++11) the argument
(function template)

Helper templates

template< class Iterator1, class Iterator2 >

requires (!std::sized_sentinel_for<Iterator1, Iterator2>)
constexpr bool disable_sized_sentinel_for< (since C++20)
std::move_iterator<Iterator1>,

std::move_iterator<Iterator2>> = true;

This partial specialization of std::disable_sized_sentinel_for prevents
specializations of move_iterator from satisfying sized_sentinel_for if their
underlying iterators do not satisfy the concept.

Notes¶

Feature-test macro Value Std Feature
__cpp_lib_move_iterator_concept 202207L (C++23) Make std::move_iterator<T*> a random
access iterator

Example¶

// Run this code

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <ranges>
#include <string>
#include <string_view>
#include <vector>

void print(const std::string_view rem, const auto& v)
{
std::cout << rem;
for (const auto& s : v)
std::cout << std::quoted(s) << ' ';
std::cout << '\n';
};

int main()
{
std::vector<std::string> v{"this", "_", "is", "_", "an", "_", "example"};
print("Old contents of the vector: ", v);
std::string concat;
for (auto begin = std::make_move_iterator(v.begin()),
end = std::make_move_iterator(v.end());
begin != end; ++begin)
{
std::string temp{*begin}; // moves the contents of *begin to temp
concat += temp;
}

// Starting from C++17, which introduced class template argument deduction,
// the constructor of std::move_iterator can be used directly:
// std::string concat = std::accumulate(std::move_iterator(v.begin()),
// std::move_iterator(v.end()),
// std::string());

print("New contents of the vector: ", v);
print("Concatenated as string: ", std::ranges::single_view(concat));
}

Possible output:¶

Old contents of the vector: "this" "_" "is" "_" "an" "_" "example"
New contents of the vector: "" "" "" "" "" "" ""
Concatenated as string: "this_is_an_example"

Defect reports

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

DR Applied Behavior as published Correct behavior
to
dereferencing a move_iterator could return a
LWG 2106 C++11 dangling reference returns the
if the dereferencing the underlying iterator object instead
returns a prvalue
LWG 3736 C++20 move_iterator was missing added
disable_sized_sentinel_for specialization
member iterator_category was defined even if iterator_category
P2259R1 C++20 std::iterator_traits<Iter>::iterator_category is is
not defined not defined in
this case

See also¶

make_move_iterator creates a std::move_iterator of type inferred from the argument
(C++11) (function template)
move_sentinel sentinel adaptor for use with std::move_iterator
(C++20) (class template)