std::move_iterator

 

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Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) output_iterator (C++20) forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
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iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (deprecated in C++17)	incrementable_traits (C++20) indirectly_readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)
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indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)   indirect_unary_predicate (C++20)	indirect_binary_predicate (C++20) indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
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indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20) indirectly_copyable_storable (C++20)	indirectly_swappable (C++20) indirectly_comparable (C++20) permutable (C++20) mergeable (C++20) sortable (C++20)
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indirect_result_t (C++20)	projected (C++20)
Iterator adaptors
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) make_const_iterator (C++23) make_const_sentinel (C++23) back_inserter front_inserter inserter
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istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
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ranges::iter_move (C++20)
ranges::iter_swap (C++20)
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advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
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begincbegin (C++11)(C++14) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

std::move_iterator

Member functions

move_iterator::move_iterator

move_iterator::operator=

move_iterator::base

move_iterator::operator*move_iterator::operator->

move_iterator::operator[]

move_iterator::operator++move_iterator::operator+move_iterator::operator+=move_iterator::operator--move_iterator::operator-move_iterator::operator-=

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(C++20)

operator==(move_sentinel) (C++20)

operator+

operator-

operator-(move_sentinel) (C++20)

iter_move (C++20)

iter_swap (C++20)

make_move_iterator (C++11)

 

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

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 types

Member type	Definition
iterator_type	Iter
iterator_category	std::iterator_traits<Iter>::iterator_category (until C++20) If std::iterator_traits<Iter>::iterator_category is valid and denotes a type: if std::iterator_traits<Iter>::iterator_category models std::derived_from<std::random_access_iterator_tag>, member iterator_category is std::random_access_iterator_tag. Otherwise, member iterator_category is the same type as std::iterator_traits<Iter>::iterator_category. Otherwise, there is no member iterator_category. (since C++20)
iterator_concept	std::input_iterator_tag (since C++20) (until C++23) std::random_access_iterator_tag, if Iter models std::random_access_iterator. Otherwise, std::bidirectional_iterator_tag, if Iter models std::bidirectional_iterator. Otherwise, std::forward_iterator_tag, if Iter models std::forward_iterator. Otherwise, std::input_iterator_tag. (since C++23)
value_type	std::iterator_traits<Iter>::value_type (until C++20) std::iter_value_t<Iter> (since C++20)
difference_type	std::iterator_traits<Iter>::difference_type (until C++20) std::iter_difference_t<Iter> (since C++20)
pointer	Iter
reference	If std::iterator_traits<Iter>::reference is a reference, this is the rvalue reference version of the same type. Otherwise (such as if the wrapped iterator returns by value), this is std::iterator_traits<Iter>::reference unchanged (until C++20) std::iter_rvalue_reference_t<Iter> (since C++20)

Member objects

Member name	Definition
current (private)	the underlying iterator from which base() copies or moves (since C++20) (exposition-only member object*)

Member functions

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

Non-member functions

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

Notes

Feature-test macro	Value	Std	Comment
__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 <numeric>
#include <string>
#include <vector>
 
int main()
{
    std::vector<std::string> v{"this", "_", "is", "_", "an", "_", "example"};
 
    auto print_v = [&](auto const rem)
    {
        std::cout << rem;
        for (const auto& s : v)
            std::cout << std::quoted(s) << ' ';
        std::cout << '\n';
    };
 
    print_v("Old contents of the vector: ");
 
    std::string concat = std::accumulate(std::make_move_iterator(v.begin()),
                                         std::make_move_iterator(v.end()),
                                         std::string());
 
    // An alternative that uses std::move_iterator directly could be:
    // using moviter_t = std::move_iterator<std::vector<std::string>::iterator>;
    // std::string concat = std::accumulate(moviter_t(v.begin()),
    //                                      moviter_t(v.end()),
    //                                      std::string());
 
    // Starting from C++17, which introduced class template argument deduction,
    // the constructor of std::move_iterator can be used directly without
    // template parameters in most cases:
    // std::string concat = std::accumulate(std::move_iterator(v.begin()),
    //                                      std::move_iterator(v.end()),
    //                                      std::string());
 
    print_v("New contents of the vector: ");
 
    std::cout << "Concatenated as string: " << quoted(concat) << '\n';
}

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 to	Behavior as published	Correct behavior
LWG 2106	C++11	dereferencing a move_iterator could return a dangling reference if the dereferencing the underlying iterator returns a prvalue	returns the object instead
P2259R1	C++20	member iterator_category was always defined	defined only if std::iterator_traits<Iter>::iterator_category exists

See also

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