std::move_iterator

 

C++

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Concepts library (C++20)

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Technical Specifications

 

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)
Iterator primitives
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_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++20)(C++20)
Algorithm concepts and utilities
Indirect callable concepts
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)
Common algorithm requirements
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)
Utilities
indirect_result_t	projected
Iterator adaptors
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) 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) back_inserter front_inserter inserter
Stream iterators
istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
Iterator customization points
ranges::iter_move (C++20)
ranges::iter_swap (C++20)
Iterator operations
advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
Range access
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)

 

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 an LegacyInputIterator or model input_iterator (since C++20)), 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 models std::derived_from<std::random_access_iterator_tag>, this is std::random_access_iterator_tag. Otherwise, this is std::iterator_traits<Iter>::iterator_category unchanged (since C++20)
iterator_concept (since C++20)	std::input_iterator_tag
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 functions

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

Member objects

Member name	Definition
current (private)	a copy of the base() iterator, the name is for exposition only

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(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+	advances the iterator (function template)
operator-	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 template)
iter_swap (C++20)	swap the objects pointed to by two underlying iterators (function template)

Example

Run this code

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>
#include <numeric>
#include <string>
 
int main()
{
    std::vector<std::string> v{"this", "is", "an", "example"};
 
    std::cout << "Old contents of the vector: ";
    for (auto& s : v)
        std::cout << '"' << s << "\" ";
 
    typedef std::vector<std::string>::iterator iter_t;
    std::string concat = std::accumulate(
                             std::move_iterator<iter_t>(v.begin()),
                             std::move_iterator<iter_t>(v.end()),
                             std::string());  // Can be simplified with std::make_move_iterator
 
    std::cout << "\nConcatenated as string: " << concat << '\n'
              << "New contents of the vector: ";
    for (auto& s : v)
        std::cout << '"' << s << "\" ";
    std::cout << '\n';
}

Possible output:

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

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

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)