Namespaces
Variants
Views
Actions

std::move_iterator

From cppreference.com
< cpp‎ | iterator
 
 
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
Iterator adaptors
Iterator customization points
Iterator operations
(C++11)    
(C++11)
Range access
(C++11)(C++14)
(C++14)(C++14)    
(C++11)(C++14)
(C++14)(C++14)    
(C++17)(C++20)
(C++17)
(C++17)
 
 
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.

Contents

[edit] Nested types

Name 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:

Otherwise, there is no member iterator_category.

(since C++20)
iterator_concept
(since C++20)

std::input_iterator_tag

(until C++23)
(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)

[edit] Data members

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

[edit] Member functions

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

[edit] Non-member functions

(C++11)(C++11)(removed in C++20)(C++11)(C++11)(C++11)(C++11)(C++20)
compares the underlying iterators
(function template) [edit]
compares the underlying iterator and the underlying sentinel
(function template) [edit]
(C++11)
advances the iterator
(function template) [edit]
(C++11)
computes the distance between two iterator adaptors
(function template) [edit]
computes the distance between the underlying iterator and the underlying sentinel
(function template) [edit]
(C++20)
casts the result of dereferencing the underlying iterator to its associated rvalue reference type
(function) [edit]
(C++20)
swaps the objects pointed to by two underlying iterators
(function template) [edit]
creates a std::move_iterator of type inferred from the argument
(function template) [edit]

[edit] Helper templates

template< class Iterator1, class Iterator2 >

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

    std::move_iterator<Iterator2>> = true;
(since C++20)

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.

[edit] Notes

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

[edit] Example

#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"

[edit] 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
LWG 3736 C++20 move_iterator was missing disable_sized_sentinel_for specialization added
P2259R1 C++20 member iterator_category was defined even if
std::iterator_traits<Iter>::iterator_category is not defined
iterator_category is
not defined in this case

[edit] See also

creates a std::move_iterator of type inferred from the argument
(function template) [edit]
sentinel adaptor for use with std::move_iterator
(class template) [edit]