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std::counted_iterator

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< cpp‎ | iterator

Compiler support

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Named requirements

Feature test macros (C++20)

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Technical specifications

External libraries

Iterator library

Iterator concepts

indirectly_readable

(C++20)

indirectly_writable

(C++20)

weakly_incrementable

(C++20)

(C++20)

is-integer-like
is-signed-integer-like

(C++20)(C++20)

(C++20)

sized_sentinel_for

(C++20)

(C++20)

output_iterator

(C++20)

input_or_output_iterator

(C++20)

forward_iterator

(C++20)

bidirectional_iterator

(C++20)

random_access_iterator

(C++20)

contiguous_iterator

(C++20)

Iterator primitives

input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag

(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)

(deprecated in C++17)

iterator_traits

incrementable_traits

(C++20)

indirectly_readable_traits

(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)

(C++20)

(C++20)

(C++20)

indirect_result_t

(C++20)

(C++20)

projected_value_t

(C++26)

Iterator adaptors

reverse_iterator

make_reverse_iterator

(C++14)

(C++11)

make_move_iterator

(C++11)

default_sentinel_tdefault_sentinel

(C++20)(C++20)

unreachable_sentinel_tunreachable_sentinel

(C++20)(C++20)

front_insert_iterator

back_insert_iterator

insert_iterator

(C++20)

common_iterator

(C++20)

counted_iterator

(C++20)

basic_const_iterator

(C++23)

(C++23)

(C++23)

make_const_iterator

(C++23)

make_const_sentinel

(C++23)

Stream iterators

istream_iterator

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ostreambuf_iterator

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ranges::iter_move

(C++20)

ranges::iter_swap

(C++20)

Iterator operations

(C++11)

(C++11)

ranges::advance

(C++20)

ranges::distance

(C++20)

(C++20)

(C++20)

(C++11)(C++14)

(C++14)(C++14)

(C++11)(C++14)

(C++14)(C++14)

(C++17)(C++20)

(C++17)

(C++17)

std::counted_iterator

Member functions

counted_iterator::counted_iterator

counted_iterator::operator=

counted_iterator::base

counted_iterator::count

counted_iterator::operator*counted_iterator::operator->

counted_iterator::operator[]

counted_iterator::operator++counted_iterator::operator++(int)counted_iterator::operator+counted_iterator::operator+=counted_iterator::operator--counted_iterator::operator--(int)counted_iterator::operator-counted_iterator::operator-=

Non-member functions

operator==operator<=>

(C++20)(C++20)

operator==(default_sentinel_t)

(C++20)

(C++20)

(C++20)

operator-(default_sentinel_t)

(C++20)

(C++20)

(C++20)

iterator_traits<std::counted_iterator>

(C++20)

Defined in header <iterator>

template< std::input_or_output_iterator I >
class counted_iterator;

(since C++20)

std::counted_iterator is an iterator adaptor which behaves exactly like the underlying iterator, except that it keeps track of the distance to the end of its range. This iterator is equal to std::default_sentinel if and only if its count reaches zero.

Contents

[edit] Member types

Member type Definition

iterator_type I

value_type
(conditionally present) std::iter_value_t <I> if I models indirectly_readable; otherwise, not defined

difference_type std::iter_difference_t <I>

iterator_concept
(conditionally present) I::iterator_concept if present; otherwise, not defined

iterator_category
(conditionally present) I::iterator_category if present; otherwise, not defined

[edit] Member objects

Member name Definition

current (private) the underlying iterator which base() accesses
(exposition-only member object*)

length (private) the distance between the underlying iterator and the end of its range
(exposition-only member object*)

[edit] Member functions

constructs a new counted_iterator
(public member function) [edit]

assigns another counted_iterator
(public member function) [edit]

accesses the underlying iterator
(public member function) [edit]

returns the distance to the end
(public member function) [edit]

operator*operator->

accesses the pointed-to element
(public member function) [edit]

accesses an element by index
(public member function) [edit]

operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator-

advances or decrements the counted_iterator
(public member function) [edit]

[edit] Non-member functions

operator==operator<=>

(C++20)

compares the distances to the end
(function template) [edit]

operator==(std::default_sentinel)

(C++20)

checks if the distance to the end is equal to 0
(function template) [edit]

(C++20)

advances the iterator
(function template) [edit]

(C++20)

computes the distance between two iterator adaptors
(function template) [edit]

operator-(std::default_sentinel_t)

(C++20)

computes the signed distance to the end
(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]

[edit] Helper classes

std::iterator_traits<std::counted_iterator>

(C++20)

provides uniform interface to the properties of the std::counted_iterator type
(class template specialization) [edit]

[edit] Example

Run this code

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
 
using std::operator""s;
 
void print(auto const remark, auto const& v)
{
 const auto size = std::ssize (v);
 std::cout << remark << '[' << size << "] { ";
 for (auto it = std::counted_iterator{std::cbegin (v), size};
 it != std::default_sentinel ; ++it)
 std::cout << *it << (it.count() > 1 ? ", " : " ");
 std::cout << "}\n";
}
 
int main()
{
 const auto src = {"Arcturus"s, "Betelgeuse"s, "Canopus"s, "Deneb"s, "Elnath"s};
 print("src", src);
 std::vector <decltype(src)::value_type> dst;
 std::ranges::copy (std::counted_iterator{src.begin(), 3},
 std::default_sentinel,
 std::back_inserter (dst));
 print("dst", dst);
}

Output:

src[5] { Arcturus, Betelgeuse, Canopus, Deneb, Elnath }
dst[3] { Arcturus, Betelgeuse, Canopus }

[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
P2259R1	C++20	member typedefs are not provided std::incrementable_traits is specialized for `counted_iterator`	member typedefs are added to account for `iterator_traits` fix redundant std::incrementable_traits specialization is removed

[edit] See also

default_sentinel_t

(C++20)

default sentinel for use with iterators that know the bound of their range
(class) [edit]

(C++20)

creates a subrange from an iterator and a count
(customization point object)[edit]

ranges::take_viewviews::take

(C++20)

a view consisting of the first N elements of another view
(class template) (range adaptor object)[edit]

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