std::counted_iterator<I>:: counted_iterator

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C++
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
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)
std::counted_iterator
constexpr counted_iterator ( ) requires std:: default_initializable < I > = default ;
(1) (since C++20)
constexpr counted_iterator ( I x, std:: iter_difference_t < I > n ) ;
(2) (since C++20)
template < class I2 >

requires std:: convertible_to < const I2 & , I >

constexpr counted_iterator ( const counted_iterator < I2 > & other ) ;
(3) (since C++20)

Constructs a new iterator adaptor.

1) Default constructor. Value-initializes the underlying iterator and initialized the underlying length with ​ 0 ​ . Operations on the resulting iterator have defined behavior if and only if the corresponding operations on a value-initialized I also have defined behavior.
2) The underlying iterator is initialized with std :: move ( x ) and the underlying length is initialized with n . The behavior is undefined if n is negative.
3) The underlying iterator and length are initialized with those of other .

Parameters

x - iterator to adapt
n - distance to the end
other - iterator adaptor to convert

Example

Run this code 
#include <algorithm>
#include <initializer_list>
#include <iostream>
#include <iterator>
 
int main()
{
    static constexpr auto pi = {3, 1, 4, 1, 5, 9, 2};
 
    // (1) default constructor:
    constexpr std::counted_iterator<std::initializer_list<int>::iterator> i1{};
    static_assert(i1 == std::default_sentinel);
    static_assert(i1.count() == 0);
 
    // (2) initializes the iterator and length respectively:
    constexpr std::counted_iterator<std::initializer_list<int>::iterator> i2{
        pi.begin(), pi.size() - 2
    };
    static_assert(i2.count() == 5);
    static_assert(*i2 == 3 && i2[1] == 1);
 
    // (3) converting-constructor:
    std::counted_iterator<std::initializer_list<const int>::iterator> i3{i2};
 
    std::ranges::copy(i3, std::default_sentinel,
        std::ostream_iterator<const int>{std::cout, " "});
}

Output: 

3 1 4 1 5

See also

(C++20)
assigns another iterator adaptor
(public member function)
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