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std::counted_iterator<I>::operator[] - cppreference.com

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constexpr decltype(auto) operator[]( std::iter_difference_t<I> n ) const requires std::random_access_iterator<I>;

 (since C++20)

Accesses the element at specified relative location. The behavior is undefined if n is not less than the recorded distance to the end.

Parameters

n - position relative to current location

Return value

this->base()[n]

Example

#include <array>
#include <iostream>
#include <iterator>
#include <list>

int main()
{
    std::array array{'A', 'B', 'C', 'D', 'E'};

    std::counted_iterator it{array.begin() + 1, /*count:*/ 3};

    for (int i{}; i != it.count(); ++i)
        std::cout << it[i] << ' ';
    std::cout << '\n';

    for (int i{}; i != it.count(); ++i)
        it[i] += ('E' - 'A');

    for (int i{}; i != it.count(); ++i)
        std::cout << it[i] << ' ';
    std::cout << '\n';

    std::list list{'X', 'Y', 'Z', 'W'};
    std::counted_iterator it2{list.begin(), 3};
//  char x = it2[0]; // Error: requirement `random_access_iterator` was not satisfied.
    std::cout << *it2 << '\n'; // OK
}

Output:

See also