std::ranges::iota, std::ranges::iota_result
From cppreference.com
| Defined in header <numeric>
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| Call signature |
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| template< std::input_or_output_iterator O, std::sentinel_for<O> S, std::weakly_incrementable T > |
(1) | (since C++23) |
| template< std::weakly_incrementable T, ranges::output_range<const T&> R > constexpr iota_result<ranges::borrowed_iterator_t<R>, T> |
(2) | (since C++23) |
| Helper types |
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| template< class O, class T > using iota_result = ranges::out_value_result<O, T>; |
(3) | (since C++23) |
Fills the range [first, last) with sequentially increasing values, starting with value and repetitively evaluating ++value.
Equivalent operation:
*(first) = value; *(first + 1) = ++value; *(first + 2) = ++value; *(first + 3) = ++value; ...
Contents |
[edit] Parameters
| first, last | - | the range of elements to fill with sequentially increasing values starting with value |
| value | - | initial value to store; the expression ++value must be well-formed |
[edit] Return value
{last, value + ranges::distance(first, last)}
[edit] Complexity
Exactly last - first increments and assignments.
[edit] Possible implementation
struct iota_fn { template<std::input_or_output_iterator O, std::sentinel_for<O> S, std::weakly_incrementable T> requires std::indirectly_writable<O, const T&> constexpr iota_result<O, T> operator()(O first, S last, T value) const { while (first != last) { *first = as_const(value); ++first; ++value; } return {std::move(first), std::move(value)}; } template<std::weakly_incrementable T, std::ranges::output_range<const T&> R> constexpr iota_result<std::ranges::borrowed_iterator_t<R>, T> operator()(R&& r, T value) const { return (*this)(std::ranges::begin(r), std::ranges::end(r), std::move(value)); } }; inline constexpr iota_fn iota; |
[edit] Notes
The function is named after the integer function ⍳ from the programming language APL.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_iota |
202202L | (C++23) | std::ranges::iota
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[edit] Example
Uses the vector of iterators (std::vector<std::list<T>::iterator>) as a proxy to shuffle the elements of the std::list, because ranges::shuffle cannot be applied to the std::list directly.
Run this code
#include <algorithm> #include <functional> #include <iostream> #include <list> #include <numeric> #include <random> #include <vector> template <typename Proj = std::identity> void println(auto comment, std::ranges::input_range auto&& range, Proj proj = {}) { for (std::cout << comment; auto const &element : range) std::cout << proj(element) << ' '; std::cout << '\n'; } int main() { std::list<int> list(8); // Fill the list with ascending values: 0, 1, 2, ..., 7 std::ranges::iota(list, 0); println("List: ", list); // A vector of iterators (see the comment to Example) std::vector<std::list<int>::iterator> vec(list.size()); // Fill with iterators to consecutive list's elements std::ranges::iota(vec.begin(), vec.end(), list.begin()); std::ranges::shuffle(vec, std::mt19937 {std::random_device {}()}); println("List viewed via vector: ", vec, [](auto it) { return *it; }); }
Possible output:
List: 0 1 2 3 4 5 6 7 List viewed via vector: 5 7 6 0 1 3 4 2
[edit] See also
| copy-assigns the given value to every element in a range (function template) | |
| (C++20) |
assigns a range of elements a certain value (niebloid) |
| assigns the results of successive function calls to every element in a range (function template) | |
| (C++20) |
saves the result of a function in a range (niebloid) |
| (C++20) |
a view consisting of a sequence generated by repeatedly incrementing an initial value(class template) (customization point object) |
| (C++11) |
fills a range with successive increments of the starting value (function template) |
