std::ranges::iota, std::ranges::iota_result
From cppreference.com
Defined in header <numeric> | ||
Call signature | ||
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 | ||
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 iterator-sentinel pair defining 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));}}; inlineconstexpr 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 |
[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_rangeauto&& range, Proj proj ={}){for(std::cout<< comment;autoconst&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 (algorithm function object) |
| 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 (algorithm function object) |
(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) |
