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> iota( R&& r, T value ); |
(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; ...
Parameters
| first, last | - | the range of elements to fill with sequentially increasing values starting with value
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| value | - | initial value to store; the expression ++value must be well-formed |
Return value
{last, value + ranges::distance(first, last)}
Complexity
Exactly last - first increments and assignments.
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; |
Notes
The function is named after the integer function ⍳ from the programming language APL.
| Feature-test macro: | __cpp_lib_ranges_iota |
Example
The following example applies ranges::shuffle to a vector of std::lists' iterators since ranges::shuffle cannot be applied to a std::list directly. ranges::iota is used to populate both containers.
Run this code
#include <algorithm> #include <iostream> #include <list> #include <numeric> #include <random> #include <vector> int main() { std::list<int> l(10); std::ranges::iota(l.begin(), l.end(), -4); std::vector<std::list<int>::iterator> v(l.size()); std::ranges::iota(v, l.begin()); std::ranges::shuffle(v, std::mt19937{std::random_device{}()}); std::cout << "Contents of the list: "; for(auto n: l) std::cout << n << ' '; std::cout << '\n'; std::cout << "Contents of the list, shuffled: "; for(auto i: v) std::cout << *i << ' '; std::cout << '\n'; }
Possible output:
Contents of the list: -4 -3 -2 -1 0 1 2 3 4 5 Contents of the list, shuffled: 0 -1 3 4 -4 1 -2 -3 2 5
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) |