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std::ranges::generate_n(3) C++ Standard Libary std::ranges::generate_n(3) NAME std::ranges::generate_n - std::ranges::generate_n Synopsis Defined in header <algorithm> Call signature template< std::input_or_output_iterator O, std::copy_constructible F > requires std::invocable<F&> && std::indirectly_writable<O, (since C++20) std::invoke_result_t<F&>> constexpr O generate_n( O first, std::iter_difference_t<O> n, F gen ); Assigns the result of successive invocations of the function object gen to each element in the range [first, first + n), if 0 < n. Does nothing oth- erwise. The function-like entities described on this page are niebloids, that is: * Explicit template argument lists cannot be specified when call- ing any of them. * None of them are visible to argument-dependent lookup. * When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is in- hibited. In practice, they may be implemented as function objects, or with special compiler extensions. Parameters first - the beginning of the range of elements to modify n - number of elements to modify gen - the generator function object. Return value Iterator one past the last element assigned if 0 < count, first oth- erwise. Complexity Exactly n invocations of gen() and assignments. Possible implementation struct generate_n_fn { template<std::input_or_output_iterator O, std::copy_constructible F> requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> constexpr O operator()(O first, std::iter_difference_t<O> n, F gen) const { for (; n-- > 0; *first = std::invoke(gen), ++first) {} return first; } }; inline constexpr generate_n_fn generate_n {}; Example // Run this code #include <algorithm> #include <array> #include <iostream> #include <random> #include <string_view> auto dice() { static std::uniform_int_distribution<int> distr {1, 6}; static std::random_device engine; static std::mt19937 noise {engine()}; return distr(noise); } void print(const auto& v, std::string_view comment) { for (int i : v) std::cout << i << ' '; std::cout << '(' << comment << ")\n"; } int main() { std::array<int, 8> v; std::ranges::generate_n(v.begin(), v.size(), dice); print(v, "dice"); std::ranges::generate_n(v.begin(), v.size(), [n {0}] mutable { re- turn n++; }); // same effect as std::iota(v.begin(), v.end(), 0); print(v, "iota"); } Possible output: 5 5 2 2 6 6 3 5 (dice) 0 1 2 3 4 5 6 7 (iota) See also ranges::generate saves the result of a function in a range (C++20) (niebloid) ranges::generate_random fills a range with random numbers from a uniform random bit (C++26) generator (niebloid) ranges::fill assigns a range of elements a certain value (C++20) (niebloid) ranges::fill_n assigns a value to a number of elements (C++20) (niebloid) ranges::transform applies a function to a range of elements (C++20) (niebloid) assigns the results of successive function calls to N generate_n elements in a range (function template) http://cppreference.com 2024.06.10 std::ranges::generate_n(3)
NAME | Synopsis | Parameters | Return value | Complexity | Possible implementation | Example | Possible output: | See also
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