std::ranges::generate_random - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| Call signature | ||
| template< class R, class G > requires ranges::output_range<R, std::invoke_result_t<G&>> && std::uniform_random_bit_generator<std::remove_cvref_t<G>> constexpr ranges::borrowed_iterator_t<R> generate_random( R&& r, G&& g ); | (1) | (since C++26) |
| template< class G, std::output_iterator<std::invoke_result_t<G&>> O, std::sentinel_for<O> S > requires std::uniform_random_bit_generator<std::remove_cvref_t<G>> constexpr O generate_random( O first, S last, G&& g ); | (2) | (since C++26) |
| template< class R, class G, class D > requires ranges::output_range<R, std::invoke_result_t<D&, G&>> && std::invocable<D&, G&> && std::uniform_random_bit_generator<std::remove_cvref_t<G>> && std::is_arithmetic_v<std::invoke_result_t<D&, G&>> constexpr ranges::borrowed_iterator_t<R> generate_random( R&& r, G&& g, D&& d ); | (3) | (since C++26) |
| template< class G, class D, std::output_iterator<std::invoke_result_t<D&, G&>> O, std::sentinel_for<O> S > requires std::invocable<D&, G&> && std::uniform_random_bit_generator<std::remove_cvref_t<G>> && std::is_arithmetic_v<std::invoke_result_t<D&, G&>> constexpr O generate_random( O first, S last, G&& g, D&& d ); | (4) | (since C++26) |
Attempts to generate random numbers with the generate_random member function of the random number generator or the distribution, which is expected to be more efficient. Falls back to element-wise generation if no generate_random member function is available.
Let fallback operation be calling ranges::generate(std::forward<R>(r), std::ref(g)) or ranges::generate(std::forward<R>(r), [&d, &g] { return std::invoke(d, g); }) for (1) or (3) respectively.
- Calls g.generate_random(std::forward<R>(r)) if this expression is well-formed.
Otherwise, let I be std::invoke_result_t<G&>. If R models sized_range, fills r with ranges::size(r) values of I by performing an unspecified number of invocations of the form g() or g.generate_random(s), if such an expression is well-formed for a value N and an object s of type std::span<I, N>.
Otherwise, performs the fallback operation.
- Calls d.generate_random(std::forward<R>(r), g) if this expression is well-formed.
Otherwise, let I be std::invoke_result_t<D&, G&>. If R models sized_range, fills r with ranges::size(r) values of type I by performing an unspecified number of invocations of the form std::invoke(d, g) or d.generate_random(s, g), if such an expression is well-formed for a value N and an object s of type std::span<I, N>.
Otherwise, performs the fallback operation.
2,4) Equivalent to (1,3) respectively, where r is obtained from ranges::subrange<O, S>(std::move(first), last).
If the effects of (1) or (3) are not equivalent to those of the corresponding fallback operation, the behavior is undefined.
The value of N can differ between invocations. Implementations may select smaller values for shorter ranges.
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling 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 inhibited.
[edit] Parameters
| first, last | - | the iterator-sentinel pair defining the range of elements to which random numbers are written |
|---|---|---|
| r | - | the range to which random numbers are written |
| g | - | uniform random bit generator |
| d | - | random number distribution object |
[edit] Notes
At the time of the standardization of std::ranges::generate_random, there is no random number generator or distribution in the standard library that provides a generate_random member function.
std::ranges::generate_random can be more efficient when used with a user-defined random number generator that wraps an underlying vectorized API.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
| __cpp_lib_ranges_generate_random | 202403L | (C++26) | std::ranges::generate_random |
[edit] Example
#include #include #include #include int main() { std::default_random_engine eng; std::default_random_engine::result_type rs[16]{}; std::ranges::generate_random(rs, eng); std::cout << std::left; for (int i{}; auto n : rs) std::cout << std::setw(11) << n << (++i % 4 ? ' ' : '\n'); }
Possible output:
16807 282475249 1622650073 984943658 1144108930 470211272 101027544 1457850878 1458777923 2007237709 823564440 1115438165 1784484492 74243042 114807987 1137522503