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std::ranges::generate_random

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
Swap operations
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Generation operations
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(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
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(C++11)
(C++17)
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C library
Numeric operations
Operations on uninitialized memory
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations (on sorted ranges)
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutation operations
Numeric operations
Fold operations
Operations on uninitialized storage
Random number generation
ranges::generate_random
(C++26)
Return types
 
Defined in header <random>
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>>

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>>

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.

1) 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.
3) 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 niebloids, that is:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] Parameters

first, last - iterator-sentinel pair that denotes the range to which random numbers are written
r - 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 <algorithm>
#include <iomanip>
#include <iostream>
#include <random>
 
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

[edit] See also

saves the result of a function in a range
(niebloid)[edit]
specifies that a type qualifies as a uniform random bit generator
(concept) [edit]