std::ranges::generate_random

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

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:

• 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.

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

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

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

Example

Run this code

#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

See also

ranges::generate (C++20)	saves the result of a function in a range (niebloid)
uniform_random_bit_generator (C++20)	specifies that a type qualifies as a uniform random bit generator (concept)