std::random_device

From cppreference.com
 
 
 
Pseudo-random number generation
Engines and engine adaptors
linear_congruential_engine (C++11)
mersenne_twister_engine (C++11)
subtract_with_carry_engine (C++11)
discard_block_engine (C++11)
independent_bits_engine (C++11)
shuffle_order_engine (C++11)
Generators
random_device (C++11)
Distributions
Uniform distributions
uniform_int_distribution (C++11)
uniform_real_distribution (C++11)
generate_canonical (C++11)
Bernoulli distributions
bernoulli_distribution (C++11)
binomial_distribution (C++11)
negative_binomial_distribution (C++11)
geometric_distribution (C++11)
Poisson distributions
poisson_distribution (C++11)
exponential_distribution (C++11)
gamma_distribution (C++11)
weibull_distribution (C++11)
extreme_value_distribution (C++11)
Normal distributions
normal_distribution (C++11)
lognormal_distribution (C++11)
chi_squared_distribution (C++11)
cauchy_distribution (C++11)
fisher_f_distribution (C++11)
student_t_distribution (C++11)
Sampling distributions
discrete_distribution (C++11)
piecewise_constant_distribution (C++11)
piecewise_linear_distribution (C++11)
Seed Sequences
seed_seq (C++11)
C library
rand
srand
RAND_MAX
 
 
Defined in header <random>
class random_device;
(since C++11)

std::random_device is a uniformly-distributed integer random number generator that produces non-deterministic random numbers.

Note that std::random_device may be implemented in terms of a pseudo-random number engine if a non-deterministic source (e.g. a hardware device) is not available to the implementation.

Contents

[edit] Member types

Member type Definition
result_type unsigned int

[edit] Member functions

Construction
constructs the engine
(public member function)
operator=
(deleted)
the assignment operator is deleted
(public member function)
Generation
advances the engine's state and returns the generated value
(public member function)
Characteristics
obtains the entropy estimate for the non-deterministic random number generator
(public member function)
[static]
gets the smallest possible value in the output range
(public static member function)
[static]
gets the largest possible value in the output range
(public static member function)

[edit] Example

#include <iostream>
#include <string>
#include <map>
#include <random>
 
int main()
{
    std::random_device rd;
    std::map<int, int> hist;
    std::uniform_int_distribution<int> dist(0, 9);
    for (int n = 0; n < 20000; ++n) {
        ++hist[dist(rd)];
    }
    for (auto p : hist) {
        std::cout << p.first << " : " << std::string(p.second/100, '*') << '\n';
    }
}

Possible output:

0 : ********************
1 : *******************
2 : ********************
3 : ********************
4 : ********************
5 : *******************
6 : ********************
7 : ********************
8 : *******************
9 : ********************