std::random_device

Since C++11

Header: <random>

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

# Declarations

class random_device;

(since C++11)

# Notes

A notable implementation where std::random_device is deterministic in old versions of MinGW-w64 (bug 338, fixed since GCC 9.2). The latest MinGW-w64 versions can be downloaded from GCC with the MCF thread model.

# Example

#include <iostream>
#include <map>
#include <random>
#include <string>
 
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)]; // note: demo only: the performance of many
                          // implementations of random_device degrades sharply
                          // once the entropy pool is exhausted. For practical use
                          // random_device is generally only used to seed
                          // a PRNG such as mt19937
 
    for (auto [x, y] : hist)
        std::cout << x << " : " << std::string(y / 100, '*') << '\n';
}