#include <random>
This header adds random number generation facilities and can produce random numbers using generators and distributions.
Generators: Objects that produces a sequence of pseudo-random values uniformly distributed numbers within a specified range of an engine.
Distributions: Objects that transform sequences of numbers generated by a generator into sequences of numbers that follow a specific random variable distribution, such as Uniform, Normal or Binomial.
| Random number engines | Predefined generators |
|---|---|
| linear_congruential_engine | minstd_rand0 minstd_rand |
| mersenne_twister_engine | mt19937 mt19937_64 |
| implements a subtract-with-carry | ranlux24 ranlux48 |
Example: Seed sequence with enough random data to fill the entire mt19937 state
#include <iostream>
#include <random>
#include <array>
#include <algorithm>
#include <functional>
using namespace std;
int main() {
std::array<int, 624> seed;
std::random_device rd;
std::generate_n(seed.data(), seed.size(), std::ref(rd));
std::seed_seq seq(std::begin(seed), std::end(seed));
std::mt19937 gen(seq);
std::uniform_int_distribution<> distr(100, 200); // define the range
cout << distr(gen);
}
Example: Generate random numbers that are within += “range” of “value“
#include <iostream>
#include <random>
using namespace std;
// generate random numbers within +- "range" of "value"
// Note: The output will vary in every run
double generate(double value, double range) {
std::random_device rd; // obtain a random number from hardware
std::mt19937 gen(rd()); // seed the generator
double low = (1 - range) * value; // calculate low range
double high = (1 + range) * value; // calculate high range
std::uniform_int_distribution<> distr(low, high); // define the range
return distr(gen);
}
int main() {
// generate random number whose value lies between += 30% of 100
for (int i = 0; i < 10; i++) cout << generate(100, 0.3) << " ";
return 0;
}99 85 107 82 109 101 129 80 123 115