Generate Random Values

Recipe	Crates	Categories
Generate random numbers
Generate random numbers within a range
Generate random numbers within a given distribution
Generate random values of a custom type
Create random passwords from a set of alphanumeric characters
Create random passwords from a set of user-defined characters

Generate random numbers

Generates random numbers with help of the random-number generator rand::Rng. Each thread has an initialized generator. Integers are uniformly distributed over the range of the type, and floating point numbers are uniformly distributed from 0 up to but not including 1.

use rand::Rng;

fn main() {
    let mut rng = rand::thread_rng();

    // Note: we use a raw identifier to stay compatible with Rust edition 2024.
    // `gen` is a keyword in the 2024 edition.
    let n1: u8 = rng.r#gen();
    let n2: u16 = rng.r#gen();
    println!("Random u8: {}", n1);
    println!("Random u16: {}", n2);
    println!("Random u32: {}", rng.r#gen::<u32>());
    println!("Random i32: {}", rng.r#gen::<i32>());
    println!("Random float: {}", rng.r#gen::<f64>());
}

Generate random numbers within a range

Generates a random value within half-open [0, 10) range (not including 10) with rand::Rng::gen_range⮳ range.

use rand::Rng;

fn main() {
    let mut rng = rand::thread_rng();
    println!("Integer: {}", rng.gen_range(0..10));
    println!("Float: {}", rng.gen_range(0.0..10.0));
}

rand::distributions::uniform::Uniform can obtain values with uniform distribution. This has the same effect, but may be faster when repeatedly generating numbers in the same range.

use rand::distributions::Distribution;
use rand::distributions::Uniform;

fn main() {
    let mut rng = rand::thread_rng();
    let die = Uniform::from(1..7);

    loop {
        let throw = die.sample(&mut rng);
        println!("Roll the die: {}", throw);
        if throw == 6 {
            break;
        }
    }
}

Generate random numbers within a given distribution

By default, random numbers in the rand⮳ crate have uniform distribution⮳. The rand_distr⮳ crate provides other kinds of distributions. To use them, you instantiate a distribution, then sample from that distribution using rand::distributions::Distribution::sample⮳ with help of a random-number generator rand::Rng⮳. The distributions available are documented here⮳. An example using the rand_distr::Normal⮳ distribution is shown below.

use rand::thread_rng;
use rand_distr::Distribution;
use rand_distr::Normal;
use rand_distr::NormalError;

fn main() -> Result<(), NormalError> {
    let mut rng = thread_rng();
    let normal = Normal::new(2.0, 3.0)?;
    let v = normal.sample(&mut rng);
    println!("{} is from a N(2, 9) distribution", v);
    Ok(())
}

Generate random values of a custom type

Randomly generates a tuple (i32, bool, f64) and variable of user defined type Point. Implements the rand::distributions::Distribution⮳ trait on type Point for rand::distributions::Standard⮳ trait in order to allow random generation.

use rand::Rng;
use rand::distributions::Distribution;
use rand::distributions::Standard;

#[derive(Debug)]
#[allow(dead_code)]
struct Point {
    x: i32,
    y: i32,
}

impl Distribution<Point> for Standard {
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Point {
        let (rand_x, rand_y) = rng.r#gen();
        Point {
            x: rand_x,
            y: rand_y,
        }
    }
}

fn main() {
    let mut rng = rand::thread_rng();
    let rand_tuple = rng.r#gen::<(i32, bool, f64)>();
    let rand_point: Point = rng.r#gen();
    println!("Random tuple: {:?}", rand_tuple);
    println!("Random Point: {:?}", rand_point);
}

Create random passwords from a set of alphanumeric characters

Randomly generates a string of given length ASCII characters in the range A-Z, a-z, 0-9, with rand::distributions::Alphanumeric⮳ sample.

use rand::Rng;
use rand::distributions::Alphanumeric;
use rand::thread_rng;

fn main() {
    let rand_string: String = thread_rng()
        .sample_iter(&Alphanumeric)
        .take(30)
        .map(char::from)
        .collect();
    println!("{}", rand_string);
}

Create random passwords from a set of user-defined characters

Randomly generates a string of given length ASCII characters with custom user-defined bytestring, with rand::Rng::gen_range.

fn main() {
    use rand::Rng;
    const CHARSET: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
                            abcdefghijklmnopqrstuvwxyz\
                            0123456789)(*&^%$#@!~";
    const PASSWORD_LEN: usize = 30;
    let mut rng = rand::thread_rng();

    let password: String = (0..PASSWORD_LEN)
        .map(|_| {
            let idx = rng.gen_range(0..CHARSET.len());
            CHARSET[idx] as char
        })
        .collect();

    println!("{:?}", password);
}