rand
====
A Rust library for random number generators and other randomness functionality.
[](https://travis-ci.org/rust-lang-nursery/rand)
[](https://ci.appveyor.com/project/alexcrichton/rand)
[Documentation](https://docs.rs/rand)
## Usage
Add this to your `Cargo.toml`:
```toml
[dependencies]
rand = "0.4"
```
and this to your crate root:
```rust
extern crate rand;
```
### Versions
The `rand` crate has been at version `0.3` since March 2015. If you wish to
avoid all breaking changes you may wish to stick with this version.
Version `0.4`was released in December 2017. It contains almost no breaking
changes since the `0.3` series, but nevertheless (will) contain a significant
amount of new code, including a new "external" entropy source (`JitterRng`),
`no_std` support, and significant performance improvements for the ISAAC random
number generators.
## Examples
There is built-in support for a random number generator (RNG) associated with each thread stored in thread-local storage. This RNG can be accessed via thread_rng, or used implicitly via random. This RNG is normally randomly seeded from an operating-system source of randomness, e.g. /dev/urandom on Unix systems, and will automatically reseed itself from this source after generating 32 KiB of random data.
```rust
let tuple = rand::random::<(f64, char)>();
println!("{:?}", tuple)
```
```rust
use rand::Rng;
let mut rng = rand::thread_rng();
if rng.gen() { // random bool
println!("i32: {}, u32: {}", rng.gen::<i32>(), rng.gen::<u32>())
}
```
It is also possible to use other RNG types, which have a similar interface. The following uses the "ChaCha" algorithm instead of the default.
```rust
use rand::{Rng, ChaChaRng};
let mut rng = rand::ChaChaRng::new_unseeded();
println!("i32: {}, u32: {}", rng.gen::<i32>(), rng.gen::<u32>())
```
## Features
By default, `rand` is built with all stable features available. The following
optional features are available:
- `i128_support` enables support for generating `u128` and `i128` values
- `nightly` enables all unstable features (`i128_support`)
- `std` enabled by default; by setting "default-features = false" `no_std`
mode is activated; this removes features depending on `std` functionality:
- `OsRng` is entirely unavailable
- `JitterRng` code is still present, but a nanosecond timer must be
provided via `JitterRng::new_with_timer`
- Since no external entropy is available, it is not possible to create
generators with fresh seeds (user must provide entropy)
- `thread_rng`, `weak_rng` and `random` are all disabled
- exponential, normal and gamma type distributions are unavailable
since `exp` and `log` functions are not provided in `core`
- any code requiring `Vec` or `Box`
- `alloc` can be used instead of `std` to provide `Vec` and `Box`
## Testing
Unfortunately, `cargo test` does not test everything. The following tests are
recommended:
```
# Basic tests for rand and sub-crates
cargo test --all
# Test no_std support (build only since nearly all tests require std)
cargo build --all --no-default-features
# Test 128-bit support (requires nightly)
cargo test --all --features nightly
# Benchmarks (requires nightly)
cargo bench
# or just to test the benchmark code:
cargo test --benches
```
# `derive(Rand)`
You can derive the `Rand` trait for your custom type via the `#[derive(Rand)]`
directive. To use this first add this to your Cargo.toml:
```toml
rand = "0.4"
rand_derive = "0.3"
```
Next in your crate:
```rust
extern crate rand;
#[macro_use]
extern crate rand_derive;
#[derive(Rand, Debug)]
struct MyStruct {
a: i32,
b: u32,
}
fn main() {
println!("{:?}", rand::random::<MyStruct>());
}
```
# License
`rand` is primarily distributed under the terms of both the MIT
license and the Apache License (Version 2.0).
See LICENSE-APACHE, and LICENSE-MIT for details.