Rust 1.90.0
1159e78c4

FFI

There is a new edition of the book and this is an old link.

Sometimes, your Rust code may need to interact with code written in another language. To do this, Rust has a keyword, extern, that facilitates creating and using a Foreign Function Interface (FFI).

extern "C" {
    fn abs(input: i32) -> i32;
}

fn main() {
    unsafe {
        println!("Absolute value of -3 according to C: {}", abs(-3));
    }
}

You can find the latest version of this information here