make_a_file.rs

use std::io::prelude::*;
use std::fs::File;

fn main() {
    let mut f = File::create("hello_world.txt").unwrap();
    f.write_all(b"Hello world!");
    let mut f = File::open("hello_world.txt").unwrap();
    let mut s = String::new();
    f.read_to_string(&mut s);
    assert_eq!(s, "Hello world!");
}