file-read.rs

use std::{
    fs::File,
    str::from_utf8,
    io::{Read, Write},
    os::unix::io::AsRawFd,
};

fn main() -> std::io::Result<()> {
    let mut write_file = File::create("test.txt")?;
    let mut read_file = File::open("test.txt")?;

    assert_ne!(write_file.as_raw_fd(), read_file.as_raw_fd());

    write_file.write_all(b"ABCDEFGHIJKL")?;

    println!("wrote to file");

    loop {
        let mut buffer = [0u8; 4];

        let sz = read_file.read(&mut buffer)?;

        if sz > 0 {
            println!("read() returned {} bytes: {:?}", sz, from_utf8(&buffer[..sz]));
        } else {
            println!("read() returned 0, we're at end of file");
            break;
        }
    }

    write_file.write_all(b"MNOPQRSTUVWXYZ")?;
    println!("wrote more data to the file");

    loop {
        let mut buffer = [0u8; 4];

        let sz = read_file.read(&mut buffer)?;

        if sz > 0 {
            println!("read() returned {} bytes: {:?}", sz, from_utf8(&buffer[..sz]));
        } else {
            println!("read() returned 0, we're at end of file");
            break;
        }
    }

    Ok(())
}