Rust by Example

read_lines

The method lines() returns an iterator over the lines of a file.

File::open expects a generic, AsRef. That's what read_lines() expects as input.

use std::fs::File;

use std::io::{self, BufRead};

use std::path::Path;

fn main() {

// File hosts must exist in current path before this produces output

if let Ok(lines) = read_lines("./hosts") {

// Consumes the iterator, returns an (Optional) String

for line in lines {

if let Ok(ip) = line {

println!("{}", ip);

}

}

}

}

// The output is wrapped in a Result to allow matching on errors

// Returns an Iterator to the Reader of the lines of the file.

fn read_lines
(filename: P) -> io::Result>>

where P: AsRef, {

let file = File::open(filename)?;

Ok(io::BufReader::new(file).lines())

}

Running this program simply prints the lines individually.

$ echo -e "127.0.0.1\n192.168.0.1\n" > hosts

$ rustc read_lines.rs && ./read_lines

127.0.0.1

192.168.0.1

This process is more efficient than creating a String in memory especially working with larger files.