Rust by Example

open

The open static method can be used to open a file in read-only mode.

A File owns a resource, the file descriptor and takes care of closing the file when it is droped.

use std::fs::File;

use std::io::prelude::*;

use std::path::Path;

fn main() {

// Create a path to the desired file

let path = Path::new("hello.txt");

let display = path.display();

// Open the path in read-only mode, returns `io::Result`

let mut file = match File::open(&path) {

Err(why) => panic!("couldn't open {}: {}", display, why),

Ok(file) => file,

};

// Read the file contents into a string, returns `io::Result`

let mut s = String::new();

match file.read_to_string(&mut s) {

Err(why) => panic!("couldn't read {}: {}", display, why),

Ok(_) => print!("{} contains:\n{}", display, s),

}

// `file` goes out of scope, and the "hello.txt" file gets closed

}

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Here's the expected successful output:

$ echo "Hello World!" > hello.txt

$ rustc open.rs && ./open

hello.txt contains:

Hello World!

(You are encouraged to test the previous example under different failure conditions: hello.txt doesn't exist, or hello.txt is not readable, etc.)