open - Rust By Example
Description: Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries.

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# `open`

The `open` function 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 `drop`ed.

    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<File>`
        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<usize>`
        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
    }

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.)