src/std_misc/file/open.md

# `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.

```rust,editable,ignore
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:

```shell
$ 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.)