Reading a file

Read a file with std::fs::read_to_string.

Reading files

The shortest way to read a whole file as text is std::fs::read_to_string. The file might not exist or might not be UTF-8, so it returns io::Result<String>:

use std::fs;
use std::io;

fn main() -> io::Result<()> {
    let icerik = fs::read_to_string("notlar.txt")?;
    println!("{} satır", icerik.lines().count());
    Ok(())
}

Having main return io::Result<()> lets you use ?; on error the program exits with a message and a non-zero code.

Paths and the temp folder

Relative paths are resolved against the folder where the program runs. To build paths independent of the platform, Path/PathBuf and join are used. In the exercises we'll work in the temp folder:

use std::env;
use std::path::PathBuf;

let yol: PathBuf = env::temp_dir().join("rust_ders.txt");
println!("{}", yol.display());

display() turns the path into a printable form; paths don't always have to be valid UTF-8.

Exercise Count lines

Let main return io::Result<()>. Build the path rust_ders.txt in the temp folder, write "elma\narmut\n" with fs::write, read it with fs::read_to_string and print N satır.

Show example solution

use std::env;
use std::fs;
use std::io;

fn main() -> io::Result<()> {
    let yol = env::temp_dir().join("rust_ders.txt");
    fs::write(&yol, "elma\narmut\n")?;
    let icerik = fs::read_to_string(&yol)?;
    println!("{} satır", icerik.lines().count());
    Ok(())
}

Test yourself

Which is used to read a binary file (like an image)?
- fs::read_to_string
- fs::open_text
- fs::lines
- fs::read → Vec<u8>
Show answer

fs::read → Vec<u8> — read_to_string errors on invalid UTF-8; fs::read is used for raw bytes.

Read it all

let icerik = fs::____("notlar.txt")?;

Show answer

let icerik = fs::read_to_string("notlar.txt")?;

Function and return

fs::read_to_string

io::Result<String>
fs::read

io::Result<Vec<u8>>
env::temp_dir()

PathBuf
yol.display()

Printable path

Next lesson: Writing a file

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies