Practical Rust

File I/O

Write, Read, Parse

Standard-library file functions write and read text. The example writes a number, reads it back, and parses it.

Program

Play the program to round-trip a number through a temporary file.

file_io.rs
Replay: real traced execution (multi-file project)
use std::fs;

fn main() {
    let path = std::env::temp_dir().join(format!("egtry_rust_{}.txt", std::process::id()));
    fs::write(&path, "42\n").unwrap();
    let contents = fs::read_to_string(&path).unwrap();
    let number: i32 = contents.trim().parse().unwrap();
    fs::remove_file(&path).unwrap();
    println!("{}", number * 2);
}

  1. path ← "/tmp/⟨tmp A⟩.txt", contents ← "42\n", number ← 42

    3fn main() {4    let pat→ "/tmp/⟨tmp A⟩.txt"h = std::env::temp_dir().join(format!("egtry_rust_{}.txt", std::process::id()));5    fs::write(&pat"/tmp/⟨tmp A⟩.txt"h, "42\n").unwrap();6    let content→ "42\n"s = fs::read_to_string(&pat"/tmp/⟨tmp A⟩.txt"h).unwrap();7    let numbe→ 42r: i32 = contents.trim().parse().unwrap();8    fs::remove_file(&pat"/tmp/⟨tmp A⟩.txt"h).unwrap();9    println!("{}", number * 2);10}
    output84
fs::write `fs::write` saves text to a file path.
read_to_string `fs::read_to_string` loads the file back as text.
parse `trim().parse()` converts the text to a number.