coding-horror/basic-computer-games · error

Failed to get input

Error message

Failed to get input

What it means

This panic is triggered by `.expect("Failed to get input")` on `io::stdin().read_line()` at the very start of Stars' `main()` (line 18), when asking whether the player wants instructions. The `.expect` fires on any I/O-level stdin failure. Note that line 20 (`need_instrut[..1]`) would separately panic on empty input with an index-out-of-bounds, but that is a different error from this `read_line` panic.

Source

Thrown at 82_Stars/rust/src/main.rs:18

use rand::Rng;
use std::io;

fn main() {
    println!(
        "{: >39}\n{: >57}\n\n\n",
        "STARS", "CREATIVE COMPUTING  MORRISTOWN, NEW JERSEY"
    );
    // STARS - PEOPLE'S COMPUTER CENTER, MENLO PARK, CA
    // A IS LIMIT ON NUMBER, M IS NUMBER OF GUESSES
    let a: u32 = 101;
    let m: u32 = 7;
    let mut need_instrut = String::new();

    println!("DO YOU WANT INSTRUCTIONS?");
    io::stdin()
        .read_line(&mut need_instrut)
        .expect("Failed to get input");

    if need_instrut[..1].to_ascii_lowercase().eq("y") {
        println!("I AM THINKING OF A WHOLE NUMBER FROM 1 TO {}", a - 1);
        println!("TRY TO GUESS MY NUMBER.  AFTER YOU GUESS, I");
        println!("WILL TYPE ONE OR MORE STARS (*).  THE MORE");
        println!("STARS I TYPE, THE CLOSER YOU ARE TO MY NUMBER.");
        println!("ONE STAR (*) MEANS FAR AWAY, SEVEN STARS (*******)");
        println!("MEANS REALLY CLOSE!  YOU GET {} GUESSES.\n\n", m);
    }

    loop {
        println!("\nOK, I AM THINKING OF A NUMBER, START GUESSING.\n");
        let rand_number: i32 = rand::thread_rng().gen_range(1..a) as i32; // generates a random number between 1 and 100

        // GUESSING BEGINS, HUMAN GETS M GUESSES
        for i in 0..m {
            let mut guess = String::new();
            println!("YOUR GUESS?");

View on GitHub (pinned to 5301155192)

Solutions

1. Replace `.expect` with a `match` that handles EOF gracefully and defaults to skipping instructions.
2. Guard the `need_instrut[..1]` indexing on line 20 with a length check to prevent the related index-out-of-bounds panic.
3. For non-interactive use, pipe `"n\n"` or `"y\n"` as the first line of input.

Example fix

// before
io::stdin()
    .read_line(&mut need_instrut)
    .expect("Failed to get input");

// after
match io::stdin().read_line(&mut need_instrut) {
    Ok(0) => { println!("No input detected. Starting game without instructions."); }
    Ok(_) => {}
    Err(e) => { eprintln!("Input error: {}", e); return; }
}

// also fix the indexing:
// before: if need_instrut[..1].to_ascii_lowercase().eq("y")
// after:  if need_instrut.trim_start().starts_with('y')

// Pre-check stdin and guard against empty input
use std::io::IsTerminal;
if !io::stdin().is_terminal() {
    eprintln!("Warning: non-interactive stdin.");
}
// After reading, guard the indexing:
if need_instrut.is_empty() { /* skip instructions or default */ }

// Guard the [..1] indexing with a safe check
fn wants_instructions(input: &str) -> bool {
    input.trim_start().to_ascii_lowercase().starts_with('y')
}

match io::stdin().read_line(&mut need_instrut) {
    Ok(0) => { /* skip instructions */ }
    Ok(_) => { /* safe-index with starts_with */ }
    Err(e) => { eprintln!("{}", e); return; }
}

When it happens

Trigger: Stdin returns `Err` or EOF at the instructions prompt. If stdin is closed/redirected, this is the first panic the player hits, before the game even starts. An empty line (just Enter) returns `Ok` with content `"\n"`, so it does *not* trigger this panic — instead it triggers the `[..1]` indexing panic on line 20.

Common situations: Non-interactive execution. Running in CI. Stdin redirected from `/dev/null`. No TTY allocated (Docker without `-it`). Process spawned by a GUI without stdin wiring.

Related errors

• Failed to read the line
• No valid input
• CANNOT READ INPUT!
• CANNOT READ INPUT!
• Failed to read line.

AI-assisted analysis of coding-horror/basic-computer-games@5301155192 (2026-08-13). Data as JSON: /api/errors/f2199b075f413ef7. Report an issue: GitHub.