coding-horror/basic-computer-games · warning

Failed to read line

Error message

Failed to read line

What it means

A panic via .expect("Failed to read line") on io::stdin().read_line() in Blackjack's rules-display function that prints instructions then waits for ENTER to continue. read_line fails only on I/O-level errors (closed stdin, EOF, broken pipe). Because the read result is discarded into a fresh String, any read failure aborts the process at the 'PRESS ENTER TO CONTINUE' pause.

Source

Thrown at 10_Blackjack/rust/src/main.rs:557

    THIS IS THE GAME OF 21. AS MANY AS 7 PLAYERS MAY PLAY THE
    GAME. ON EACH DEAL, BETS WILL BE ASKED FOR, AND THE
    PLAYERS' BETS SHOULD BE TYPED IN. THE CARDS WILL THEN BE
    DEALT, AND EACH PLAYER IN TURN PLAYS HIS HAND. THE
    FIRST RESPONSE SHOULD BE EITHER 'D', INDICATING THAT THE
    PLAYER IS DOUBLING DOWN, 'S', INDICATING THAT HE IS
    STANDING, 'H', INDICATING HE WANTS ANOTHER CARD, OR '/',
    INDICATING THAT HE WANTS TO SPLIT HIS CARDS. AFTER THE
    INITIAL RESPONSE, ALL FURTHER RESPONSES SHOULD BE 'S' OR
    'H', UNLESS THE CARDS WERE SPLIT, IN WHICH CASE DOUBLING
    DOWN IS AGAIN PERMITTED. IN ORDER TO COLLECT FOR
    BLACKJACK, THE INITIAL RESPONSE SHOULD BE 'S'.
    NUMBER OF PLAYERS

    NOTE:'/' (splitting) is not currently implemented, and does nothing

    PRESS ENTER TO CONTINUE
    ");
    io::stdin().read_line(&mut String::new()).expect("Failed to read line");
}

/**
 * gets a usize integer from user input
 */
fn get_number_from_user_input(prompt: &str, min:usize, max:usize) -> usize {
    //input loop
    return loop {
        let mut raw_input = String::new(); // temporary variable for user input that can be parsed later

        //print prompt
        println!("{}", prompt);
        stdout().flush().expect("Failed to flush to stdout.");
        //read user input from standard input, and store it to raw_input
        //raw_input.clear(); //clear input
        io::stdin().read_line(&mut raw_input).expect( "CANNOT READ INPUT!");

        //from input, try to read a number

View on GitHub (pinned to 5301155192)

Solutions

1. Include a trailing newline (ENTER) in piped input for the rules pause.
2. Run interactively.
3. Replace .expect with `let _ = io::stdin().read_line(&mut String::new());` to ignore failure at the continue prompt.

Example fix

// before
io::stdin().read_line(&mut String::new()).expect("Failed to read line");

// after
let _ = io::stdin().read_line(&mut String::new());

// The read result is irrelevant; just ignore it so EOF won't abort.

// Discard the read result for the continue prompt
let _ = io::stdin().read_line(&mut String::new());

When it happens

Trigger: The program prints the rules and waits for ENTER, but stdin is closed or at EOF (piped input exhausted, /dev/null, broken pipe); a non-interactive run that never supplies the ENTER.

Common situations: Piping pre-recorded input that omits the final ENTER; running headless with no TTY; CI that closes stdin after dealing setup lines.

Related errors

• Failed to read the line
• CANNOT READ INPUT!
• closing
• 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/6ead1dcbcdca289a. Report an issue: GitHub.