{"record":{"id":"7f9ef1428effed1a","repo":"coding-horror/basic-computer-games","slug":"failed-to-read-the-line-7f9ef1","errorCode":null,"errorMessage":"Failed to read the line","messagePattern":"Failed to read the line","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"54_Letter/rust/src/main.rs","lineNumber":26,"sourceCode":"        \"LETTER\", \"CREATIVE COMPUTING  MORRISTOWN, NEW JERSEY\"\n    );\n    println!(\"LETTER GUESSING GAME\\n\");\n    println!(\"I'LL THINK OF A LETTER OF THE ALPHABET, A TO Z.\");\n    println!(\"TRY TO GUESS MY LETTER AND I'LL GIVE YOU CLUES\");\n    println!(\"AS TO HOW CLOSE YOU'RE GETTING TO MY LETTER.\");\n\n    loop {\n        let gen_character = rand::thread_rng().gen_range('A'..='Z'); // generates a random character between A and Z\n        let gen_character = String::from(gen_character);\n        println!(\"\\nO.K., I HAVE A LETTER.  START GUESSING.\");\n        for i in 0..999999 {\n            println!(\"\\nWHAT IS YOUR GUESS?\");\n\n            let mut guess = String::new();\n\n            io::stdin()\n                .read_line(&mut guess)\n                .expect(\"Failed to read the line\");\n            println!(\"{}\", gen_character);\n            let guess = guess.trim().to_ascii_uppercase();\n            match guess.cmp(&gen_character) {\n                Ordering::Less => println!(\"\\nTOO LOW.  TRY A HIGHER LETTER.\"),\n                Ordering::Greater => println!(\"\\nTOO HIGH.  TRY A LOWER LETTER.\"),\n                Ordering::Equal => {\n                    println!(\"\\nYOU GOT IT IN {} GUESSES!!\", i + 1);\n                    if i >= 4 {\n                        println!(\"BUT IT SHOULDN'T TAKE MORE THAN 5 GUESSES!\\n\");\n                    } else {\n                        println!(\"{}\", std::iter::repeat(\"💖\").take(15).collect::<String>());\n                        println!(\"GOOD JOB !!!!!\");\n                    }\n                    break;\n                }\n            }\n        }\n        println!(\"\\nLET'S PLAY AGAIN.....\");","sourceCodeStart":8,"sourceCodeEnd":44,"githubUrl":"https://github.com/coding-horror/basic-computer-games/blob/5301155192d91d74d337899cecc59dbda59c4c17/54_Letter/rust/src/main.rs#L8-L44","documentation":"In 54_Letter, inside a loop of up to 999999 guesses, the game reads the player's letter guess via io::stdin().read_line(&mut guess).expect(\"Failed to read the line\"). The guess is trimmed, uppercased, and compared to a random character A-Z. There is no parse step, so the .expect() is the only failure point — an empty or wrong letter is handled by the Ordering comparison, but a stdin I/O failure panics.","triggerScenarios":"The game prompts 'WHAT IS YOUR GUESS?' and stdin returns Err or EOF. Invalid guesses (empty string, multiple characters) are handled by the comparison logic (they'll be Ordering::Less or Greater), but missing input is not.","commonSituations":"Piped input that runs out before the letter is guessed, pressing Ctrl+D at a guess prompt, or CI tests that provide insufficient guesses.","solutions":["Replace .expect() with .unwrap_or_default() so I/O failure yields an empty string, which the Ordering comparison handles as a wrong guess","Use match to detect Ok(0) (EOF) and break the guess loop","Return early from the game on Err"],"exampleFix":"// before\nlet mut guess = String::new();\nio::stdin()\n    .read_line(&mut guess)\n    .expect(\"Failed to read the line\");\nprintln!(\"{}\", gen_character);\n\n// after\nlet mut guess = String::new();\nlet _ = io::stdin().read_line(&mut guess);\nprintln!(\"{}\", gen_character);","handlingStrategy":"fallback","validationCode":null,"typeGuard":null,"tryCatchPattern":"let mut guess = String::new();\nlet _ = io::stdin().read_line(&mut guess);\n// empty string compares as Ordering::Less or Greater,\n// which the existing match handles by re-prompting","preventionTips":["For guess loops with no parse step, let I/O failures produce empty strings that the comparison logic handles as wrong guesses","Use let _ = read_line(...) when the downstream logic is a comparison that naturally handles unexpected values","Test letter-guessing games with truncated input to verify the Ordering comparison path handles empty strings without panicking"],"tags":["rust","stdin","read-line","panic","expect","io-error","eof","interactive","game-loop","cli"],"backgroundTag":null,"analyzedSha":"5301155192d91d74d337899cecc59dbda59c4c17","analyzedAt":"2026-08-13T19:29:00.979Z","schemaVersion":2},"datasetVersion":"2026-08-14T00:17:13.853Z"}