2

Code:

use std::io::Read;

fn main() {
  let mut file = std::fs::File::open("numbs").unwrap();
  let mut contents = String::new();
  file.read_to_string(&mut contents).unwrap();
  let mut v: Vec<i32> = Vec::new();
  for s in contents.lines() {
      v.push(s.parse::<i32>().unwrap());
  }
}

Error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: Empty }', src/libcore/result.rs:1165:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
sshashank124
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William Vandrake
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1 Answers1

2

Most likely, you have a trailing newline character \n at the end of your file i.e. an empty last line. You might also have empty lines in the middle of your file.

The easiest way to fix this for your use case is to just ignore empty lines:

for s in contents.lines() {
    if !s.is_empty() {
        v.push(s.parse::<i32>().unwrap());
    }
}

However, it is generally not a good idea to just unwrap a Result especially if you cannot guarantee that it will never panic. A more robust solution is to handle each possible outcome of the Result appropriately. Another advantage of this solution is that it will not just ignore empty lines but also strings that cannot be parsed as an i32. Whether this is what you want or if you wish to handle this error explicitly is up to you. In the following example, we will use if-let to only insert values into the vector if they were successfully parsed as an i32:

for s in contents.lines() {
    if let Ok(i) = s.parse::<i32>() {
        v.push(i);
    }
}

Side Note: You don't need to read the entire file into a string and then parse that line-by-line. Refer to Read large files line by line in Rust to see how to achieve this more idiomatically

Combining the aforementioned point and the use of flatten and flat_map, we can greatly simplify the logic to:

use std::fs::File;
use std::io::{BufRead, BufReader};

fn main() {
    let file = File::open("numbs").unwrap();
    let v: Vec<i32> = BufReader::new(file)
                          .lines()
                          .flatten()                             // gets rid of Err from lines
                          .flat_map(|line| line.parse::<i32>())  // ignores Err variant from Result of str.parse
                          .collect();
}
sshashank124
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