Error reading from BufReader in nested loops

Question

I am been working on a program in Rust to read individual lines from a local text file, divide the line into a character vector and do some other operations. This is the snippet of my code:

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

fn main() {
 
   // ---------  

    let input_file = File::open("----").unwrap();
    let input_file = BufReader::new(input_file);
    let mut temp2 = String::new();
    let mut counter = 0;

    while counter < 12 {
        for line in input_file.lines() {
            let input_line = line.expect("Failed to read line");
            let temp: Vec = input_line.chars().collect::>();
            temp2.push(temp[counter]);
        }

      //------------


Here is the error message as shown up in Cargo:
error[E0382]: use of moved value: `input_file`
    --> src\main.rs:48:21
     |
42   |     let input_file = BufReader::new(input_file);
     |         ---------- move occurs because `input_file` has type `BufReader`, which does not implement the `Copy` trait
...
48   |         for line in input_file.lines() {
     |                     ^^^^^^^^^^ ------- `input_file` moved due to this method call, in previous iteration of loop        
     |
note: this function takes ownership of the receiver `self`, which moves `input_file`
    --> C:\Users\Gumbi\.rustup	oolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\std\src\io\mod.rs:2258:14 
     |
2258 |     fn lines(self) -> Lines
     |              ^^^^

error[E0382]: borrow of moved value: `temp2`
  --> src\main.rs:51:13
   |
44 |     let mut temp2 = String::new();
   |         --------- move occurs because `temp2` has type `String`, which does not implement the `Copy` trait
...
51 |             temp2.push(temp[counter]);
   |             ^^^^^ value borrowed here after move
...
54 |         let temp3 = most_common_digit(temp2);
   |                                       ----- value moved here, in previous iteration of loop


I know the basics of ownership and borrowing, but I am not able to grasp what is the problem in this code. Could anyone please help me in knowing where I am going wrong?

user_1695172 · Answer

The problem is that input_file is moved inside the while loop scope. Instead use an intermediary &mut that can be dropped in each iteration:

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

fn main() {
    // ---------

    let input_file = File::open("----").unwrap();
    let mut input_file = BufReader::new(input_file);
    let mut temp2 = String::new();
    let mut counter = 0;

    while counter < 12 {
        let mut input_file_ref = &mut input_file;

        for line in input_file_ref.lines() {
            let input_line = line.expect("Failed to read line");
            let temp: Vec = input_line.chars().collect::>();
            temp2.push(temp[counter]);
        }
    }
}


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Error reading from BufReader in nested loops

1 Answers