CODEWITHSUNDEEP
rust
John7867
John7867

Reputation: 103

How do I convert from &alloc::string::String to a string literal?

The title says it all really. I need to convert from &alloc::string::String to a string literal (&str I think) according to the error I am getting when I am trying to write to a file. How do I convert what I have into that?

The overall goal here is to read from one file and line by line append to another.

Full code:

use std::{
    fs::File,
    io::{self, BufRead, BufReader},
    fs::OpenOptions,
    fs::write,
    any::type_name,
    path::Path,
    io::Write,
};

fn type_of<T>(_: T) -> &'static str {
    type_name::<T>()
}

fn main(){
    let inpath = Path::new("tool_output.txt");
    let outpath = Path::new("test_output.txt");
    let indisplay = inpath.display();
    let outdisplay = outpath.display();
    
    let mut infile = match File::open(&inpath) {
        Err(why) => panic!("couldn't open {}: {}", indisplay, why),
        Ok(infile) => infile,
    };

    let mut outfile = match OpenOptions::new().write(true).append(true).open(&outpath) {
    Err(why) => panic!("couldn't open {}: {}", outdisplay, why),
        Ok(outfile) => outfile,
    };

    let reader = BufReader::new(infile);

    for line in reader.lines() {
    let format_line = String::from(line.unwrap()); // <- I thought this would fix the error but it didnt.
    println!("Type = {}", type_of(&format_line));
    let _ = writeln!(outfile, &format_line).expect("Unable to write to file"); <- this is currently causing the error.
    //write("test_output.txt", line.unwrap()).expect("Unable to write to file");
    }
}

error:

error: format argument must be a string literal
  --> text_edit.rs:36:28
   |
36 |     let _ = writeln!(outfile, format_line).expect("Unable to write to file"); 
   |                               ^^^^^^^^^^^
   |

Upvotes: 2

Views: 359

Answers (1)

nrabulinski
nrabulinski

Reputation: 76

A string literal is what it says - a literal so "literal" is a string literal. To use writeln macro to write a string, you have to do writeln!(outfile, "{}", line) and here "{}" is the format string literal. If you’ve ever used println macro, it’s basically that but you specify what stream to print to.

Upvotes: 5

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