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rustformat

Append to formatted output string in rust

I have code like this:

use std::fmt::Write;

fn main() {
    let mut side_str = String::new();
    write!(&mut side_str, "world").unwrap();

    println!(
        "hello_{:?}_",
        format!("{:?}", side_str),
        );
}

I am getting quotes in the output. How do I write it in a concise manner to not have the quotes?

Solution

  • The placeholder {:?} uses the Debug trait to format values. For Strings the debug implementation includes quotes and escape characters. Your code formats the string twice using the Debug trait, so you get two sets of quotation marks.

    world -> "world" -> "\"world\""

    If you do not want any quotes, use {} to format once using the Display trait. If you want a single set of quotes, use {:?} once.

    println!("hello_{}_", side_str); // hello_world_
println!("hello_{:?}_", side_str); // hello_"world"_