1

How can I read a single line from stdin?

 1 year ago
source link: https://stackoverflow.com/questions/30186037/how-can-i-read-a-single-line-from-stdin
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
How can I read a single line from stdin?

Join Stack Overflow to learn, share knowledge, and build your career.

Asked 6 years ago
Viewed 28k times

I'm asking for the equivalent of fgets() in C.

let line = ...;
println!("You entered: {}", line);

I've read How to read user input in Rust?, but it asks how to read multiple lines; I want only one line.

I also read How do I read a single String from standard input?, but I'm not sure if it behaves like fgets() or sscanf("%s",...).

asked May 12 '15 at 8:51

In How to read user input in Rust? you can see how to iterate over all lines:

use std::io::{self, BufRead};

fn main() {
    let stdin = io::stdin();
    for line in stdin.lock().lines() {
        println!("{}", line.unwrap());
    }
}

You can also manually iterate without a for-loop:

use std::io::{self, BufRead};

fn main() {
    let stdin = io::stdin();
    let mut iterator = stdin.lock().lines();
    let line1 = iterator.next().unwrap().unwrap();
    let line2 = iterator.next().unwrap().unwrap();
}

You cannot write a one-liner to do what you want. But the following reads a single line (and is exactly the same answer as in How do I read a single String from standard input?):

use std::io::{self, BufRead};

fn main() {
    let stdin = io::stdin();
    let line1 = stdin.lock().lines().next().unwrap().unwrap();
}

You can also use the text_io crate for super simple input:

#[macro_use] extern crate text_io;

fn main() {
    // reads until a \n is encountered
    let line: String = read!("{}\n");
}
answered May 12 '15 at 9:15

If you truly want the equivalent to fgets, then @Gerstmann is right, you should use Stdin::read_line. This method accepts a buffer that you have more control of to put the string into:

use std::io::{self, BufRead};

fn main() {
    let mut line = String::new();
    let stdin = io::stdin();
    stdin.lock().read_line(&mut line).unwrap();
    println!("{}", line)
}

Unlike C, you can't accidentally overrun the buffer; it will be automatically resized if the input string is too big.

The answer from @oli_obk - ker is the idiomatic solution you will see most of the time. In it, the string is managed for you, and the interface is much cleaner.

answered May 12 '15 at 12:29

Read a single line from stdin:

    let mut line = String::new();
    std::io::stdin().read_line(&mut line)?; // including '\n'

You may remove '\n' using line.trim_end()

Read until EOF:

    let mut buffer = String::new();
    std::io::stdin().read_to_string(&mut buffer)?;

Using implicit synchronization:

use std::io;
fn main() -> io::Result<()> {
    let mut line = String::new();
    io::stdin().read_line(&mut line)?;

    println!("You entered: {}", line);
    Ok(())
}

Using explicit synchronization:

use std::io::{self, BufRead};

fn main() -> io::Result<()> {
    let stdin = io::stdin();
    let mut handle = stdin.lock();

    let mut line = String::new();
    handle.read_line(&mut line)?;

    println!("You entered: {}", line);
    Ok(())
}

If you interested in the number of bytes e.g. n, use:
let n = handle.read_line(&mut line)?;
or
let n = io::stdin().read_line(&mut line)?;

Try this:

use std::io;
fn main() -> io::Result<()> {
    let mut line = String::new();
    let n = io::stdin().read_line(&mut line)?;

    println!("{} bytes read", n);
    println!("You entered: {}", line);
    Ok(())
}

See doc

answered Oct 13 '19 at 12:22

Your Answer

Sign up or log in

Sign up using Google
Sign up using Facebook
Sign up using Email and Password

Post as a guest

Name
Email

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged rust or ask your own question.


About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK