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How can I read a single line from stdin?

 4 years ago
source link: https://stackoverflow.com/questions/30186037/how-can-i-read-a-single-line-from-stdin
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How can I read a single line from stdin?

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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

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