How can I read a single line from stdin?

Question

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",...).

Answer 1

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(); } 

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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"); } 

Answer 2

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.