Module io

Traits, helpers, and type definitions for core I/O functionality.

The std::io module contains a number of common things you’ll need when doing input and output. The most core part of this module is the Read and Write traits, which provide the most general interface for reading and writing input and output.

Read and Write

Because they are traits, Read and Write are implemented by a number of other types, and you can implement them for your types too. As such, you’ll see a few different types of I/O throughout the documentation in this module: Files, TcpStreams, and sometimes even Vec<T>s. For example, Read adds a read method, which we can use on Files:

use std::io;
use std::io::prelude::*;
use std::fs::File;

fn main() -> io::Result<()> {
    let mut f = File::open("foo.txt")?;
    let mut buffer = [0; 10];

    // read up to 10 bytes
    let n = f.read(&mut buffer)?;

    println!("The bytes: {:?}", &buffer[..n]);
    Ok(())
}

Read and Write are so important, implementors of the two traits have a nickname: readers and writers. So you’ll sometimes see ‘a reader’ instead of ‘a type that implements the Read trait’. Much easier!

Seek and BufRead

Beyond that, there are two important traits that are provided: Seek and BufRead. Both of these build on top of a reader to control how the reading happens. Seek lets you control where the next byte is coming from: