pub trait BufRead: Read {
// Required methods
fn fill_buf(&mut self) -> Result<&[u8], Error>;
fn consume(&mut self, amt: usize);
}Expand description
A BufRead is a type of Reader which has an internal buffer, allowing it
to perform extra ways of reading.
For example, reading line-by-line is inefficient without using a buffer, so
if you want to read by line, you’ll need BufRead, which includes a
read_line method as well as a lines iterator.
§Examples
A locked standard input implements BufRead:
use std::io;
use std::io::prelude::*;
let stdin = io::stdin();
for line in stdin.lock().lines() {
println!("{}", line.unwrap());
}If you have something that implements Read, you can use the [BufReader
type][BufReader] to turn it into a BufRead.
For example, File implements Read, but not BufRead.
[BufReader] to the rescue!
use std::io::{self, BufReader};
use std::io::prelude::*;
use std::fs::File;
fn main() -> io::Result<()> {
let f = File::open("foo.txt")?;
let f = BufReader::new(f);
for line in f.lines() {
println!("{}", line.unwrap());
}
Ok(())
}Required Methods§
sourcefn fill_buf(&mut self) -> Result<&[u8], Error>
fn fill_buf(&mut self) -> Result<&[u8], Error>
Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty.
This function is a lower-level call. It needs to be paired with the
consume method to function properly. When calling this
method, none of the contents will be “read” in the sense that later
calling read may return the same contents. As such, consume must
be called with the number of bytes that are consumed from this buffer to
ensure that the bytes are never returned twice.
An empty buffer returned indicates that the stream has reached EOF.
§Errors
This function will return an I/O error if the underlying reader was read, but returned an error.
§Examples
A locked standard input implements BufRead:
use std::io;
use std::io::prelude::*;
let stdin = io::stdin();
let mut stdin = stdin.lock();
let buffer = stdin.fill_buf().unwrap();
// work with buffer
println!("{:?}", buffer);
// ensure the bytes we worked with aren't returned again later
let length = buffer.len();
stdin.consume(length);sourcefn consume(&mut self, amt: usize)
fn consume(&mut self, amt: usize)
Tells this buffer that amt bytes have been consumed from the buffer,
so they should no longer be returned in calls to read.
This function is a lower-level call. It needs to be paired with the
fill_buf method to function properly. This function does
not perform any I/O, it simply informs this object that some amount of
its buffer, returned from fill_buf, has been consumed and should
no longer be returned. As such, this function may do odd things if
fill_buf isn’t called before calling it.
The amt must be <= the number of bytes in the buffer returned by
fill_buf.
§Examples
Since consume() is meant to be used with fill_buf,
that method’s example includes an example of consume().