std::io::BufRead - Rust (original) (raw)

Trait std::io::BufRead1.0.0 [−] [src]

pub trait BufRead: Read { fn fill_buf(&mut self) -> Result<&u8[]>; fn consume(&mut self, amt: usize);

fn [read_until](#method.read%5Funtil)(&mut self, byte: [u8](../primitive.u8.html), buf: &mut [Vec](../../std/vec/struct.Vec.html "struct std::vec::Vec")<[u8](../primitive.u8.html)>) -> [Result](../../std/io/type.Result.html "type std::io::Result")<[usize](../primitive.usize.html)> { ... }
fn [read_line](#method.read%5Fline)(&mut self, buf: &mut [String](../../std/string/struct.String.html "struct std:🧵:String")) -> [Result](../../std/io/type.Result.html "type std::io::Result")<[usize](../primitive.usize.html)> { ... }
fn [split](#method.split)(self, byte: [u8](../primitive.u8.html)) -> [Split](../../std/io/struct.Split.html "struct std::io::Split")<Self>

    where
        Self: Sized, { ... } fn lines(self) -> Lines
    where
        Self: Sized, { ... } }

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 aread_line method as well as a lines iterator.

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()); }Run

If you have something that implements Read, you can use the BufReadertype 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;

let f = File::open("foo.txt")?; let f = BufReader::new(f);

for line in f.lines() { println!("{}", line.unwrap()); } Run

fn [fill_buf](#tymethod.fill%5Fbuf)(&mut self) -> [Result](../../std/io/type.Result.html "type std::io::Result")<[&[](../primitive.slice.html)[u8](../primitive.u8.html)[]](../primitive.slice.html)>

Fills the internal buffer of this object, returning the buffer contents.

This function is a lower-level call. It needs to be paired with theconsume 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.

This function will return an I/O error if the underlying reader was read, but returned an error.

A locked standard input implements BufRead:

use std::io; use std::io::prelude::*;

let stdin = io::stdin(); let mut stdin = stdin.lock();

let length = { let buffer = stdin.fill_buf().unwrap();

println!("{:?}", buffer);

buffer.len()

};

stdin.consume(length);Run

fn [consume](#tymethod.consume)(&mut self, amt: [usize](../primitive.usize.html))

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 thefill_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 iffill_buf isn't called before calling it.

The amt must be <= the number of bytes in the buffer returned byfill_buf.

Since consume() is meant to be used with fill_buf, that method's example includes an example of consume().

fn [read_until](#method.read%5Funtil)(&mut self, byte: [u8](../primitive.u8.html), buf: &mut [Vec](../../std/vec/struct.Vec.html "struct std::vec::Vec")<[u8](../primitive.u8.html)>) -> [Result](../../std/io/type.Result.html "type std::io::Result")<[usize](../primitive.usize.html)>

Read all bytes into buf until the delimiter byte or EOF is reached.

This function will read bytes from the underlying stream until the delimiter or EOF is found. Once found, all bytes up to, and including, the delimiter (if found) will be appended to buf.

If successful, this function will return the total number of bytes read.

An empty buffer returned indicates that the stream has reached EOF.

This function will ignore all instances of ErrorKind::Interrupted and will otherwise return any errors returned by fill_buf.

If an I/O error is encountered then all bytes read so far will be present in buf and its length will have been adjusted appropriately.

std::io::Cursor is a type that implements BufRead. In this example, we use Cursor to read all the bytes in a byte slice in hyphen delimited segments:

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

let mut cursor = io::Cursor::new(b"lorem-ipsum"); let mut buf = vec![];

let num_bytes = cursor.read_until(b'-', &mut buf) .expect("reading from cursor won't fail"); assert_eq!(num_bytes, 6); assert_eq!(buf, b"lorem-"); buf.clear();

let num_bytes = cursor.read_until(b'-', &mut buf) .expect("reading from cursor won't fail"); assert_eq!(num_bytes, 5); assert_eq!(buf, b"ipsum"); buf.clear();

let num_bytes = cursor.read_until(b'-', &mut buf) .expect("reading from cursor won't fail"); assert_eq!(num_bytes, 0); assert_eq!(buf, b"");Run

fn [read_line](#method.read%5Fline)(&mut self, buf: &mut [String](../../std/string/struct.String.html "struct std:🧵:String")) -> [Result](../../std/io/type.Result.html "type std::io::Result")<[usize](../primitive.usize.html)>

Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer.

This function will read bytes from the underlying stream until the newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes up to, and including, the delimiter (if found) will be appended tobuf.

If successful, this function will return the total number of bytes read.

An empty buffer returned indicates that the stream has reached EOF.

This function has the same error semantics as [read_until] and will also return an error if the read bytes are not valid UTF-8. If an I/O error is encountered then buf may contain some bytes already read in the event that all data read so far was valid UTF-8.

std::io::Cursor is a type that implements BufRead. In this example, we use Cursor to read all the lines in a byte slice:

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

let mut cursor = io::Cursor::new(b"foo\nbar"); let mut buf = String::new();

let num_bytes = cursor.read_line(&mut buf) .expect("reading from cursor won't fail"); assert_eq!(num_bytes, 4); assert_eq!(buf, "foo\n"); buf.clear();

let num_bytes = cursor.read_line(&mut buf) .expect("reading from cursor won't fail"); assert_eq!(num_bytes, 3); assert_eq!(buf, "bar"); buf.clear();

let num_bytes = cursor.read_line(&mut buf) .expect("reading from cursor won't fail"); assert_eq!(num_bytes, 0); assert_eq!(buf, "");Run

ⓘImportant traits for Split

`fn split(self, byte: u8) -> Split where

Self: Sized, `

Returns an iterator over the contents of this reader split on the bytebyte.

The iterator returned from this function will return instances ofio::Result<Vec>. Each vector returned will not have the delimiter byte at the end.

This function will yield errors whenever read_until would have also yielded an error.

std::io::Cursor is a type that implements BufRead. In this example, we use Cursor to iterate over all hyphen delimited segments in a byte slice

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

let cursor = io::Cursor::new(b"lorem-ipsum-dolor");

let mut split_iter = cursor.split(b'-').map(|l| l.unwrap()); assert_eq!(split_iter.next(), Some(b"lorem".to_vec())); assert_eq!(split_iter.next(), Some(b"ipsum".to_vec())); assert_eq!(split_iter.next(), Some(b"dolor".to_vec())); assert_eq!(split_iter.next(), None);Run

ⓘImportant traits for Lines

`fn lines(self) -> Lines where

Self: Sized, `

Returns an iterator over the lines of this reader.

The iterator returned from this function will yield instances ofio::Result<String>. Each string returned will not have a newline byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.

std::io::Cursor is a type that implements BufRead. In this example, we use Cursor to iterate over all the lines in a byte slice.

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

let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");

let mut lines_iter = cursor.lines().map(|l| l.unwrap()); assert_eq!(lines_iter.next(), Some(String::from("lorem"))); assert_eq!(lines_iter.next(), Some(String::from("ipsum"))); assert_eq!(lines_iter.next(), Some(String::from("dolor"))); assert_eq!(lines_iter.next(), None);Run

Each line of the iterator has the same error semantics as BufRead::read_line.