Struct std::io::BufReader

pub struct BufReader<R> {
    // some fields omitted
}

The BufReader struct adds buffering to any reader.

It can be excessively inefficient to work directly with a Read instance. For example, every call to read on TcpStream results in a system call. A BufReader performs large, infrequent reads on the underlying Read and maintains an in-memory buffer of the results.

Examples

fn main() { use std::io::prelude::*; use std::io::BufReader; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::open("log.txt")); let mut reader = BufReader::new(f); let mut line = String::new(); let len = try!(reader.read_line(&mut line)); println!("First line is {} bytes long", len); Ok(()) } }

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

let mut f = try!(File::open("log.txt"));
let mut reader = BufReader::new(f);

let mut line = String::new();
let len = try!(reader.read_line(&mut line));
println!("First line is {} bytes long", len);

Methods

impl<R: Read> BufReader<R>

fn new(inner: R) -> BufReader<R>

Creates a new BufReader with a default buffer capacity.

Examples

fn main() { use std::io::BufReader; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::open("log.txt")); let mut reader = BufReader::new(f); Ok(()) } }

use std::io::BufReader;
use std::fs::File;

let mut f = try!(File::open("log.txt"));
let mut reader = BufReader::new(f);

fn with_capacity(cap: usize, inner: R) -> BufReader<R>

Creates a new BufReader with the specified buffer capacity.

Examples

Creating a buffer with ten bytes of capacity:

fn main() { use std::io::BufReader; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::open("log.txt")); let mut reader = BufReader::with_capacity(10, f); Ok(()) } }

use std::io::BufReader;
use std::fs::File;

let mut f = try!(File::open("log.txt"));
let mut reader = BufReader::with_capacity(10, f);

fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

Examples

fn main() { use std::io::BufReader; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f1 = try!(File::open("log.txt")); let mut reader = BufReader::new(f1); let f2 = reader.get_ref(); Ok(()) } }

use std::io::BufReader;
use std::fs::File;

let mut f1 = try!(File::open("log.txt"));
let mut reader = BufReader::new(f1);

let f2 = reader.get_ref();

fn get_mut(&mut self) -> &mut R

Gets a mutable reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

Examples

fn main() { use std::io::BufReader; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f1 = try!(File::open("log.txt")); let mut reader = BufReader::new(f1); let f2 = reader.get_mut(); Ok(()) } }

use std::io::BufReader;
use std::fs::File;

let mut f1 = try!(File::open("log.txt"));
let mut reader = BufReader::new(f1);

let f2 = reader.get_mut();

fn into_inner(self) -> R

Unwraps this BufReader, returning the underlying reader.

Note that any leftover data in the internal buffer is lost.

Examples

fn main() { use std::io::BufReader; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f1 = try!(File::open("log.txt")); let mut reader = BufReader::new(f1); let f2 = reader.into_inner(); Ok(()) } }

use std::io::BufReader;
use std::fs::File;

let mut f1 = try!(File::open("log.txt"));
let mut reader = BufReader::new(f1);

let f2 = reader.into_inner();

Trait Implementations

impl<R: Read> Read for BufReader<R>

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>

Read all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize>

Read all bytes until EOF in this source, placing them into buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>

Read the exact number of bytes required to fill buf.

fn by_ref(&mut self) -> &mut Self where Self: Sized

Creates a "by reference" adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self> where Self: Sized

Transforms this Read instance to an Iterator over its bytes.

fn chars(self) -> Chars<Self> where Self: Sized

Transforms this Read instance to an Iterator over chars.

fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized

Creates an adaptor which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self> where Self: Sized

Creates an adaptor which will read at most limit bytes from it.

impl<R: Read> BufRead for BufReader<R>

fn fill_buf(&mut self) -> Result<&[u8]>

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

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.

fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>

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

fn read_line(&mut self, buf: &mut String) -> Result<usize>

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

fn split(self, byte: u8) -> Split<Self> where Self: Sized

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

fn lines(self) -> Lines<Self> where Self: Sized

Returns an iterator over the lines of this reader.

impl<R> Debug for BufReader<R> where R: Debug

fn fmt(&self, fmt: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<R: Seek> Seek for BufReader<R>

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Seek to an offset, in bytes, in the underlying reader.

The position used for seeking with SeekFrom::Current(_) is the position the underlying reader would be at if the BufReader had no internal buffer.

Seeking always discards the internal buffer, even if the seek position would otherwise fall within it. This guarantees that calling .unwrap() immediately after a seek yields the underlying reader at the same position.

See std::io::Seek for more details.

Note: In the edge case where you're seeking with SeekFrom::Current(n) where n minus the internal buffer length underflows an i64, two seeks will be performed instead of one. If the second seek returns Err, the underlying reader will be left at the same position it would have if you seeked to SeekFrom::Current(0).