Struct std::io::BufWriter

pub struct BufWriter<W: Write> {
    // some fields omitted
}

Wraps a writer and buffers its output.

It can be excessively inefficient to work directly with something that implements Write. For example, every call to write on TcpStream results in a system call. A BufWriter keeps an in-memory buffer of data and writes it to an underlying writer in large, infrequent batches.

The buffer will be written out when the writer is dropped.

Examples

Let's write the numbers one through ten to a TcpStream:

fn main() { use std::io::prelude::*; use std::net::TcpStream; let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap(); for i in 1..10 { stream.write(&[i]).unwrap(); } }

use std::io::prelude::*;
use std::net::TcpStream;

let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap();

for i in 1..10 {
    stream.write(&[i]).unwrap();
}

Because we're not buffering, we write each one in turn, incurring the overhead of a system call per byte written. We can fix this with a BufWriter:

fn main() { use std::io::prelude::*; use std::io::BufWriter; use std::net::TcpStream; let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); for i in 1..10 { stream.write(&[i]).unwrap(); } }

use std::io::prelude::*;
use std::io::BufWriter;
use std::net::TcpStream;

let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

for i in 1..10 {
    stream.write(&[i]).unwrap();
}

By wrapping the stream with a BufWriter, these ten writes are all grouped together by the buffer, and will all be written out in one system call when the stream is dropped.

Methods

impl<W: Write> BufWriter<W>

fn new(inner: W) -> BufWriter<W>

Creates a new BufWriter with a default buffer capacity.

Examples

fn main() { use std::io::BufWriter; use std::net::TcpStream; let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); }

use std::io::BufWriter;
use std::net::TcpStream;

let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

fn with_capacity(cap: usize, inner: W) -> BufWriter<W>

Creates a new BufWriter with the specified buffer capacity.

Examples

Creating a buffer with a buffer of a hundred bytes.

fn main() { use std::io::BufWriter; use std::net::TcpStream; let stream = TcpStream::connect("127.0.0.1:34254").unwrap(); let mut buffer = BufWriter::with_capacity(100, stream); }

use std::io::BufWriter;
use std::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
let mut buffer = BufWriter::with_capacity(100, stream);

fn get_ref(&self) -> &W

Gets a reference to the underlying writer.

Examples

fn main() { use std::io::BufWriter; use std::net::TcpStream; let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); // we can use reference just like buffer let reference = buffer.get_ref(); }

use std::io::BufWriter;
use std::net::TcpStream;

let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

// we can use reference just like buffer
let reference = buffer.get_ref();

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

Gets a mutable reference to the underlying writer.

It is inadvisable to directly write to the underlying writer.

Examples

fn main() { use std::io::BufWriter; use std::net::TcpStream; let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); // we can use reference just like buffer let reference = buffer.get_mut(); }

use std::io::BufWriter;
use std::net::TcpStream;

let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

// we can use reference just like buffer
let reference = buffer.get_mut();

fn into_inner(self) -> Result<W, IntoInnerError<BufWriter<W>>>

Unwraps this BufWriter, returning the underlying writer.

The buffer is written out before returning the writer.

Examples

fn main() { use std::io::BufWriter; use std::net::TcpStream; let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); // unwrap the TcpStream and flush the buffer let stream = buffer.into_inner().unwrap(); }

use std::io::BufWriter;
use std::net::TcpStream;

let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

// unwrap the TcpStream and flush the buffer
let stream = buffer.into_inner().unwrap();

Trait Implementations

impl<W: Write> Write for BufWriter<W>

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

fn flush(&mut self) -> Result<()>

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

fn write_fmt(&mut self, fmt: Arguments) -> Result<()>

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

impl<W: Write> Debug for BufWriter<W> where W: Debug

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

impl<W: Write + Seek> Seek for BufWriter<W>

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

Seek to the offset, in bytes, in the underlying writer.

Seeking always writes out the internal buffer before seeking.

impl<W: Write> Drop for BufWriter<W>

fn drop(&mut self)