1.0.0[][src]Struct std::io::BufWriter

pub struct BufWriter<W: Write> { /* 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.

BufWriter can improve the speed of programs that make small and repeated write calls to the same file or network socket. It does not help when writing very large amounts at once, or writing just one or a few times. It also provides no advantage when writing to a destination that is in memory, like a Vec<u8>.

When the BufWriter is dropped, the contents of its buffer will be written out. However, any errors that happen in the process of flushing the buffer when the writer is dropped will be ignored. Code that wishes to handle such errors must manually call flush before the writer is dropped.

Examples

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

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

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

for i in 0..10 {
    stream.write(&[i+1]).unwrap();
}Run

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:

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 0..10 {
    stream.write(&[i+1]).unwrap();
}Run

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>
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Important traits for BufWriter<W>

Creates a new BufWriter with a default buffer capacity. The default is currently 8 KB, but may change in the future.

Examples

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

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

Important traits for BufWriter<W>

Creates a new BufWriter with the specified buffer capacity.

Examples

Creating a buffer with a buffer of a hundred bytes.

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);Run

Important traits for &'_ mut I

Gets a reference to the underlying writer.

Examples

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();Run

Important traits for &'_ mut I

Gets a mutable reference to the underlying writer.

It is inadvisable to directly write to the underlying writer.

Examples

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();Run

Important traits for &'a [u8]

🔬 This is a nightly-only experimental API. (bufreader_buffer #45323)

Returns a reference to the internally buffered data.

Examples

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

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

// See how many bytes are currently buffered
let bytes_buffered = buf_writer.buffer().len();Run

Unwraps this BufWriter, returning the underlying writer.

The buffer is written out before returning the writer.

Errors

An Err will be returned if an error occurs while flushing the buffer.

Examples

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();Run

Trait Implementations

impl<W: Write> Write for BufWriter<W>
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Attempts to write an entire buffer into this write. Read more

Writes a formatted string into this writer, returning any error encountered. Read more

Important traits for &'_ mut I

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

impl<W: Write + Seek> Seek for BufWriter<W>
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Seek to the offset, in bytes, in the underlying writer.

Seeking always writes out the internal buffer before seeking.

impl<W: Write> Debug for BufWriter<W> where
    W: Debug
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impl<W: Write> Drop for BufWriter<W>
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Auto Trait Implementations

impl<W> Send for BufWriter<W> where
    W: Send

impl<W> Sync for BufWriter<W> where
    W: Sync

Blanket Implementations

impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

impl<T> From for T
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impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

impl<T, U> Into for T where
    U: From<T>, 
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impl<T> Borrow for T where
    T: ?Sized
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impl<T> BorrowMut for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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