std::io::BufWriter - Rust
Description: API documentation for the Rust `BufWriter` struct in crate `std`.
Keywords: rust, rustlang, rust-lang, BufWriter

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

    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.

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 1..10 {
        stream.write(&[i]).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 1..10 {
        stream.write(&[i]).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>`
[src]

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

Creates a new `BufWriter` with a default buffer capacity.

# Examples

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

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

#### `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.

    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

#### `fn get_ref(&self) -> &W`

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

#### `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

    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

#### `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

    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>`
[src]

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

Write a buffer into this object, returning how many bytes were written. Read more

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

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more

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

Attempts to write an entire buffer into this write. Read more

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

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

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

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

### `impl<W: Write> Debug for BufWriter<W> where
W: Debug,`
[src]

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

Formats the value using the given formatter.

### `impl<W: Write + Seek> Seek for BufWriter<W>`
[src]

#### `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>`
[src]

#### `fn drop(&mut self)`

A method called when the value goes out of scope. Read more

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