1.0.0[−][src]Struct std::io::BufWriter
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<W>
keeps an in-memory buffer of data and writes it to an underlying
writer in large, infrequent batches.
BufWriter<W>
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>
.
It is critical to call flush
before BufWriter<W>
is dropped. Though
dropping will attempt to flush the the contents of the buffer, any errors
that happen in the process of dropping will be ignored. Calling ['flush']
ensures that the buffer is empty and thus dropping will not even attempt
file operations.
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<W>
:
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(); } stream.flush().unwrap();Run
By wrapping the stream with a BufWriter<W>
, these ten writes are all grouped
together by the buffer and will all be written out in one system call when
the stream
is flushed.
Methods
impl<W: Write> BufWriter<W>
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ⓘImportant traits for BufWriter<W>pub fn new(inner: W) -> BufWriter<W>
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Creates a new BufWriter<W>
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>pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W>
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Creates a new BufWriter<W>
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 Fpub fn get_ref(&self) -> &W
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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 Fpub fn get_mut(&mut self) -> &mut W
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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
pub fn buffer(&self) -> &[u8]
1.37.0[src]
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
pub fn into_inner(self) -> Result<W, IntoInnerError<BufWriter<W>>>
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Unwraps this BufWriter<W>
, 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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fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
impl<W: Write + Seek> Seek for BufWriter<W>
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fn seek(&mut self, pos: SeekFrom) -> Result<u64>
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Seek to the offset, in bytes, in the underlying writer.
Seeking always writes out the internal buffer before seeking.
fn stream_len(&mut self) -> Result<u64>
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fn stream_position(&mut self) -> Result<u64>
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impl<W: Write> Drop for BufWriter<W>
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impl<W: Write> Debug for BufWriter<W> where
W: Debug,
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W: Debug,
Auto Trait Implementations
impl<W> UnwindSafe for BufWriter<W> where
W: UnwindSafe,
W: UnwindSafe,
impl<W> RefUnwindSafe for BufWriter<W> where
W: RefUnwindSafe,
W: RefUnwindSafe,
impl<W> Unpin for BufWriter<W> where
W: Unpin,
W: Unpin,
impl<W> Send for BufWriter<W> where
W: Send,
W: Send,
impl<W> Sync for BufWriter<W> where
W: Sync,
W: Sync,
Blanket Implementations
impl<T> From<T> for T
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impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
ⓘImportant traits for &'_ mut Ffn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,