pub struct IoBufWriter<W>{ /* private fields */ }
Expand description
?std
Wraps a writer and buffers its output.
Re-exported from std
::io::
BufWriter
→IoBufWriter
.
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 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();
}
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();
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.
Implementations§
Source§impl<W> BufWriter<W>where
W: Write,
impl<W> BufWriter<W>where
W: Write,
1.0.0 · Sourcepub fn new(inner: W) -> BufWriter<W> ⓘ
pub fn new(inner: W) -> BufWriter<W> ⓘ
Creates a new BufWriter<W>
with a default buffer capacity. The default is currently 8 KiB,
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());
1.0.0 · Sourcepub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> ⓘ
pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> ⓘ
Creates a new BufWriter<W>
with at least the specified buffer capacity.
§Examples
Creating a buffer with a buffer of at least 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);
1.0.0 · Sourcepub fn into_inner(self) -> Result<W, IntoInnerError<BufWriter<W>>> ⓘ
pub fn into_inner(self) -> Result<W, IntoInnerError<BufWriter<W>>> ⓘ
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();
1.56.0 · Sourcepub fn into_parts(self) -> (W, Result<Vec<u8>, WriterPanicked>) ⓘ
pub fn into_parts(self) -> (W, Result<Vec<u8>, WriterPanicked>) ⓘ
Disassembles this BufWriter<W>
, returning the underlying writer, and any buffered but
unwritten data.
If the underlying writer panicked, it is not known what portion of the data was written.
In this case, we return WriterPanicked
for the buffered data (from which the buffer
contents can still be recovered).
into_parts
makes no attempt to flush data and cannot fail.
§Examples
use std::io::{BufWriter, Write};
let mut buffer = [0u8; 10];
let mut stream = BufWriter::new(buffer.as_mut());
write!(stream, "too much data").unwrap();
stream.flush().expect_err("it doesn't fit");
let (recovered_writer, buffered_data) = stream.into_parts();
assert_eq!(recovered_writer.len(), 0);
assert_eq!(&buffered_data.unwrap(), b"ata");
Source§impl<W> BufWriter<W>
impl<W> BufWriter<W>
1.0.0 · Sourcepub fn get_ref(&self) -> &W
pub 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();
1.0.0 · Sourcepub fn get_mut(&mut self) -> &mut W
pub 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();
1.37.0 · Sourcepub fn buffer(&self) -> &[u8] ⓘ
pub fn buffer(&self) -> &[u8] ⓘ
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();
1.46.0 · Sourcepub fn capacity(&self) -> usize ⓘ
pub fn capacity(&self) -> usize ⓘ
Returns the number of bytes the internal buffer can hold without flushing.
§Examples
use std::io::BufWriter;
use std::net::TcpStream;
let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
// Check the capacity of the inner buffer
let capacity = buf_writer.capacity();
// Calculate how many bytes can be written without flushing
let without_flush = capacity - buf_writer.buffer().len();
Trait Implementations§
1.0.0 · Source§impl<W> Seek for BufWriter<W>
impl<W> Seek for BufWriter<W>
Source§fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error> ⓘ
fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error> ⓘ
Seek to the offset, in bytes, in the underlying writer.
Seeking always writes out the internal buffer before seeking.
1.55.0 · Source§fn rewind(&mut self) -> Result<(), Error> ⓘ
fn rewind(&mut self) -> Result<(), Error> ⓘ
Source§fn stream_len(&mut self) -> Result<u64, Error> ⓘ
fn stream_len(&mut self) -> Result<u64, Error> ⓘ
seek_stream_len
)1.0.0 · Source§impl<W> Write for BufWriter<W>
impl<W> Write for BufWriter<W>
Source§fn write(&mut self, buf: &[u8]) -> Result<usize, Error> ⓘ
fn write(&mut self, buf: &[u8]) -> Result<usize, Error> ⓘ
Source§fn write_all(&mut self, buf: &[u8]) -> Result<(), Error> ⓘ
fn write_all(&mut self, buf: &[u8]) -> Result<(), Error> ⓘ
Source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
)Source§fn flush(&mut self) -> Result<(), Error> ⓘ
fn flush(&mut self) -> Result<(), Error> ⓘ
Source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error> ⓘ
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error> ⓘ
write_all_vectored
)Auto Trait Implementations§
impl<W> Freeze for BufWriter<W>
impl<W> RefUnwindSafe for BufWriter<W>where
W: RefUnwindSafe + ?Sized,
impl<W> Send for BufWriter<W>
impl<W> Sync for BufWriter<W>
impl<W> Unpin for BufWriter<W>
impl<W> UnwindSafe for BufWriter<W>where
W: UnwindSafe + ?Sized,
Blanket Implementations§
§impl<T> ArchivePointee for T
impl<T> ArchivePointee for T
§type ArchivedMetadata = ()
type ArchivedMetadata = ()
§fn pointer_metadata(
_: &<T as ArchivePointee>::ArchivedMetadata,
) -> <T as Pointee>::Metadata
fn pointer_metadata( _: &<T as ArchivePointee>::ArchivedMetadata, ) -> <T as Pointee>::Metadata
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T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
Source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Source§impl<T> ByteSized for T
impl<T> ByteSized for T
Source§const BYTE_ALIGN: usize = _
const BYTE_ALIGN: usize = _
Source§fn byte_align(&self) -> usize ⓘ
fn byte_align(&self) -> usize ⓘ
Source§fn ptr_size_ratio(&self) -> [usize; 2]
fn ptr_size_ratio(&self) -> [usize; 2]
Source§impl<T, R> Chain<R> for Twhere
T: ?Sized,
impl<T, R> Chain<R> for Twhere
T: ?Sized,
§impl<T> ExecutableCommand for T
impl<T> ExecutableCommand for T
§fn execute(&mut self, command: impl Command) -> Result<&mut T, Error> ⓘ
fn execute(&mut self, command: impl Command) -> Result<&mut T, Error> ⓘ
Executes the given command directly.
The given command its ANSI escape code will be written and flushed onto Self
.
§Arguments
-
The command that you want to execute directly.
§Example
use std::io;
use crossterm::{ExecutableCommand, style::Print};
fn main() -> io::Result<()> {
// will be executed directly
io::stdout()
.execute(Print("sum:\n".to_string()))?
.execute(Print(format!("1 + 1= {} ", 1 + 1)))?;
Ok(())
// ==== Output ====
// sum:
// 1 + 1 = 2
}
Have a look over at the Command API for more details.
§Notes
- In the case of UNIX and Windows 10, ANSI codes are written to the given ‘writer’.
- In case of Windows versions lower than 10, a direct WinAPI call will be made.
The reason for this is that Windows versions lower than 10 do not support ANSI codes,
and can therefore not be written to the given
writer
. Therefore, there is no difference between execute and queue for those old Windows versions.
Source§impl<T> ExtAny for T
impl<T> ExtAny for T
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Self: Sized,
fn as_any_mut(&mut self) -> &mut dyn Anywhere
Self: Sized,
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T: ?Sized,
impl<T> ExtMem for Twhere
T: ?Sized,
Source§const NEEDS_DROP: bool = _
const NEEDS_DROP: bool = _
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fn mem_align_of_val(&self) -> usize ⓘ
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fn mem_size_of_val(&self) -> usize ⓘ
Source§fn mem_needs_drop(&self) -> bool
fn mem_needs_drop(&self) -> bool
true
if dropping values of this type matters. Read moreSource§fn mem_forget(self)where
Self: Sized,
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Self: Sized,
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§fn instrument(self, span: Span) -> Instrumented<Self> ⓘ
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Source§fn into_either(self, into_left: bool) -> Either<Self, Self> ⓘ
fn into_either(self, into_left: bool) -> Either<Self, Self> ⓘ
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if into_left
is true
.
Converts self
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fn into_either_with<F>(self, into_left: F) -> Either<Self, Self> ⓘ
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if into_left(&self)
returns true
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§impl<T, N1, N2> Niching<NichedOption<T, N1>> for N2
impl<T, N1, N2> Niching<NichedOption<T, N1>> for N2
§unsafe fn is_niched(niched: *const NichedOption<T, N1>) -> bool
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§impl<T> QueueableCommand for T
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§fn queue(&mut self, command: impl Command) -> Result<&mut T, Error> ⓘ
fn queue(&mut self, command: impl Command) -> Result<&mut T, Error> ⓘ
Queues the given command for further execution.
Queued commands will be executed in the following cases:
- When
flush
is called manually on the given type implementingio::Write
. - The terminal will
flush
automatically if the buffer is full. - Each line is flushed in case of
stdout
, because it is line buffered.
§Arguments
-
The command that you want to queue for later execution.
§Examples
use std::io::{self, Write};
use crossterm::{QueueableCommand, style::Print};
fn main() -> io::Result<()> {
let mut stdout = io::stdout();
// `Print` will executed executed when `flush` is called.
stdout
.queue(Print("foo 1\n".to_string()))?
.queue(Print("foo 2".to_string()))?;
// some other code (no execution happening here) ...
// when calling `flush` on `stdout`, all commands will be written to the stdout and therefore executed.
stdout.flush()?;
Ok(())
// ==== Output ====
// foo 1
// foo 2
}
Have a look over at the Command API for more details.
§Notes
- In the case of UNIX and Windows 10, ANSI codes are written to the given ‘writer’.
- In case of Windows versions lower than 10, a direct WinAPI call will be made.
The reason for this is that Windows versions lower than 10 do not support ANSI codes,
and can therefore not be written to the given
writer
. Therefore, there is no difference between execute and queue for those old Windows versions.
§impl<W> SynchronizedUpdate for W
impl<W> SynchronizedUpdate for W
§fn sync_update<T>(
&mut self,
operations: impl FnOnce(&mut W) -> T,
) -> Result<T, Error> ⓘ
fn sync_update<T>( &mut self, operations: impl FnOnce(&mut W) -> T, ) -> Result<T, Error> ⓘ
Performs a set of actions within a synchronous update.
Updates will be suspended in the terminal, the function will be executed against self, updates will be resumed, and a flush will be performed.
§Arguments
-
Function
A function that performs the operations that must execute in a synchronized update.
§Examples
use std::io;
use crossterm::{ExecutableCommand, SynchronizedUpdate, style::Print};
fn main() -> io::Result<()> {
let mut stdout = io::stdout();
stdout.sync_update(|stdout| {
stdout.execute(Print("foo 1\n".to_string()))?;
stdout.execute(Print("foo 2".to_string()))?;
// The effects of the print command will not be present in the terminal
// buffer, but not visible in the terminal.
std::io::Result::Ok(())
})?;
// The effects of the commands will be visible.
Ok(())
// ==== Output ====
// foo 1
// foo 2
}
§Notes
This command is performed only using ANSI codes, and will do nothing on terminals that do not support ANSI codes, or this specific extension.
When rendering the screen of the terminal, the Emulator usually iterates through each visible grid cell and renders its current state. With applications updating the screen a at higher frequency this can cause tearing.
This mode attempts to mitigate that.
When the synchronization mode is enabled following render calls will keep rendering the last rendered state. The terminal Emulator keeps processing incoming text and sequences. When the synchronized update mode is disabled again the renderer may fetch the latest screen buffer state again, effectively avoiding the tearing effect by unintentionally rendering in the middle a of an application screen update.