GeezerVison is showing doc.rust-lang.org — BufWriter in std::io - Rust Struct BufWriter 1.0.0 · Source pub struct BufWriter<W>{ /* private fields */ }
Expand descriptionWraps 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§
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());
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);
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();
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");
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();
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();
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();
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§
Formats the value using the given formatter. Read more
Executes the destructor for this type. Read more
🔬This is a nightly-only experimental API. (pin_ergonomics #130494) Execute the destructor for this type, but different to Drop::drop, it requires self
to be pinned. Read more
Seek to the offset, in bytes, in the underlying writer.
Seeking always writes out the internal buffer before seeking.
Rewind to the beginning of a stream. Read more
🔬This is a nightly-only experimental API. (seek_stream_len #59359) Returns the length of this stream (in bytes). Read more
Returns the current seek position from the start of the stream. Read more
Seeks relative to the current position. Read more
Writes a buffer into this writer, returning how many bytes were written. Read more
Attempts to write an entire buffer into this writer. Read more
🔬This is a nightly-only experimental API. (can_vector #69941)
Flushes this output stream, ensuring that all intermediately buffered
contents reach their destination. Read more
🔬This is a nightly-only experimental API. (write_all_vectored #70436) Attempts to write multiple buffers into this writer. Read more
Writes a formatted string into this writer, returning any error
encountered. Read more
Creates a “by reference” adapter for this instance of Write. Read moreAuto Trait Implementations§Blanket Implementations§
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
Returns the argument unchanged.
Calls U::from(self).
That is, this conversion is whatever the implementation of
From<T> for U chooses to do.
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion. |