1.0.0[−][src]Struct std::io::BufReader
The BufReader
struct adds buffering to any reader.
It can be excessively inefficient to work directly with a Read
instance.
For example, every call to read
on TcpStream
results in a system call. A BufReader
performs large, infrequent reads on
the underlying Read
and maintains an in-memory buffer of the results.
BufReader
can improve the speed of programs that make small and
repeated read calls to the same file or network socket. It does not
help when reading very large amounts at once, or reading just one or a few
times. It also provides no advantage when reading from a source that is
already in memory, like a Vec<u8>
.
When the BufReader
is dropped, the contents of its buffer will be
discarded. Creating multiple instances of a BufReader
on the same
stream can cause data loss.
Examples
use std::io::prelude::*; use std::io::BufReader; use std::fs::File; fn main() -> std::io::Result<()> { let f = File::open("log.txt")?; let mut reader = BufReader::new(f); let mut line = String::new(); let len = reader.read_line(&mut line)?; println!("First line is {} bytes long", len); Ok(()) }Run
Methods
impl<R: Read> BufReader<R>
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ⓘImportant traits for BufReader<R>pub fn new(inner: R) -> BufReader<R>
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Creates a new BufReader
with a default buffer capacity. The default is currently 8 KB,
but may change in the future.
Examples
use std::io::BufReader; use std::fs::File; fn main() -> std::io::Result<()> { let f = File::open("log.txt")?; let reader = BufReader::new(f); Ok(()) }Run
ⓘImportant traits for BufReader<R>pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R>
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impl<R> BufReader<R>
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ⓘImportant traits for &'_ mut Fpub fn get_ref(&self) -> &R
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Gets a reference to the underlying reader.
It is inadvisable to directly read from the underlying reader.
Examples
use std::io::BufReader; use std::fs::File; fn main() -> std::io::Result<()> { let f1 = File::open("log.txt")?; let reader = BufReader::new(f1); let f2 = reader.get_ref(); Ok(()) }Run
ⓘImportant traits for &'_ mut Fpub fn get_mut(&mut self) -> &mut R
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Gets a mutable reference to the underlying reader.
It is inadvisable to directly read from the underlying reader.
Examples
use std::io::BufReader; use std::fs::File; fn main() -> std::io::Result<()> { let f1 = File::open("log.txt")?; let mut reader = BufReader::new(f1); let f2 = reader.get_mut(); Ok(()) }Run
pub fn buffer(&self) -> &[u8]
1.37.0[src]
Returns a reference to the internally buffered data.
Unlike fill_buf
, this will not attempt to fill the buffer if it is empty.
Examples
use std::io::{BufReader, BufRead}; use std::fs::File; fn main() -> std::io::Result<()> { let f = File::open("log.txt")?; let mut reader = BufReader::new(f); assert!(reader.buffer().is_empty()); if reader.fill_buf()?.len() > 0 { assert!(!reader.buffer().is_empty()); } Ok(()) }Run
pub fn into_inner(self) -> R
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Unwraps this BufReader
, returning the underlying reader.
Note that any leftover data in the internal buffer is lost.
Examples
use std::io::BufReader; use std::fs::File; fn main() -> std::io::Result<()> { let f1 = File::open("log.txt")?; let reader = BufReader::new(f1); let f2 = reader.into_inner(); Ok(()) }Run
impl<R: Seek> BufReader<R>
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pub fn seek_relative(&mut self, offset: i64) -> Result<()>
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Seeks relative to the current position. If the new position lies within the buffer, the buffer will not be flushed, allowing for more efficient seeks. This method does not return the location of the underlying reader, so the caller must track this information themselves if it is required.
Trait Implementations
impl<R: Read> Read for BufReader<R>
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fn read(&mut self, buf: &mut [u8]) -> Result<usize>
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fn read_vectored(&mut self, bufs: &mut [IoSliceMut]) -> Result<usize>
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unsafe fn initializer(&self) -> Initializer
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fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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Read all bytes until EOF in this source, placing them into buf
. Read more
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
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Read all bytes until EOF in this source, appending them to buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
1.6.0[src]
Read the exact number of bytes required to fill buf
. Read more
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
Creates a "by reference" adaptor for this instance of Read
. Read more
ⓘImportant traits for Bytes<R>fn bytes(self) -> Bytes<Self> where
Self: Sized,
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Self: Sized,
Transforms this Read
instance to an [Iterator
] over its bytes. Read more
ⓘImportant traits for Chain<T, U>fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
Self: Sized,
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Self: Sized,
Creates an adaptor which will chain this stream with another. Read more
ⓘImportant traits for Take<T>fn take(self, limit: u64) -> Take<Self> where
Self: Sized,
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Self: Sized,
Creates an adaptor which will read at most limit
bytes from it. Read more
impl<R: Seek> Seek for BufReader<R>
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fn seek(&mut self, pos: SeekFrom) -> Result<u64>
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Seek to an offset, in bytes, in the underlying reader.
The position used for seeking with SeekFrom::Current(_)
is the
position the underlying reader would be at if the BufReader
had no
internal buffer.
Seeking always discards the internal buffer, even if the seek position
would otherwise fall within it. This guarantees that calling
.into_inner()
immediately after a seek yields the underlying reader
at the same position.
To seek without discarding the internal buffer, use BufReader::seek_relative
.
See std::io::Seek
for more details.
Note: In the edge case where you're seeking with SeekFrom::Current(n)
where n
minus the internal buffer length overflows an i64
, two
seeks will be performed instead of one. If the second seek returns
Err
, the underlying reader will be left at the same position it would
have if you called seek
with SeekFrom::Current(0)
.
fn stream_len(&mut self) -> Result<u64>
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Returns the length of this stream (in bytes). Read more
fn stream_position(&mut self) -> Result<u64>
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Returns the current seek position from the start of the stream. Read more
impl<R: Read> BufRead for BufReader<R>
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fn fill_buf(&mut self) -> Result<&[u8]>
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fn consume(&mut self, amt: usize)
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fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>
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Read all bytes into buf
until the delimiter byte
or EOF is reached. Read more
fn read_line(&mut self, buf: &mut String) -> Result<usize>
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Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer. Read more
ⓘImportant traits for Split<B>fn split(self, byte: u8) -> Split<Self> where
Self: Sized,
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Self: Sized,
Returns an iterator over the contents of this reader split on the byte byte
. Read more
ⓘImportant traits for Lines<B>fn lines(self) -> Lines<Self> where
Self: Sized,
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Self: Sized,
Returns an iterator over the lines of this reader. Read more
impl<R> Debug for BufReader<R> where
R: Debug,
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R: Debug,
Auto Trait Implementations
Blanket Implementations
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> From<T> for T
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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,