pub struct BufReader<R> { /* fields omitted */ }
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>
.
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(())
}
Creates a new BufReader
with a default buffer capacity. The default is currently 8 KB,
but may change in the future.
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(())
}
Creates a new BufReader
with the specified buffer capacity.
Creating a buffer with ten bytes of capacity:
use std::io::BufReader;
use std::fs::File;
fn main() -> std::io::Result<()> {
let f = File::open("log.txt")?;
let reader = BufReader::with_capacity(10, f);
Ok(())
}
Gets a reference to the underlying reader.
It is inadvisable to directly read from the underlying reader.
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(())
}
Gets a mutable reference to the underlying reader.
It is inadvisable to directly read from the underlying reader.
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(())
}
🔬 This is a nightly-only experimental API. (bufreader_buffer
)
Returns a reference to the internally buffered data.
Unlike fill_buf
, this will not attempt to fill the buffer if it is empty.
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(())
}
Unwraps this BufReader
, returning the underlying reader.
Note that any leftover data in the internal buffer is lost.
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(())
}
🔬 This is a nightly-only experimental API. (bufreader_seek_relative
)
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.
Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty. Read more
Tells this buffer that amt
bytes have been consumed from the buffer, so they should no longer be returned in calls to read
. Read more
Read all bytes into buf
until the delimiter byte
or EOF is reached. Read more
Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer. Read more
Returns an iterator over the contents of this reader split on the byte byte
. Read more
Returns an iterator over the lines of this reader. Read more
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)
.
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
🔬 This is a nightly-only experimental API. (read_initializer
)
Determines if this Read
er can work with buffers of uninitialized memory. Read more
Read all bytes until EOF in this source, placing them into buf
. Read more
Read all bytes until EOF in this source, appending them to buf
. Read more
Read the exact number of bytes required to fill buf
. Read more
Creates a "by reference" adaptor for this instance of Read
. Read more
Transforms this Read
instance to an [Iterator
] over its bytes. Read more
Creates an adaptor which will chain this stream with another. Read more
Creates an adaptor which will read at most limit
bytes from it. Read more
Formats the value using the given formatter. Read more
type Error = !
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Immutably borrows from an owned value. Read more
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
type Error = <U as TryFrom<T>>::Error
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Mutably borrows from an owned value. Read more