1.0.0[][src]Struct std::io::BufReader

pub struct BufReader<R> { /* fields omitted */ }

The BufReader<R> 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<R> performs large, infrequent reads on the underlying Read and maintains an in-memory buffer of the results.

BufReader<R> 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<R> is dropped, the contents of its buffer will be discarded. Creating multiple instances of a BufReader<R> on the same stream can cause data loss. Reading from the underlying reader after unwrapping the BufReader<R> with BufReader::into_inner can also 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>[src]

Important traits for BufReader<R>
pub fn new(inner: R) -> BufReader<R>[src]

Creates a new BufReader<R> 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>[src]

Creates a new BufReader<R> with the specified buffer capacity.

Examples

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(())
}Run

impl<R> BufReader<R>[src]

Important traits for &'_ mut F
pub fn get_ref(&self) -> &R[src]

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 F
pub fn get_mut(&mut self) -> &mut R[src]

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

Important traits for &'_ [u8]
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[src]

Unwraps this BufReader<R>, returning the underlying reader.

Note that any leftover data in the internal buffer is lost. Therefore, a following read from the underlying reader may lead to data loss.

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>[src]

pub fn seek_relative(&mut self, offset: i64) -> Result<()>[src]

🔬 This is a nightly-only experimental API. (bufreader_seek_relative #31100)

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>[src]

impl<R: Seek> Seek for BufReader<R>[src]

fn seek(&mut self, pos: SeekFrom) -> Result<u64>[src]

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<R> 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).

impl<R: Read> BufRead for BufReader<R>[src]

impl<R> Debug for BufReader<R> where
    R: Debug
[src]

Auto Trait Implementations

impl<R> UnwindSafe for BufReader<R> where
    R: UnwindSafe

impl<R> RefUnwindSafe for BufReader<R> where
    R: RefUnwindSafe

impl<R> Unpin for BufReader<R> where
    R: Unpin

impl<R> Send for BufReader<R> where
    R: Send

impl<R> Sync for BufReader<R> where
    R: Sync

Blanket Implementations

impl<T> From<T> for T[src]

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]