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

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>.

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>

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>

Creates a new BufReader 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

Important traits for &'a mut I

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 &'a mut I

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 &'a [u8]

🔬 This is a nightly-only experimental API. (bufreader_buffer #45323)

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

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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🔬 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>
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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 #42788)

Determines if this Reader 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

Important traits for &'a mut I

Creates a "by reference" adaptor for this instance of Read. Read more

Important traits for Bytes<R>

Transforms this Read instance to an [Iterator] over its bytes. Read more

Important traits for Chain<T, U>

Creates an adaptor which will chain this stream with another. Read more

Important traits for Take<T>

Creates an adaptor which will read at most limit bytes from it. Read more

impl<R: Read> BufRead for BufReader<R>
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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

Important traits for Split<B>

Returns an iterator over the contents of this reader split on the byte byte. Read more

Important traits for Lines<B>

Returns an iterator over the lines of this reader. Read more

impl<R> Debug for BufReader<R> where
    R: Debug
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Formats the value using the given formatter. Read more

impl<R: Seek> Seek for BufReader<R>
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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 [Seek::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).

Auto Trait Implementations

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

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

Blanket Implementations

impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

impl<T> From for T
[src]

Performs the conversion.

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

🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

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

Performs the conversion.

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

Important traits for &'a mut I

Immutably borrows from an owned value. Read more

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

Important traits for &'a mut I

Mutably borrows from an owned value. Read more

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

🔬 This is a nightly-only experimental API. (get_type_id #27745)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more