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Struct std::io::LineWriter

pub struct LineWriter<W: Write> { /* fields omitted */ }

Wraps a writer and buffers output to it, flushing whenever a newline (0x0a, '\n') is detected.

The BufWriter struct wraps a writer and buffers its output. But it only does this batched write when it goes out of scope, or when the internal buffer is full. Sometimes, you'd prefer to write each line as it's completed, rather than the entire buffer at once. Enter LineWriter. It does exactly that.

Like BufWriter, a LineWriter’s buffer will also be flushed when the LineWriter goes out of scope or when its internal buffer is full.

If there's still a partial line in the buffer when the LineWriter is dropped, it will flush those contents.

Examples

We can use LineWriter to write one line at a time, significantly reducing the number of actual writes to the file.

use std::fs::{self, File};
use std::io::prelude::*;
use std::io::LineWriter;

fn main() -> std::io::Result<()> {
    let road_not_taken = b"I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I -
I took the one less traveled by,
And that has made all the difference.";

    let file = File::create("poem.txt")?;
    let mut file = LineWriter::new(file);

    file.write_all(b"I shall be telling this with a sigh")?;

    // No bytes are written until a newline is encountered (or
    // the internal buffer is filled).
    assert_eq!(fs::read_to_string("poem.txt")?, "");
    file.write_all(b"\n")?;
    assert_eq!(
        fs::read_to_string("poem.txt")?,
        "I shall be telling this with a sigh\n",
    );

    // Write the rest of the poem.
    file.write_all(b"Somewhere ages and ages hence:
Two roads diverged in a wood, and I -
I took the one less traveled by,
And that has made all the difference.")?;

    // The last line of the poem doesn't end in a newline, so
    // we have to flush or drop the `LineWriter` to finish
    // writing.
    file.flush()?;

    // Confirm the whole poem was written.
    assert_eq!(fs::read("poem.txt")?, &road_not_taken[..]);
    Ok(())
}

Methods

impl<W: Write> LineWriter<W>[src]

pub fn new(inner: W) -> LineWriter<W>[src]

ⓘImportant traits for LineWriter<W>
impl<W: Write> Write for LineWriter<W>

Creates a new LineWriter.

Examples

use std::fs::File;
use std::io::LineWriter;

fn main() -> std::io::Result<()> {
    let file = File::create("poem.txt")?;
    let file = LineWriter::new(file);
    Ok(())
}

pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W>[src]

ⓘImportant traits for LineWriter<W>
impl<W: Write> Write for LineWriter<W>

Creates a new LineWriter with a specified capacity for the internal buffer.

Examples

use std::fs::File;
use std::io::LineWriter;

fn main() -> std::io::Result<()> {
    let file = File::create("poem.txt")?;
    let file = LineWriter::with_capacity(100, file);
    Ok(())
}

pub fn get_ref(&self) -> &W[src]

ⓘImportant traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized, 
    type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'_, R: Read + ?Sized> Read for &'_ mut R
impl<'_, W: Write + ?Sized> Write for &'_ mut W

Gets a reference to the underlying writer.

Examples

use std::fs::File;
use std::io::LineWriter;

fn main() -> std::io::Result<()> {
    let file = File::create("poem.txt")?;
    let file = LineWriter::new(file);

    let reference = file.get_ref();
    Ok(())
}

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

ⓘImportant traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized, 
    type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'_, R: Read + ?Sized> Read for &'_ mut R
impl<'_, W: Write + ?Sized> Write for &'_ mut W

Gets a mutable reference to the underlying writer.

Caution must be taken when calling methods on the mutable reference returned as extra writes could corrupt the output stream.

Examples

use std::fs::File;
use std::io::LineWriter;

fn main() -> std::io::Result<()> {
    let file = File::create("poem.txt")?;
    let mut file = LineWriter::new(file);

    // we can use reference just like file
    let reference = file.get_mut();
    Ok(())
}

pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>>[src]

Unwraps this LineWriter, returning the underlying writer.

The internal 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::fs::File;
use std::io::LineWriter;

fn main() -> std::io::Result<()> {
    let file = File::create("poem.txt")?;

    let writer: LineWriter<File> = LineWriter::new(file);

    let file: File = writer.into_inner()?;
    Ok(())
}

Trait Implementations

impl<W: Write> Write for LineWriter<W>[src]

fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>[src]1.36.0

Like write, except that it writes from a slice of buffers. Read more

fn write_all(&mut self, buf: &[u8]) -> Result<()>[src]

Attempts to write an entire buffer into this writer. Read more

fn write_fmt(&mut self, fmt: Arguments) -> Result<()>[src]

Writes a formatted string into this writer, returning any error encountered. Read more

fn by_ref(&mut self) -> &mut Self where
    Self: Sized
[src]

ⓘImportant traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized, 
    type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'_, R: Read + ?Sized> Read for &'_ mut R
impl<'_, W: Write + ?Sized> Write for &'_ mut W

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

impl<W: Write> Debug for LineWriter<W> where
    W: Debug
[src]

Auto Trait Implementations

impl<W> UnwindSafe for LineWriter<W> where
    W: UnwindSafe

impl<W> RefUnwindSafe for LineWriter<W> where
    W: RefUnwindSafe

impl<W> Unpin for LineWriter<W> where
    W: Unpin

impl<W> Send for LineWriter<W> where
    W: Send

impl<W> Sync for LineWriter<W> where
    W: Sync

Blanket Implementations

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> From<T> for 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]

ⓘImportant traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized, 
    type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'_, R: Read + ?Sized> Read for &'_ mut R
impl<'_, W: Write + ?Sized> Write for &'_ mut W

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

ⓘImportant traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized, 
    type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'_, R: Read + ?Sized> Read for &'_ mut R
impl<'_, W: Write + ?Sized> Write for &'_ mut W

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

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/io/struct.LineWriter.html