Struct std::io::LineWriter

1.0.0 · source ·
pub struct LineWriter<W: ?Sized + Write> { /* private fields */ }
Expand description

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(())
}
Run

Implementations§

source§

impl<W: Write> LineWriter<W>

source

pub fn new(inner: W) -> 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(())
}
Run
source

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

Creates a new LineWriter with at least the 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(())
}
Run
source

pub fn get_mut(&mut self) -> &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(())
}
Run
source

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

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(())
}
Run
source§

impl<W: ?Sized + Write> LineWriter<W>

source

pub fn get_ref(&self) -> &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(())
}
Run

Trait Implementations§

source§

impl<W> Debug for LineWriter<W>where W: Debug + ?Sized + Write,

source§

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

impl<W: ?Sized + Write> Write for LineWriter<W>

source§

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

Write a buffer into this writer, returning how many bytes were written. Read more
source§

fn flush(&mut self) -> Result<()>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
source§

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

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

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector #69941)
Determines if this Writer has an efficient write_vectored implementation. Read more
source§

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

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

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>

🔬This is a nightly-only experimental API. (write_all_vectored #70436)
Attempts to write multiple buffers into this writer. Read more
source§

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>

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

Auto Trait Implementations§

§

impl<W: ?Sized> RefUnwindSafe for LineWriter<W>where W: RefUnwindSafe,

§

impl<W: ?Sized> Send for LineWriter<W>where W: Send,

§

impl<W: ?Sized> Sync for LineWriter<W>where W: Sync,

§

impl<W: ?Sized> Unpin for LineWriter<W>where W: Unpin,

§

impl<W: ?Sized> UnwindSafe for LineWriter<W>where W: UnwindSafe,

Blanket Implementations§

source§

impl<T> Any for Twhere T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T> Borrow<T> for Twhere T: ?Sized,

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for Twhere T: ?Sized,

source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T, U> Into<U> for Twhere U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

source§

impl<T, U> TryFrom<U> for Twhere U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

§

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

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.