Struct `LineWriter`

struct LineWriter<W: ?Sized + Write> { ... }

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(())
}

Implementations

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

fn get_ref(self: &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(())
}

`impl<W: Write> LineWriter<W>`

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(())
}

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(())
}

fn get_mut(self: &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(())
}

fn into_inner(self: 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(())
}

`impl<T> Any for LineWriter<W>`

fn type_id(self: &Self) -> TypeId

`impl<T> Borrow for LineWriter<W>`

fn borrow(self: &Self) -> &T

`impl<T> BorrowMut for LineWriter<W>`

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

`impl<T> From for LineWriter<W>`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T, U> Into for LineWriter<W>`

fn into(self: Self) -> U

Calls U::from(self).

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

`impl<T, U> TryFrom for LineWriter<W>`

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

`impl<T, U> TryInto for LineWriter<W>`

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

`impl<W> Debug for LineWriter<W>`

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

`impl<W> Freeze for LineWriter<W>`

`impl<W> RefUnwindSafe for LineWriter<W>`

`impl<W> Send for LineWriter<W>`

`impl<W> Sync for LineWriter<W>`

`impl<W> Unpin for LineWriter<W>`

`impl<W> UnsafeUnpin for LineWriter<W>`

`impl<W> UnwindSafe for LineWriter<W>`

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

fn write(self: &mut Self, buf: &[u8]) -> Result<usize>
fn flush(self: &mut Self) -> Result<()>
fn write_vectored(self: &mut Self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn is_write_vectored(self: &Self) -> bool
fn write_all(self: &mut Self, buf: &[u8]) -> Result<()>
fn write_all_vectored(self: &mut Self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_fmt(self: &mut Self, fmt: Arguments<'_>) -> Result<()>