1.0.0[][src]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(())
}Run

Methods

impl<W: Write> LineWriter<W>
[src]

Important traits 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(())
}Run

Important traits 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(())
}Run

Important traits for &'_ mut I

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

Important traits for &'_ mut I

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

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

Trait Implementations

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

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

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

Important traits for &'_ mut I

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

impl<W: Write> Debug for LineWriter<W> where
    W: Debug
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Auto Trait Implementations

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

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

impl<T> From for T
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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.

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

impl<T> Borrow for T where
    T: ?Sized
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impl<T> BorrowMut for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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