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(())
}
RunImplementations§
source§impl<W: Write> LineWriter<W>
impl<W: Write> LineWriter<W>
sourcepub fn new(inner: W) -> LineWriter<W> ⓘ
pub fn new(inner: W) -> LineWriter<W> ⓘ
sourcepub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> ⓘ
pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> ⓘ
sourcepub fn get_mut(&mut self) -> &mut W
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(())
}
Runsourcepub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>>
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(())
}
Runsource§impl<W: ?Sized + Write> LineWriter<W>
impl<W: ?Sized + Write> LineWriter<W>
Trait Implementations§
source§impl<W> Debug for LineWriter<W>
impl<W> Debug for LineWriter<W>
source§impl<W: ?Sized + Write> Write for LineWriter<W>
impl<W: ?Sized + Write> Write for LineWriter<W>
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
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