LineWriter in std::io - Rust (original) (raw)
Struct 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 theLineWriter 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(())
}1.0.0 · Source
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(())
}1.0.0 · Source
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(())
}1.0.0 · Source
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(())
}1.0.0 · Source
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(())
}1.0.0 · Source
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(())
}Writes a buffer into this writer, returning how many bytes were written. Read more
Flushes this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
Like write, except that it writes from a slice of buffers. Read more
🔬This is a nightly-only experimental API. (can_vector #69941)
Attempts to write an entire buffer into this writer. Read more
🔬This is a nightly-only experimental API. (write_all_vectored #70436)
Attempts to write multiple buffers into this writer. Read more
Writes a formatted string into this writer, returning any error encountered. Read more
Creates a “by reference” adapter for this instance of Write. Read more