std::io::LineWriter - Rust
Description: API documentation for the Rust `LineWriter` struct in crate `std`.
Keywords: rust, rustlang, rust-lang, LineWriter

# Struct std::io::LineWriter 1.0.0 [−] [src]

    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.

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::File;
    use std::io::prelude::*;
    use std::io::LineWriter;

    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);

    for &byte in road_not_taken.iter() {
       file.write(&[byte]).unwrap();
    }

    // let's check we did the right thing.
    let mut file = File::open("poem.txt")?;
    let mut contents = String::new();

    file.read_to_string(&mut contents)?;

    assert_eq!(contents.as_bytes(), &road_not_taken[..]);Run

## Methods

### `impl<W: Write> LineWriter<W>`
[src]

#### `fn new(inner: W) -> LineWriter<W>`

Creates a new `LineWriter`.

# Examples

    use std::fs::File;
    use std::io::LineWriter;

    let file = File::create("poem.txt")?;
    let file = LineWriter::new(file);Run

#### `fn with_capacity(cap: usize, inner: W) -> LineWriter<W>`

Creates a new `LineWriter` with a specified capacity for the internal buffer.

# Examples

    use std::fs::File;
    use std::io::LineWriter;

    let file = File::create("poem.txt")?;
    let file = LineWriter::with_capacity(100, file);Run

#### `fn get_ref(&self) -> &W`

Gets a reference to the underlying writer.

# Examples

    use std::fs::File;
    use std::io::LineWriter;

    let file = File::create("poem.txt")?;
    let file = LineWriter::new(file);

    let reference = file.get_ref();Run

#### `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;

    let file = File::create("poem.txt")?;
    let mut file = LineWriter::new(file);

    // we can use reference just like file
    let reference = file.get_mut();Run

#### `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.

# Examples

    use std::fs::File;
    use std::io::LineWriter;

    let file = File::create("poem.txt")?;

    let writer: LineWriter<File> = LineWriter::new(file);

    let file: File = writer.into_inner()?;Run

## Trait Implementations

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

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

Write a buffer into this object, returning how many bytes were written. Read more

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

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

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

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

#### `fn write_fmt(&mut self, fmt: Arguments) -> Result<()>`

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

#### `fn by_ref(&mut self) -> &mut Self where Self: Sized`

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

### `impl<W: Write> Debug for LineWriter<W> where W: Debug`
[src]

#### `fn fmt(&self, fmt: &mut Formatter) -> Result`

Formats the value using the given formatter.

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