# 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

## Implementations

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

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

### Notable traits for LineWriter<W>

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

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

#### `pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W>ⓘ

### Notable traits for LineWriter<W>

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

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

#### `pub fn get_ref(&self) -> &Wⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

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

#### `pub fn get_mut(&mut self) -> &mut Wⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

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

#### `pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>>`[src]

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> Debug for LineWriter<W> where
W: Debug,` [src]

#### `pub fn fmt(&self, fmt: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

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

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

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

#### `pub fn flush(&mut self) -> Result<()>`[src]

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

#### `pub fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>`[src]

Like `write`, except that it writes from a slice of buffers. Read more

#### `pub fn is_write_vectored(&self) -> bool`[src]

🔬 This is a nightly-only experimental API. (`can_vector` #69941)

Determines if this `Write`r has an efficient `write_vectored` implementation. Read more

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

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

#### `pub fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>`[src]

🔬 This is a nightly-only experimental API. (`write_all_vectored` #70436)

Attempts to write multiple buffers into this writer. Read more

#### `pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>`[src]

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

#### `pub fn by_ref(&mut self) -> &mut Selfⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W`
where
Self: Sized,` [src]

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

## Auto Trait Implementations

### `impl<W> RefUnwindSafe for LineWriter<W> where
W: RefUnwindSafe,` [src]

### `impl<W> Send for LineWriter<W> where
W: Send,` [src]

### `impl<W> Sync for LineWriter<W> where
W: Sync,` [src]

### `impl<W> Unpin for LineWriter<W> where
W: Unpin,` [src]

### `impl<W> UnwindSafe for LineWriter<W> where
W: UnwindSafe,` [src]

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&self) -> &Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut self) -> &mut Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T`[src]

#### `pub fn from(t: T) -> T`[src]

Performs the conversion.

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

#### `pub fn into(self) -> U`[src]

Performs the conversion.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.