1.0.0[][src]Struct std::io::Cursor

pub struct Cursor<T> { /* fields omitted */ }

A Cursor wraps an in-memory buffer and provides it with a Seek implementation.

Cursors are used with in-memory buffers, anything implementing AsRef<[u8]>, to allow them to implement Read and/or Write, allowing these buffers to be used anywhere you might use a reader or writer that does actual I/O.

The standard library implements some I/O traits on various types which are commonly used as a buffer, like Cursor<Vec<u8>> and Cursor<&[u8]>.

Examples

We may want to write bytes to a File in our production code, but use an in-memory buffer in our tests. We can do this with Cursor:

use std::io::prelude::*;
use std::io::{self, SeekFrom};
use std::fs::File;

// a library function we've written
fn write_ten_bytes_at_end<W: Write + Seek>(writer: &mut W) -> io::Result<()> {
    writer.seek(SeekFrom::End(-10))?;

    for i in 0..10 {
        writer.write(&[i])?;
    }

    // all went well
    Ok(())
}

// Here's some code that uses this library function.
//
// We might want to use a BufReader here for efficiency, but let's
// keep this example focused.
let mut file = File::create("foo.txt")?;

write_ten_bytes_at_end(&mut file)?;

// now let's write a test
#[test]
fn test_writes_bytes() {
    // setting up a real File is much slower than an in-memory buffer,
    // let's use a cursor instead
    use std::io::Cursor;
    let mut buff = Cursor::new(vec![0; 15]);

    write_ten_bytes_at_end(&mut buff).unwrap();

    assert_eq!(&buff.get_ref()[5..15], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
}Run

Methods

impl<T> Cursor<T>[src]

Important traits for Cursor<T>
pub fn new(inner: T) -> Cursor<T>[src]

Creates a new cursor wrapping the provided underlying in-memory buffer.

Cursor initial position is 0 even if underlying buffer (e.g., Vec) is not empty. So writing to cursor starts with overwriting Vec content, not with appending to it.

Examples

use std::io::Cursor;

let buff = Cursor::new(Vec::new());Run

pub fn into_inner(self) -> T[src]

Consumes this cursor, returning the underlying value.

Examples

use std::io::Cursor;

let buff = Cursor::new(Vec::new());

let vec = buff.into_inner();Run

Important traits for &'_ mut I
pub fn get_ref(&self) -> &T[src]

Gets a reference to the underlying value in this cursor.

Examples

use std::io::Cursor;

let buff = Cursor::new(Vec::new());

let reference = buff.get_ref();Run

Important traits for &'_ mut I
pub fn get_mut(&mut self) -> &mut T[src]

Gets a mutable reference to the underlying value in this cursor.

Care should be taken to avoid modifying the internal I/O state of the underlying value as it may corrupt this cursor's position.

Examples

use std::io::Cursor;

let mut buff = Cursor::new(Vec::new());

let reference = buff.get_mut();Run

pub fn position(&self) -> u64[src]

Returns the current position of this cursor.

Examples

use std::io::Cursor;
use std::io::prelude::*;
use std::io::SeekFrom;

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.seek(SeekFrom::Current(2)).unwrap();
assert_eq!(buff.position(), 2);

buff.seek(SeekFrom::Current(-1)).unwrap();
assert_eq!(buff.position(), 1);Run

pub fn set_position(&mut self, pos: u64)[src]

Sets the position of this cursor.

Examples

use std::io::Cursor;

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.set_position(2);
assert_eq!(buff.position(), 2);

buff.set_position(4);
assert_eq!(buff.position(), 4);Run

Trait Implementations

impl<T> Read for Cursor<T> where
    T: AsRef<[u8]>, 
[src]

impl<'_> Write for Cursor<&'_ mut [u8]>[src]

impl<'_> Write for Cursor<&'_ mut Vec<u8>>1.25.0[src]

impl Write for Cursor<Vec<u8>>[src]

impl Write for Cursor<Box<[u8]>>1.5.0[src]

impl<T> Seek for Cursor<T> where
    T: AsRef<[u8]>, 
[src]

impl<T> BufRead for Cursor<T> where
    T: AsRef<[u8]>, 
[src]

impl<T: Debug> Debug for Cursor<T>[src]

impl<T: Clone> Clone for Cursor<T>[src]

impl<T: Default> Default for Cursor<T>[src]

Auto Trait Implementations

impl<T> UnwindSafe for Cursor<T> where
    T: UnwindSafe

impl<T> RefUnwindSafe for Cursor<T> where
    T: RefUnwindSafe

impl<T> Unpin for Cursor<T> where
    T: Unpin

impl<T> Send for Cursor<T> where
    T: Send

impl<T> Sync for Cursor<T> where
    T: Sync

Blanket Implementations

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

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

type Error = !

The type returned in the event of a conversion error.

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

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.

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

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

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

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.