pub struct Cursor<T> { /* private fields */ }
Expand description
A Cursor
wraps an in-memory buffer and provides it with a
Seek
implementation.
Cursor
s 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>(mut writer: 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")?;
// First, we need to allocate 10 bytes to be able to write into.
file.set_len(10)?;
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]);
}
Implementations§
source§impl<T> Cursor<T>
impl<T> Cursor<T>
1.0.0 (const: 1.79.0) · sourcepub const fn new(inner: T) -> Cursor<T> ⓘ
pub const fn new(inner: T) -> Cursor<T> ⓘ
1.0.0 · sourcepub fn into_inner(self) -> T
pub fn into_inner(self) -> T
Consumes this cursor, returning the underlying value.
§Examples
1.0.0 (const: 1.79.0) · sourcepub const fn get_ref(&self) -> &T
pub const fn get_ref(&self) -> &T
Gets a reference to the underlying value in this cursor.
§Examples
1.0.0 · sourcepub fn get_mut(&mut self) -> &mut T
pub fn get_mut(&mut self) -> &mut T
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
1.0.0 (const: 1.79.0) · sourcepub const fn position(&self) -> u64
pub const fn position(&self) -> u64
Returns the current position of this cursor.
§Examples
1.0.0 · sourcepub fn set_position(&mut self, pos: u64)
pub fn set_position(&mut self, pos: u64)
Sets the position of this cursor.
§Examples
source§impl<T> Cursor<T>
impl<T> Cursor<T>
sourcepub fn split(&self) -> (&[u8], &[u8])
🔬This is a nightly-only experimental API. (cursor_split
#86369)
pub fn split(&self) -> (&[u8], &[u8])
cursor_split
#86369)Splits the underlying slice at the cursor position and returns them.
§Examples
#![feature(cursor_split)]
use std::io::Cursor;
let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
assert_eq!(buff.split(), ([].as_slice(), [1, 2, 3, 4, 5].as_slice()));
buff.set_position(2);
assert_eq!(buff.split(), ([1, 2].as_slice(), [3, 4, 5].as_slice()));
buff.set_position(6);
assert_eq!(buff.split(), ([1, 2, 3, 4, 5].as_slice(), [].as_slice()));
source§impl<T> Cursor<T>
impl<T> Cursor<T>
sourcepub fn split_mut(&mut self) -> (&mut [u8], &mut [u8])
🔬This is a nightly-only experimental API. (cursor_split
#86369)
pub fn split_mut(&mut self) -> (&mut [u8], &mut [u8])
cursor_split
#86369)Splits the underlying slice at the cursor position and returns them mutably.
§Examples
#![feature(cursor_split)]
use std::io::Cursor;
let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
assert_eq!(buff.split_mut(), ([].as_mut_slice(), [1, 2, 3, 4, 5].as_mut_slice()));
buff.set_position(2);
assert_eq!(buff.split_mut(), ([1, 2].as_mut_slice(), [3, 4, 5].as_mut_slice()));
buff.set_position(6);
assert_eq!(buff.split_mut(), ([1, 2, 3, 4, 5].as_mut_slice(), [].as_mut_slice()));
Trait Implementations§
1.0.0 · source§impl<T> BufRead for Cursor<T>
impl<T> BufRead for Cursor<T>
source§fn fill_buf(&mut self) -> Result<&[u8]>
fn fill_buf(&mut self) -> Result<&[u8]>
source§fn consume(&mut self, amt: usize)
fn consume(&mut self, amt: usize)
amt
bytes have been consumed from the buffer,
so they should no longer be returned in calls to read
. Read moresource§fn has_data_left(&mut self) -> Result<bool>
fn has_data_left(&mut self) -> Result<bool>
buf_read_has_data_left
#86423)Read
has any data left to be read. Read more1.84.0 · source§fn skip_until(&mut self, byte: u8) -> Result<usize>
fn skip_until(&mut self, byte: u8) -> Result<usize>
byte
or EOF is reached. Read more1.0.0 · source§fn read_line(&mut self, buf: &mut String) -> Result<usize>
fn read_line(&mut self, buf: &mut String) -> Result<usize>
0xA
byte) is reached, and append
them to the provided String
buffer. Read more1.0.0 · source§impl<T> Read for Cursor<T>
impl<T> Read for Cursor<T>
source§fn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
source§fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)source§fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
read
, except that it reads into a slice of buffers. Read moresource§fn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
can_vector
#69941)source§fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read moresource§fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)cursor
. Read moresource§fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
buf
. Read moresource§fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read more1.0.0 · source§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Read
. Read more1.0.0 · source§impl<T> Seek for Cursor<T>
impl<T> Seek for Cursor<T>
source§fn seek(&mut self, style: SeekFrom) -> Result<u64>
fn seek(&mut self, style: SeekFrom) -> Result<u64>
source§fn stream_len(&mut self) -> Result<u64>
fn stream_len(&mut self) -> Result<u64>
seek_stream_len
#59359)1.0.0 · source§impl Write for Cursor<&mut [u8]>
impl Write for Cursor<&mut [u8]>
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
1.0.0 · source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)1.25.0 · source§impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,
impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
1.0.0 · source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)1.61.0 · source§impl<const N: usize> Write for Cursor<[u8; N]>
impl<const N: usize> Write for Cursor<[u8; N]>
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
1.0.0 · source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)1.5.0 · source§impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,
impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
1.0.0 · source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)1.0.0 · source§impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,
impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
1.0.0 · source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)