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>(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]);
}
RunImplementations
sourceimpl<T> Cursor<T>
impl<T> Cursor<T>
const: unstable · sourcepub fn new(inner: T) -> Cursor<T>ⓘNotable traits for Cursor<T>impl<T> Read for Cursor<T>where
T: AsRef<[u8]>,impl Write for Cursor<&mut [u8]>impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,impl<const N: usize> Write for Cursor<[u8; N]>
pub fn new(inner: T) -> Cursor<T>ⓘNotable traits for Cursor<T>impl<T> Read for Cursor<T>where
T: AsRef<[u8]>,impl Write for Cursor<&mut [u8]>impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,impl<const N: usize> Write for Cursor<[u8; N]>
T: AsRef<[u8]>,impl Write for Cursor<&mut [u8]>impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,impl<const N: usize> Write for Cursor<[u8; N]>
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());
Runsourcepub fn into_inner(self) -> T
pub fn into_inner(self) -> T
const: unstable · sourcepub fn position(&self) -> u64
pub fn position(&self) -> u64
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);
Runsourcepub fn set_position(&mut self, pos: u64)
pub fn set_position(&mut self, pos: u64)
sourceimpl<T> Cursor<T>where
T: AsRef<[u8]>,
impl<T> Cursor<T>where
T: AsRef<[u8]>,
sourcepub fn remaining_slice(&self) -> &[u8]ⓘNotable traits for &[u8]impl Read for &[u8]impl Write for &mut [u8]
🔬This is a nightly-only experimental API. (cursor_remaining
#86369)
pub fn remaining_slice(&self) -> &[u8]ⓘNotable traits for &[u8]impl Read for &[u8]impl Write for &mut [u8]
cursor_remaining
#86369)Returns the remaining slice.
Examples
#![feature(cursor_remaining)]
use std::io::Cursor;
let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
assert_eq!(buff.remaining_slice(), &[1, 2, 3, 4, 5]);
buff.set_position(2);
assert_eq!(buff.remaining_slice(), &[3, 4, 5]);
buff.set_position(4);
assert_eq!(buff.remaining_slice(), &[5]);
buff.set_position(6);
assert_eq!(buff.remaining_slice(), &[]);
Runsourcepub fn is_empty(&self) -> bool
🔬This is a nightly-only experimental API. (cursor_remaining
#86369)
pub fn is_empty(&self) -> bool
cursor_remaining
#86369)Returns true
if the remaining slice is empty.
Examples
#![feature(cursor_remaining)]
use std::io::Cursor;
let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
buff.set_position(2);
assert!(!buff.is_empty());
buff.set_position(5);
assert!(buff.is_empty());
buff.set_position(10);
assert!(buff.is_empty());
RunTrait Implementations
sourceimpl<T> BufRead for Cursor<T>where
T: AsRef<[u8]>,
impl<T> BufRead for Cursor<T>where
T: AsRef<[u8]>,
sourcefn fill_buf(&mut self) -> Result<&[u8]>
fn fill_buf(&mut self) -> Result<&[u8]>
sourcefn 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 moresourcefn 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 moresourcefn 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 buffer. You do not need to clear the buffer before
appending. Read moresourceimpl<T: Default> Default for Cursor<T>
impl<T: Default> Default for Cursor<T>
sourcefn default() -> Cursor<T>ⓘNotable traits for Cursor<T>impl<T> Read for Cursor<T>where
T: AsRef<[u8]>,impl Write for Cursor<&mut [u8]>impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,impl<const N: usize> Write for Cursor<[u8; N]>
fn default() -> Cursor<T>ⓘNotable traits for Cursor<T>impl<T> Read for Cursor<T>where
T: AsRef<[u8]>,impl Write for Cursor<&mut [u8]>impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,impl<const N: usize> Write for Cursor<[u8; N]>
T: AsRef<[u8]>,impl Write for Cursor<&mut [u8]>impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,impl<const N: usize> Write for Cursor<[u8; N]>
sourceimpl<T: PartialEq> PartialEq<Cursor<T>> for Cursor<T>
impl<T: PartialEq> PartialEq<Cursor<T>> for Cursor<T>
sourceimpl<T> Read for Cursor<T>where
T: AsRef<[u8]>,
impl<T> Read for Cursor<T>where
T: AsRef<[u8]>,
sourcefn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
sourcefn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)sourcefn 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 moresourcefn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
can_vector
#69941)sourcefn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read moresourcefn 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 moresourcefn read_to_string(&mut self, buf: &mut String) -> Result<usize>
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read moresourcefn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)cursor
. Read moresourcefn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Read
. Read moresourcefn bytes(self) -> Bytes<Self>ⓘNotable traits for Bytes<R>impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
where
Self: Sized,
fn bytes(self) -> Bytes<Self>ⓘNotable traits for Bytes<R>impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
where
Self: Sized,
sourceimpl<T> Seek for Cursor<T>where
T: AsRef<[u8]>,
impl<T> Seek for Cursor<T>where
T: AsRef<[u8]>,
sourcefn seek(&mut self, style: SeekFrom) -> Result<u64>
fn seek(&mut self, style: SeekFrom) -> Result<u64>
sourcefn stream_len(&mut self) -> Result<u64>
fn stream_len(&mut self) -> Result<u64>
seek_stream_len
#59359)sourcefn stream_position(&mut self) -> Result<u64>
fn stream_position(&mut self) -> Result<u64>
sourceimpl Write for Cursor<&mut [u8]>
impl Write for Cursor<&mut [u8]>
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
sourcefn 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 · sourceimpl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,
impl<A> Write for Cursor<&mut Vec<u8, A>>where
A: Allocator,
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
sourcefn 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 · sourceimpl<const N: usize> Write for Cursor<[u8; N]>
impl<const N: usize> Write for Cursor<[u8; N]>
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
sourcefn 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 · sourceimpl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,
impl<A> Write for Cursor<Box<[u8], A>>where
A: Allocator,
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
sourcefn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)sourceimpl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,
impl<A> Write for Cursor<Vec<u8, A>>where
A: Allocator,
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
sourcefn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)