1.0.0[−][src]Struct std::io::Cursor
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]); }Run
Methods
impl<T> Cursor<T>
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ⓘImportant traits for Cursor<T>pub fn new(inner: T) -> Cursor<T>
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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
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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 Fpub fn get_ref(&self) -> &T
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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 Fpub fn get_mut(&mut self) -> &mut T
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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
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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)
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Trait Implementations
impl<T> Read for Cursor<T> where
T: AsRef<[u8]>,
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T: AsRef<[u8]>,
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
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fn read_vectored(&mut self, bufs: &mut [IoSliceMut]) -> Result<usize>
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fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
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unsafe fn initializer(&self) -> Initializer
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fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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Read all bytes until EOF in this source, placing them into buf
. Read more
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
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Read all bytes until EOF in this source, appending them to buf
. Read more
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
Creates a "by reference" adaptor for this instance of Read
. Read more
ⓘImportant traits for Bytes<R>fn bytes(self) -> Bytes<Self> where
Self: Sized,
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Self: Sized,
Transforms this Read
instance to an [Iterator
] over its bytes. Read more
ⓘImportant traits for Chain<T, U>fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
Self: Sized,
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Self: Sized,
Creates an adaptor which will chain this stream with another. Read more
ⓘImportant traits for Take<T>fn take(self, limit: u64) -> Take<Self> where
Self: Sized,
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Self: Sized,
Creates an adaptor which will read at most limit
bytes from it. Read more
impl<'_> Write for Cursor<&'_ mut [u8]>
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fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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Attempts to write an entire buffer into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
Creates a "by reference" adaptor for this instance of Write
. Read more
impl<'_> Write for Cursor<&'_ mut Vec<u8>>
1.25.0[src]
fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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Attempts to write an entire buffer into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
Creates a "by reference" adaptor for this instance of Write
. Read more
impl Write for Cursor<Vec<u8>>
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fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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Attempts to write an entire buffer into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
[src]
Self: Sized,
Creates a "by reference" adaptor for this instance of Write
. Read more
impl Write for Cursor<Box<[u8]>>
1.5.0[src]
fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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Attempts to write an entire buffer into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
Creates a "by reference" adaptor for this instance of Write
. Read more
impl<T> Seek for Cursor<T> where
T: AsRef<[u8]>,
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T: AsRef<[u8]>,
fn seek(&mut self, style: SeekFrom) -> Result<u64>
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fn stream_len(&mut self) -> Result<u64>
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fn stream_position(&mut self) -> Result<u64>
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impl<T> BufRead for Cursor<T> where
T: AsRef<[u8]>,
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T: AsRef<[u8]>,
fn fill_buf(&mut self) -> Result<&[u8]>
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fn consume(&mut self, amt: usize)
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fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>
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Read all bytes into buf
until the delimiter byte
or EOF is reached. Read more
fn read_line(&mut self, buf: &mut String) -> Result<usize>
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Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer. Read more
ⓘImportant traits for Split<B>fn split(self, byte: u8) -> Split<Self> where
Self: Sized,
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Self: Sized,
Returns an iterator over the contents of this reader split on the byte byte
. Read more
ⓘImportant traits for Lines<B>fn lines(self) -> Lines<Self> where
Self: Sized,
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Self: Sized,
Returns an iterator over the lines of this reader. Read more
impl<T: Debug> Debug for Cursor<T>
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impl<T: Clone> Clone for Cursor<T>
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ⓘImportant traits for Cursor<T>fn clone(&self) -> Cursor<T>
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fn clone_from(&mut self, source: &Self)
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Performs copy-assignment from source
. Read more
impl<T: Default> Default for Cursor<T>
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Auto Trait Implementations
Blanket Implementations
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T> From<T> for T
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
ⓘImportant traits for &'_ mut Ffn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> ToOwned for T where
T: Clone,
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T: Clone,