std::io::Cursor
Struct std::io::Cursor
pub struct Cursor<T> { /* fields omitted */ }
A Cursor wraps another type and provides it with a Seek implementation.
Cursors are typically used with in-memory buffers 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 more slow 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]);
} Methods
impl<T> Cursor<T>
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fn new(inner: T) -> Cursor<T>
Creates a new cursor wrapping the provided underlying I/O object.
Cursor initial position is 0 even if underlying object (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());
fn into_inner(self) -> T
Consumes this cursor, returning the underlying value.
Examples
use std::io::Cursor; let buff = Cursor::new(Vec::new()); let vec = buff.into_inner();
fn get_ref(&self) -> &T
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();
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
use std::io::Cursor; let mut buff = Cursor::new(Vec::new()); let reference = buff.get_mut();
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);
fn set_position(&mut self, pos: u64)
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);
Trait Implementations
impl<T: Clone> Clone for Cursor<T>
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fn clone(&self) -> Cursor<T>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source. Read more
impl<T: Debug> Debug for Cursor<T>
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fn fmt(&self, __arg_0: &mut Formatter) -> Result
Formats the value using the given formatter.
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>
Seek to an offset, in bytes, in a stream. Read more
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>
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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>
Read all bytes until EOF in this source, placing them into buf. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>1.6.0
Read the exact number of bytes required to fill buf. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Self: Sized,
Creates a "by reference" adaptor for this instance of Read. Read more
fn bytes(self) -> Bytes<Self> where
Self: Sized,
Self: Sized,
Transforms this Read instance to an Iterator over its bytes. Read more
fn chars(self) -> Chars<Self> where
Self: Sized,
Self: Sized,
Transforms this Read instance to an Iterator over chars. Read more
fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
Self: Sized,
Self: Sized,
Creates an adaptor which will chain this stream with another. Read more
fn take(self, limit: u64) -> Take<Self> where
Self: Sized,
Self: Sized,
Creates an adaptor which will read at most limit bytes from it. Read more
impl<T> BufRead for Cursor<T> where
T: AsRef<[u8]>,
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T: AsRef<[u8]>,
fn fill_buf(&mut self) -> Result<&[u8]>
Fills the internal buffer of this object, returning the buffer contents. Read more
fn consume(&mut self, amt: usize)
Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to read. Read more
fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>
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>
Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer. Read more
fn split(self, byte: u8) -> Split<Self> where
Self: Sized,
Self: Sized,
Returns an iterator over the contents of this reader split on the byte byte. Read more
fn lines(self) -> Lines<Self> where
Self: Sized,
Self: Sized,
Returns an iterator over the lines of this reader. Read more
impl<'a> Write for Cursor<&'a mut [u8]>
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fn write(&mut self, data: &[u8]) -> Result<usize>
Write a buffer into this object, returning how many bytes were written. Read more
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this write. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
Writes a formatted string into this writer, returning any error encountered. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
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>
Write a buffer into this object, returning how many bytes were written. Read more
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this write. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
Writes a formatted string into this writer, returning any error encountered. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Self: Sized,
Creates a "by reference" adaptor for this instance of Write. Read more
impl Write for Cursor<Box<[u8]>>
1.5.0
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fn write(&mut self, buf: &[u8]) -> Result<usize>
Write a buffer into this object, returning how many bytes were written. Read more
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this write. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
Writes a formatted string into this writer, returning any error encountered. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Self: Sized,
Creates a "by reference" adaptor for this instance of Write. Read more
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/io/struct.Cursor.html
