1.0.0[−][src]Struct std::io::Cursor  
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] 
impl<T> Cursor<T>ⓘImportant traits for Cursor<T>pub fn new(inner: T) -> Cursor<T>[src] 
pub fn new(inner: T) -> Cursor<T>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] 
pub fn into_inner(self) -> TConsumes 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 &'a mut Ipub fn get_ref(&self) -> &T[src] 
pub fn get_ref(&self) -> &TGets 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 &'a mut Ipub fn get_mut(&mut self) -> &mut T[src] 
pub fn get_mut(&mut self) -> &mut TGets 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] 
pub fn position(&self) -> u64Returns 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] 
pub fn set_position(&mut self, pos: u64)Trait Implementations
impl<T: Clone> Clone for Cursor<T>[src] 
impl<T: Clone> Clone for Cursor<T>ⓘImportant traits for Cursor<T>fn clone(&self) -> Cursor<T>[src] 
fn clone(&self) -> Cursor<T>Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)[src] 
fn clone_from(&mut self, source: &Self)Performs copy-assignment from source. Read more
impl<T: Debug> Debug for Cursor<T>[src] 
impl<T: Debug> Debug for Cursor<T>fn fmt(&self, f: &mut Formatter) -> Result[src] 
fn fmt(&self, f: &mut Formatter) -> ResultFormats the value using the given formatter. Read more
impl<T> Seek for Cursor<T> where
    T: AsRef<[u8]>, [src] 
impl<T> Seek for Cursor<T> where
    T: AsRef<[u8]>, fn seek(&mut self, style: SeekFrom) -> Result<u64>[src] 
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]>, [src] 
impl<T> Read for Cursor<T> where
    T: AsRef<[u8]>, fn read(&mut self, buf: &mut [u8]) -> Result<usize>[src] 
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_exact(&mut self, buf: &mut [u8]) -> Result<()>[src] 
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>Read the exact number of bytes required to fill buf. Read more
unsafe fn initializer(&self) -> Initializer[src] 
unsafe fn initializer(&self) -> InitializerDetermines if this Reader can work with buffers of uninitialized memory. Read more
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>[src] 
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>[src] 
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>Read all bytes until EOF in this source, appending them to buf. Read more
ⓘImportant traits for &'a mut Ifn by_ref(&mut self) -> &mut Self where
    Self: Sized, [src] 
fn by_ref(&mut self) -> &mut Self where
    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, [src] 
fn bytes(self) -> Bytes<Self> where
    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, [src] 
fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
    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, [src] 
fn take(self, limit: u64) -> Take<Self> where
    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]>, [src] 
impl<T> BufRead for Cursor<T> where
    T: AsRef<[u8]>, fn fill_buf(&mut self) -> Result<&[u8]>[src] 
fn fill_buf(&mut self) -> Result<&[u8]>Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty. Read more
fn consume(&mut self, amt: usize)[src] 
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>[src] 
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>[src] 
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
ⓘImportant traits for Split<B>fn split(self, byte: u8) -> Split<Self> where
    Self: Sized, [src] 
fn split(self, byte: u8) -> Split<Self> where
    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, [src] 
fn lines(self) -> Lines<Self> where
    Self: Sized, Returns an iterator over the lines of this reader. Read more
impl<'a> Write for Cursor<&'a mut [u8]>[src] 
impl<'a> Write for Cursor<&'a mut [u8]>fn write(&mut self, buf: &[u8]) -> Result<usize>[src] 
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<()>[src] 
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<()>[src] 
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<()>[src] 
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'a mut Ifn by_ref(&mut self) -> &mut Self where
    Self: Sized, [src] 
fn by_ref(&mut self) -> &mut Self where
    Self: Sized, Creates a "by reference" adaptor for this instance of Write. Read more
impl<'a> Write for Cursor<&'a mut Vec<u8>>1.25.0[src] 
impl<'a> Write for Cursor<&'a mut Vec<u8>>fn write(&mut self, buf: &[u8]) -> Result<usize>[src] 
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<()>[src] 
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<()>[src] 
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<()>[src] 
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'a mut Ifn by_ref(&mut self) -> &mut Self where
    Self: Sized, [src] 
fn by_ref(&mut self) -> &mut Self where
    Self: Sized, Creates a "by reference" adaptor for this instance of Write. Read more
impl Write for Cursor<Vec<u8>>[src] 
impl Write for Cursor<Vec<u8>>fn write(&mut self, buf: &[u8]) -> Result<usize>[src] 
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<()>[src] 
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<()>[src] 
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<()>[src] 
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'a mut Ifn by_ref(&mut self) -> &mut Self where
    Self: Sized, [src] 
fn by_ref(&mut self) -> &mut Self where
    Self: Sized, Creates a "by reference" adaptor for this instance of Write. Read more
impl Write for Cursor<Box<[u8]>>1.5.0[src] 
impl Write for Cursor<Box<[u8]>>fn write(&mut self, buf: &[u8]) -> Result<usize>[src] 
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<()>[src] 
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<()>[src] 
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<()>[src] 
fn write_fmt(&mut self, fmt: Arguments) -> Result<()>Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'a mut Ifn by_ref(&mut self) -> &mut Self where
    Self: Sized, [src] 
fn by_ref(&mut self) -> &mut Self where
    Self: Sized, Creates a "by reference" adaptor for this instance of Write. Read more
Auto Trait Implementations
Blanket Implementations
impl<T> From for T[src] 
impl<T> From for Timpl<T, U> TryFrom for T where
    T: From<U>, [src] 
impl<T, U> TryFrom for T where
    T: From<U>, type Error = !
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>[src] 
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>Performs the conversion.
impl<T, U> TryInto for T where
    U: TryFrom<T>, [src] 
impl<T, U> TryInto for T where
    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>[src] 
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>Performs the conversion.
impl<T, U> Into for T where
    U: From<T>, [src] 
impl<T, U> Into for T where
    U: From<T>, impl<T> Borrow for T where
    T: ?Sized, [src] 
impl<T> Borrow for T where
    T: ?Sized, ⓘImportant traits for &'a mut Ifn borrow(&self) -> &T[src] 
fn borrow(&self) -> &TImmutably borrows from an owned value. Read more
impl<T> BorrowMut for T where
    T: ?Sized, [src] 
impl<T> BorrowMut for T where
    T: ?Sized, ⓘImportant traits for &'a mut Ifn borrow_mut(&mut self) -> &mut T[src] 
fn borrow_mut(&mut self) -> &mut TMutably borrows from an owned value. Read more
impl<T> Any for T where
    T: 'static + ?Sized, [src] 
impl<T> Any for T where
    T: 'static + ?Sized, fn get_type_id(&self) -> TypeId[src] 
fn get_type_id(&self) -> TypeId🔬 This is a nightly-only experimental API.  (get_type_id #27745)
this method will likely be replaced by an associated static
Gets the TypeId of self. Read more
impl<T> ToOwned for T where
    T: Clone, [src] 
impl<T> ToOwned for T where
    T: Clone, type Owned = T
fn to_owned(&self) -> T[src] 
fn to_owned(&self) -> TCreates owned data from borrowed data, usually by cloning. Read more
fn clone_into(&self, target: &mut T)[src] 
fn clone_into(&self, target: &mut T)🔬 This is a nightly-only experimental API.  (toowned_clone_into #41263)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more