I need a completely in-memory object that I can give to BufReader
and BufWriter
. Something like Python's StringIO
. I want to write to and read from such an object using methods ordinarily used with File
s.
Is there a way to do this using the standard library?
In fact there is a way: Cursor<T>
!
(please also read Shepmaster's answer on why often it's even easier)
In the documentation you can see that there are the following impls:
impl<T> Seek for Cursor<T> where T: AsRef<[u8]>
impl<T> Read for Cursor<T> where T: AsRef<[u8]>
impl Write for Cursor<Vec<u8>>
impl<T> AsRef<[T]> for Vec<T>
From this you can see that you can use the type Cursor<Vec<u8>>
just as an ordinary file, because Read
, Write
and Seek
are implemented for that type!
Little example (Playground):
use std::io::{Cursor, Read, Seek, SeekFrom, Write};
// Create fake "file"
let mut c = Cursor::new(Vec::new());
// Write into the "file" and seek to the beginning
c.write_all(&[1, 2, 3, 4, 5]).unwrap();
c.seek(SeekFrom::Start(0)).unwrap();
// Read the "file's" contents into a vector
let mut out = Vec::new();
c.read_to_end(&mut out).unwrap();
println!("{:?}", out);
For a more useful example, check the documentation linked above.