# Function std::io::copy

1.0.0 · source ·

    pub fn copy<R, W>(reader: &mut R, writer: &mut W) -> Result<u64>where
        R: Read + ?Sized,
        W: Write + ?Sized,

Expand description

Copies the entire contents of a reader into a writer.

This function will continuously read data from `reader` and then write it into `writer` in a streaming fashion until `reader` returns EOF.

On success, the total number of bytes that were copied from `reader` to `writer` is returned.

If you want to copy the contents of one file to another and you’re working with filesystem paths, see the `fs::copy` function.

## Errors

This function will return an error immediately if any call to `read` or `write` returns an error. All instances of `ErrorKind::Interrupted` are handled by this function and the underlying operation is retried.

## Examples

    use std::io;

    fn main() -> io::Result<()> {
        let mut reader: &[u8] = b"hello";
        let mut writer: Vec<u8> = vec![];

        io::copy(&mut reader, &mut writer)?;

        assert_eq!(&b"hello"[..], &writer[..]);
        Ok(())
    }

Run

## Platform-specific behavior

On Linux (including Android), this function uses `copy_file_range(2)`, `sendfile(2)` or `splice(2)` syscalls to move data directly between file descriptors if possible.

Note that platform-specific behavior may change in the future.