How to `read_until` with maximum read limit

help
1

Hi

I'd like to read a file with separator '>' with maximum read limit.

fn main() {
  let mut f = BufReader::new(File::open("Bigfile.txt").unwrap());
  let mut v = Vec::new();

  for _i in 0..100 {
    let tf = f.take(2000);
    tf.read_until(b'>', &mut v).unwrap();
  
    f = tf.into_inner();
  }
  
}

Is this okay?
I'm not sure but I think that take() and into_inner() take some time.

3

BufReader::take is actually Read::take, which literally only creates the struct. Likewise, Take::into_inner moves the field out of struct. The only overhead could be in the implementation of BufRead for Take, but it mostly delegates the work to the inner reader and so should be not worse than anything you could do yourself.

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4

"Thinking" is a spectacularly bad way to understand performance, btw. The only valid way is to measure.

2 Likes
5

You can avoid the into_inner dance if you do f.by_ref().take(2000) (or equivalently (&mut f).take(2000)).

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6

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