Bir dosya bir BufReader ile nasıl kullanılır ve hala buna yazabilir?

Question

Bir dosya açmak ve içeriğini BufReader kullanarak lines() kullanarak okumak istiyorum. Ayrıca dosyanın sonuna kadar arama yapmak ve yeni satırlar yazabilmek istiyorum.

beni dosyaya yazma let mut file sağlar kullanarak, ama BufReader dosyayı verdik bir kere ana işlevi artık sahibi olarak artık, yazabildiğinizi file:

fn main() { 
    let filename = "tt.txt"; 

    // open a tt.txt file in the local directory 
    let file = OpenOptions::new() 
     .read(true) 
     .write(true) 
     .create(true) 
     .open(filename) 
     .unwrap(); 

    // now read the whole file to get the latest state 
    let date_re = Regex::new(r"^(\d{4})-(\d{2})-(\d{2})").unwrap(); 
    let time_activity_re = Regex::new(r"^(\d{2}):(\d{2})\s*(.*)").unwrap(); 
    let reader = BufReader::new(file); 
    let mut latest_date: Option<Date<Local>> = None; 
    let mut latest_datetime: Option<DateTime<Local>> = None; 
    let mut latest_activity: Option<String> = None; 

    for wrapped_line in reader.lines() { 
     let line = wrapped_line.unwrap(); 
     println!("line: {}", line); 

     if date_re.is_match(&line) { 
      let captures = date_re.captures(&line).unwrap(); 
      let year = captures.at(1).unwrap().parse::<i32>().unwrap(); 
      let month = captures.at(2).unwrap().parse::<u32>().unwrap(); 
      let day = captures.at(3).unwrap().parse::<u32>().unwrap(); 
      latest_date = Some(Local.ymd(year, month, day)); 
      latest_datetime = None; 
      latest_activity = None; 
     } 

     if time_activity_re.is_match(&line) && latest_date != None { 
      let captures = time_activity_re.captures(&line).unwrap(); 
      let hour = captures.at(1).unwrap().parse::<u32>().unwrap(); 
      let minute = captures.at(2).unwrap().parse::<u32>().unwrap(); 
      let activity = captures.at(3).unwrap(); 

      latest_datetime = Some(latest_date.unwrap().and_hms(hour, minute, 0)); 

      latest_activity = if activity.len() > 0 { 
       // TODO: if latest_activity already constains a string, clear it and reuse it 
       // as per: https://stackoverflow.com/questions/33781625/how-to-allocate-a-string-before-you-know-how-big-it-needs-to-be 
       Some(activity.to_string()) 
      } else { 
       None 
      }; 

      println!("time activity: {} |{}|", latest_datetime.unwrap(), activity); 
     } 
    } 

    // FIXME: I have to open a second file descriptor to the same file, in order to be able to write to it 
    let mut out = OpenOptions::new() 
     .read(true) 
     .write(true) 
     .create(true) 
     .open(filename) 
     .unwrap(); 

    out.seek(End(0)); 

    let now = Local::now(); 
    if latest_date == None || latest_date.unwrap().year() != now.year() 
     || latest_date.unwrap().month() != now.month() 
     || latest_date.unwrap().day() != now.day() 
    { 
     if (latest_date != None) { 
      // not an empy file, as far as tt is concerned 
      out.write_all(b"\n\n"); 
     } 
     out.write_all(format!("{}\n", now.format("%Y-%m-%d")).as_bytes()); 
     out.write_all(b"\n"); 
    } 

    let activity = env::args().skip(1).join(" "); 
    if (activity.len() > 0) { 
     out.write_all(format!("{} {}\n", now.format("%H:%M"), activity).as_bytes()); 
    } else { 
     // if there was no latest activity *and* there is no activity, then there's no point in writing a second blank line with just a time 
     if latest_activity == None { 
      return; 
     } 
     out.write_all(format!("{}\n", now.format("%H:%M")).as_bytes()); 
    } 

    // FIXME: we're just relying on the program exit to close the two file descriptors (which point at the same file). 
} 

Nasıl Mevcut satırları okumak ve yeni satırları eklemek için tek bir dosya tanıtıcı kullanıyorum? (https://github.com/chrisdew/tt/blob/e899f252014391f2e01c3cc9e281cab1ab88936f/src/main.rs Kod)

Answer 1

bir değeri hareketli önlemek için, bir referans ve yeni bir kapsam kullanabilirsiniz. Bunu BufReader geçirilen geçirildikten sonra dosyayı "kurtarmak" için BufReader::into_inner kullanabilirsiniz

fn main() { 
    let filename = "tt.txt"; 

    // open a tt.txt file in the local directory 
    let mut file = OpenOptions::new() 
     .read(true) 
     .write(true) 
     .create(true) 
     .open(filename) 
     .unwrap(); 

    // now read the whole file to get the latest state 
    let date_re = Regex::new(r"^(\d{4})-(\d{2})-(\d{2})").unwrap(); 
    let time_activity_re = Regex::new(r"^(\d{2}):(\d{2})\s*(.*)").unwrap(); 
    { 
     // BufReader now borrows the value instead of taking ownership. 
     let reader = BufReader::new(&mut file); 
     let mut latest_date: Option<Date<Local>> = None; 
     let mut latest_datetime: Option<DateTime<Local>> = None; 
     let mut latest_activity: Option<String> = None; 

     for wrapped_line in reader.lines() { 
      let line = wrapped_line.unwrap(); 
      println!("line: {}", line); 

      if date_re.is_match(&line) { 
       let captures = date_re.captures(&line).unwrap(); 
       let year = captures.at(1).unwrap().parse::<i32>().unwrap(); 
       let month = captures.at(2).unwrap().parse::<u32>().unwrap(); 
       let day = captures.at(3).unwrap().parse::<u32>().unwrap(); 
       latest_date = Some(Local.ymd(year, month, day)); 
       latest_datetime = None; 
       latest_activity = None; 
      } 

      if time_activity_re.is_match(&line) && latest_date != None { 
       let captures = time_activity_re.captures(&line).unwrap(); 
       let hour = captures.at(1).unwrap().parse::<u32>().unwrap(); 
       let minute = captures.at(2).unwrap().parse::<u32>().unwrap(); 
       let activity = captures.at(3).unwrap(); 

       latest_datetime = Some(latest_date.unwrap().and_hms(hour, minute, 0)); 

       latest_activity = if activity.len() > 0 { 
        // TODO: if latest_activity already constains a string, clear it and reuse it 
        // as per: https://stackoverflow.com/questions/33781625/how-to-allocate-a-string-before-you-know-how-big-it-needs-to-be 
        Some(activity.to_string()) 
       } else { 
        None 
       }; 

       println!("time activity: {} |{}|", latest_datetime.unwrap(), activity); 
      } 
     } 
    } 
    // End of the scope, so now file is not borrowed anymore. 

    file.seek(End(0)); 

    let now = Local::now(); 
    if latest_date == None || latest_date.unwrap().year() != now.year() 
     || latest_date.unwrap().month() != now.month() 
     || latest_date.unwrap().day() != now.day() 
    { 
     if (latest_date != None) { 
      // not an empy file, as far as tt is concerned 
      file.write_all(b"\n\n"); 
     } 
     file.write_all(format!("{}\n", now.format("%Y-%m-%d")).as_bytes()); 
     file.write_all(b"\n"); 
    } 

    let activity = env::args().skip(1).join(" "); 
    if (activity.len() > 0) { 
     file.write_all(format!("{} {}\n", now.format("%H:%M"), activity).as_bytes()); 
    } else { 
     // if there was no latest activity *and* there is no activity, then there's no point in writing a second blank line with just a time 
     if latest_activity == None { 
      return; 
     } 
     file.write_all(format!("{}\n", now.format("%H:%M")).as_bytes()); 
    } 

    // FIXME: we're just relying on the program exit to close the two file descriptors (which point at the same file). 
} 

Answer 2

: Burada Bunu nasıl olduğunu.

use std::fs::File; 
use std::io::{BufRead, BufReader, Write}; 

fn example(mut file: File) { 
    { 
     let reader = BufReader::new(&file); 
     for _ in reader.lines() {} 
    } 

    file.write_all(b"new stuff").unwrap(); 
} 

olmayan sözcük ömürleri: Burada

use std::fs::File; 
use std::io::{BufRead, BufReader, Read, Write}; 

fn example(file: File) { 
    let mut reader = BufReader::new(file); 
    for _ in reader.by_ref().lines() {} 

    let mut out = reader.into_inner(); 

    out.write_all(b"new stuff").unwrap(); 
} 

benzer azaltılmış koduyla antoyo's solution geçerli: Bu ilk etapta BufReader<File> sahipliğini veriyor önlemek için Read::by_ref ile birlikte kullanılabilir (NLL) uygulanır, bu ekstra parantezleri kaldırarak basitleştirilebilir.