Desidero aprire un file e leggerne il contenuto come BufReader
utilizzando lines()
. Voglio anche essere in grado di cercare fino alla fine del file e scrivere alcune nuove righe.Come utilizzare un file con un BufReader ed essere ancora in grado di scrivere su di esso?
Utilizzando let mut file
permette di me scrivere sul file, ma una volta ho dato il file nella BufReader
non riesco più a scrivere su di esso, come la funzione principale non possiede più 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).
}
Come può Uso un singolo descrittore di file per leggere le righe esistenti e aggiungere nuove righe?
(Codice da https://github.com/chrisdew/tt/blob/e899f252014391f2e01c3cc9e281cab1ab88936f/src/main.rs)