csv - 如何附加到现有的 CSV 文件？

Question

例如，当运行下面的代码时，每次以前的 test.csv 文件都会被新文件覆盖。如何附加到 test.csv 而不是覆盖它？

extern crate csv;

use std::error::Error;
use std::process;

fn run() -> Result<(), Box<Error>> {
    let file_path = std::path::Path::new("test.csv");
    let mut wtr = csv::Writer::from_path(file_path).unwrap();

    wtr.write_record(&["City", "State", "Population", "Latitude", "Longitude"])?;
    wtr.write_record(&["Davidsons Landing", "AK", "", "65.2419444", "-165.2716667"])?;
    wtr.write_record(&["Kenai", "AK", "7610", "60.5544444", "-151.2583333"])?;
    wtr.write_record(&["Oakman", "AL", "", "33.7133333", "-87.3886111"])?;

    wtr.flush()?;
    Ok(())
}

fn main() {
    if let Err(err) = run() {
        println!("{}", err);
        process::exit(1);
    }
}

如果文件尚不存在，追加解决方案是否有效？

Answer 1

csv crate 提供 Writer::from_writer所以你可以使用任何实现 Write 的东西.使用 File 时, this answer来自 What is the best variant for appending a new line in a text file?显示解决方案:

Using OpenOptions::append is the clearest way to append to a file

let mut file = OpenOptions::new()
    .write(true)
    .append(true)
    .open("test.csv")
    .unwrap();
let mut wtr = csv::Writer::from_writer(file);

Will the append solution work if the file does not yet exist?

只需将 create(true) 添加到 OpenOptions 即可:

let mut file = OpenOptions::new()
    .write(true)
    .create(true)
    .append(true)
    .open("test.csv")
    .unwrap();
let mut wtr = csv::Writer::from_writer(file);