How to append to an existing CSV file? - csv

Question

As an example, when the below code is run, each time the previous test.csv file is overwritten with a new one. How to append to test.csv instead of overwriting it?
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);
}
}
Will the append solution work if the file does not yet exist?

Answer 1

The csv crate provides Writer::from_writer so you can use anything, which implements Write. When using File, this answer from What is the best variant for appending a new line in a text file? shows a solution:
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?
Just add create(true) to the OpenOptions:
let mut file = OpenOptions::new()
.write(true)
.create(true)
.append(true)
.open("test.csv")
.unwrap();
let mut wtr = csv::Writer::from_writer(file);