Struct Reader 

pub struct Reader<R> { /* private fields */ }

Reads CSV data, either from a byte slice ([from_bytes]) or from any std::io::Read source ([from_reader], requires std feature).

Rows are yielded by calling rows, which returns an iterator of Row<'_>. Errors are deferred to the Row methods.

Example

use csv::Reader;
use std::fs::File;

let mut reader = Reader::from_reader(File::open("data.csv")?);
for row in reader.rows() {
    for field in row.fields()? {
    }
}

Headers

Use parse_headers to read the first row as column headers.

Implementations

impl<R> Reader<R>

pub fn set_delimiter(&mut self, byte: u8) -> &mut Self

Set the field delimiter byte (default is ,).

pub fn set_headers(&mut self, headers: Vec<String>) -> &mut Self

Set column headers manually.

Use this when the CSV file has no header row but you still want Row::deserialize to map struct fields by column name.

Must be called before iterating with rows.

use csv::Reader;
let mut reader = Reader::from_reader(std::io::Cursor::new(b"Alice,30\nBob,25\n"));
reader.set_headers(vec!["name".into(), "age".into()]);
for row in reader.rows() {
    // row.deserialize::<MyStruct>() will match name/age by header
}

pub fn headers(&self) -> Option<&[String]>

Return the column headers, if parse_headers or set_headers was called.

impl<R: Read> Reader<R>

pub fn from_reader(source: R) -> Self

Create a reader from any std::io::Read source.

Data is streamed in chunks as rows are parsed, without loading the entire input into memory.

pub fn parse_headers(&mut self) -> Result<Vec<String>, ReadError>

Read and return the first row as column headers.

If the CSV has no header row, use set_headers instead.

pub fn rows(&mut self) -> Rows<'_, R>

Return an iterator over the remaining rows.

impl<'a> Reader<&'a [u8]>

pub fn from_bytes(bytes: &'a [u8]) -> Self

Create a reader from a byte slice for in-memory parsing.

Unlike [from_reader], this does not require std and copies the input into an internal buffer eagerly.

use csv::Reader;
let mut reader = Reader::from_bytes(b"a,b\n1,2\n");
let fields: Vec<Vec<String>> = reader.rows().map(|r| r.all().unwrap()).collect();
assert_eq!(fields, vec![vec!["a".to_string(), "b".to_string()], vec!["1".to_string(), "2".to_string()]]);