[][src]Struct csv::WriterBuilder

pub struct WriterBuilder { /* fields omitted */ }

Builds a CSV writer with various configuration knobs.

This builder can be used to tweak the field delimiter, record terminator and more. Once a CSV Writer is built, its configuration cannot be changed.

Methods

impl WriterBuilder
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Create a new builder for configuring CSV writing.

To convert a builder into a writer, call one of the methods starting with from_.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new().from_writer(vec![]);
    wtr.write_record(&["a", "b", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,b,c\nx,y,z\n");
    Ok(())
}

Build a CSV writer from this configuration that writes data to the given file path. The file is truncated if it already exists.

If there was a problem opening the file at the given path, then this returns the corresponding error.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new().from_path("foo.csv")?;
    wtr.write_record(&["a", "b", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;
    wtr.flush()?;
    Ok(())
}

Build a CSV writer from this configuration that writes data to wtr.

Note that the CSV writer is buffered automatically, so you should not wrap wtr in a buffered writer like io::BufWriter.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new().from_writer(vec![]);
    wtr.write_record(&["a", "b", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,b,c\nx,y,z\n");
    Ok(())
}

The field delimiter to use when writing CSV.

The default is b','.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .delimiter(b';')
        .from_writer(vec![]);
    wtr.write_record(&["a", "b", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a;b;c\nx;y;z\n");
    Ok(())
}

Whether to write a header row before writing any other row.

When this is enabled and the serialize method is used to write data with something that contains field names (i.e., a struct), then a header row is written containing the field names before any other row is written.

This option has no effect when using other methods to write rows. That is, if you don't use serialize, then you must write your header row explicitly if you want a header row.

This is enabled by default.

Example: with headers

This shows how the header will be automatically written from the field names of a struct.

extern crate csv;
#[macro_use]
extern crate serde_derive;

use std::error::Error;
use csv::WriterBuilder;

#[derive(Serialize)]
struct Row<'a> {
    city: &'a str,
    country: &'a str,
    // Serde allows us to name our headers exactly,
    // even if they don't match our struct field names.
    #[serde(rename = "popcount")]
    population: u64,
}

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new().from_writer(vec![]);
    wtr.serialize(Row {
        city: "Boston",
        country: "United States",
        population: 4628910,
    })?;
    wtr.serialize(Row {
        city: "Concord",
        country: "United States",
        population: 42695,
    })?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "\
city,country,popcount
Boston,United States,4628910
Concord,United States,42695
");
    Ok(())
}

Example: without headers

This shows that serializing things that aren't structs (in this case, a tuple struct) won't result in a header row being written. This means you usually don't need to set has_headers(false) unless you explicitly want to both write custom headers and serialize structs.

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new().from_writer(vec![]);
    wtr.serialize(("Boston", "United States", 4628910))?;
    wtr.serialize(("Concord", "United States", 42695))?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "\
Boston,United States,4628910
Concord,United States,42695
");
    Ok(())
}

Whether the number of fields in records is allowed to change or not.

When disabled (which is the default), writing CSV data will return an error if a record is written with a number of fields different from the number of fields written in a previous record.

When enabled, this error checking is turned off.

Example: writing flexible records

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .flexible(true)
        .from_writer(vec![]);
    wtr.write_record(&["a", "b"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,b\nx,y,z\n");
    Ok(())
}

Example: error when flexible is disabled

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .flexible(false)
        .from_writer(vec![]);
    wtr.write_record(&["a", "b"])?;
    let err = wtr.write_record(&["x", "y", "z"]).unwrap_err();
    match *err.kind() {
        csv::ErrorKind::UnequalLengths { expected_len, len, .. } => {
            assert_eq!(expected_len, 2);
            assert_eq!(len, 3);
        }
        ref wrong => {
            panic!("expected UnequalLengths but got {:?}", wrong);
        }
    }
    Ok(())
}

The record terminator to use when writing CSV.

A record terminator can be any single byte. The default is \n.

Note that RFC 4180 specifies that record terminators should be \r\n. To use \r\n, use the special Terminator::CRLF value.

Example: CRLF

This shows how to use RFC 4180 compliant record terminators.

extern crate csv;

use std::error::Error;
use csv::{Terminator, WriterBuilder};

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .terminator(Terminator::CRLF)
        .from_writer(vec![]);
    wtr.write_record(&["a", "b", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,b,c\r\nx,y,z\r\n");
    Ok(())
}

The quoting style to use when writing CSV.

By default, this is set to QuoteStyle::Necessary, which will only use quotes when they are necessary to preserve the integrity of data.

Note that unless the quote style is set to Never, an empty field is quoted if it is the only field in a record.

Example: non-numeric quoting

This shows how to quote non-numeric fields only.

extern crate csv;

use std::error::Error;
use csv::{QuoteStyle, WriterBuilder};

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .quote_style(QuoteStyle::NonNumeric)
        .from_writer(vec![]);
    wtr.write_record(&["a", "5", "c"])?;
    wtr.write_record(&["3.14", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "\"a\",5,\"c\"\n3.14,\"y\",\"z\"\n");
    Ok(())
}

Example: never quote

This shows how the CSV writer can be made to never write quotes, even if it sacrifices the integrity of the data.

extern crate csv;

use std::error::Error;
use csv::{QuoteStyle, WriterBuilder};

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .quote_style(QuoteStyle::Never)
        .from_writer(vec![]);
    wtr.write_record(&["a", "foo\nbar", "c"])?;
    wtr.write_record(&["g\"h\"i", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,foo\nbar,c\ng\"h\"i,y,z\n");
    Ok(())
}

The quote character to use when writing CSV.

The default is b'"'.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .quote(b'\'')
        .from_writer(vec![]);
    wtr.write_record(&["a", "foo\nbar", "c"])?;
    wtr.write_record(&["g'h'i", "y\"y\"y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,'foo\nbar',c\n'g''h''i',y\"y\"y,z\n");
    Ok(())
}

Enable double quote escapes.

This is enabled by default, but it may be disabled. When disabled, quotes in field data are escaped instead of doubled.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .double_quote(false)
        .from_writer(vec![]);
    wtr.write_record(&["a", "foo\"bar", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,\"foo\\\"bar\",c\nx,y,z\n");
    Ok(())
}

The escape character to use when writing CSV.

In some variants of CSV, quotes are escaped using a special escape character like \ (instead of escaping quotes by doubling them).

By default, writing these idiosyncratic escapes is disabled, and is only used when double_quote is disabled.

Example

extern crate csv;

use std::error::Error;
use csv::WriterBuilder;

fn example() -> Result<(), Box<Error>> {
    let mut wtr = WriterBuilder::new()
        .double_quote(false)
        .escape(b'$')
        .from_writer(vec![]);
    wtr.write_record(&["a", "foo\"bar", "c"])?;
    wtr.write_record(&["x", "y", "z"])?;

    let data = String::from_utf8(wtr.into_inner()?)?;
    assert_eq!(data, "a,\"foo$\"bar\",c\nx,y,z\n");
    Ok(())
}

Set the capacity (in bytes) of the internal buffer used in the CSV writer. This defaults to a reasonable setting.

Trait Implementations

impl Default for WriterBuilder
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impl Debug for WriterBuilder
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Auto Trait Implementations

Blanket Implementations

impl<T> From for T
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impl<T, U> Into for T where
    U: From<T>, 
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impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

impl<T> Borrow for T where
    T: ?Sized
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impl<T> BorrowMut for T where
    T: ?Sized
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impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

impl<T> Any for T where
    T: 'static + ?Sized
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