Struct csv::WriterBuilder
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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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pub fn new() -> 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(()) }
pub fn from_path<P: AsRef<Path>>(&self, path: P) -> Result<Writer<File>>
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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(()) }
pub fn from_writer<W: Write>(&self, wtr: W) -> Writer<W>
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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(()) }
pub fn delimiter(&mut self, delimiter: u8) -> &mut WriterBuilder
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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(()) }
pub fn has_headers(&mut self, yes: bool) -> &mut WriterBuilder
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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(()) }
pub fn flexible(&mut self, yes: bool) -> &mut WriterBuilder
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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(()) }
pub fn terminator(&mut self, term: Terminator) -> &mut WriterBuilder
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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(()) }
pub fn quote_style(&mut self, style: QuoteStyle) -> &mut WriterBuilder
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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(()) }
pub fn quote(&mut self, quote: u8) -> &mut WriterBuilder
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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(()) }
pub fn double_quote(&mut self, yes: bool) -> &mut WriterBuilder
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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(()) }
pub fn escape(&mut self, escape: u8) -> &mut WriterBuilder
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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(()) }
pub fn buffer_capacity(&mut self, capacity: usize) -> &mut WriterBuilder
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Set the capacity (in bytes) of the internal buffer used in the CSV writer. This defaults to a reasonable setting.
Trait Implementations
impl Debug for WriterBuilder
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fn fmt(&self, __arg_0: &mut Formatter) -> Result
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Formats the value using the given formatter. Read more
impl Default for WriterBuilder
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fn default() -> WriterBuilder
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Returns the "default value" for a type. Read more