Configuring CSV parsing and writing

CSV is not a well-defined format. It doesn’t have a specification and there are many variants.

Package encoding/csv supports most common CSV formats and allows tweaking reading and writing process.

Configuring CSV Reader

After you create csv.Reader with csv.NewReader(), you can set the following fields to change the behavior.

Comma

Most CSV files use , to separate records but other characters are used too. If you have a file that uses ; as a separator you can configure a reader with r.Comma = ';'.

Comment

If you want to treat some CSV as comments and ignore them during reading, you can set a comment character.

For example if CSV file is:

# Comment
2013-02-08,15.07,AAL

you can ignore comment lines by setting r.Comment = '#'.

By default CSV reader doesn’t detect comments and will return an error trying to parse comment line.

FieldsPerRecord

Each line in a CSV file (a record) can have a different number of fields.

If you know that e.g. CSV file you’re parsing always has 5 fields in each record (line) then set r.FieldsPerRecord = 5. Read() will return an error if there’s a mismatch.

If you don’t know how many fields there are but know that it’s always the same number, use r.FieldsPerRecord = 0. This is a default so you don’t have to do it explicitly.

In that case csv.Reader will use the first line to detect number of fields and will return an error if subsequent records have a different number of fields.

If you want to allow a variable number of fields per record, set r.FieldsPerRecord = -1.

LazyQuotes

By default false.

If true, csv.Reader is more lax about parsing of quoted values i.e. a quote may appear in an unquoted field and a non-doubled quote may appear in a quoted field.

TrimLeadingSpace

By default false.

If true, csv.Reader leading white space in a field is ignored.

ReuseRecord

By default false.

If true, the []string slice returned by Read() might be re-used across Read() calls.

This is faster but you have to be more careful when using the result.

Configuring CSV writer

After you create csv.Writer with csv.NewWriter(), you can set the following fields to change the behavior.

Comma

Field delimiter, , by default.

UseCRLF

False by default.

If true, uses Windows style line terminator (CRLF i.e. \r\n).

By default uses Unix style line terminator (LF i.e. \n).