CSV

Quoting Rules

• Fields containing comma, quote, or newline MUST be wrapped in double quotes
• Double quotes inside quoted fields escape as

  ""

  (two quotes), not backslash
• Unquoted fields with leading/trailing spaces—some parsers trim, some don't; quote to preserve
• Empty field

  ,,

  vs empty string

  ,"",

  —semantically different; be explicit

Delimiters

• CSV isn't always comma—detect

  ;

  (European Excel),

  \t

  (TSV),

  |

  in legacy systems
• Excel exports use system locale delimiter; semicolon common in non-US regions
• Sniff delimiter from first line but verify—header might not contain special chars

Encoding

• UTF-8 BOM (

  0xEF 0xBB 0xBF

  ) breaks naive parsers but Excel needs it for UTF-8 detection
• When generating for Excel on Windows: add BOM; for programmatic use: omit BOM
• Latin-1 vs UTF-8 ambiguity—explicitly declare or detect encoding before parsing

Common Parsing Failures

• Newlines inside quoted fields are valid—don't split on

  \n

  before parsing
• Unescaped quote in middle of field corrupts rest of file—validate early
• Trailing newline at EOF—some parsers create empty last row; strip or handle
• Inconsistent column count per row—validate all rows match header count

Numbers & Dates

• 1,234.56

  vs

  1.234,56

  —locale-dependent; standardize or document format
• Dates: ISO 8601 (

  2024-01-15

  ) only unambiguous format;

  01/02/24

  is chaos
• Leading zeros in numeric fields (

  007

  )—quote to preserve or document as string

Excel Quirks

• Formula injection: fields starting with

  =

  ,

  +

  ,

  -

  ,

  @

  execute as formulas—prefix with

  '

  or tab
• Long numbers (>15 digits) lose precision—quote and format as text
• Scientific notation triggered by

  E

  in numbers—quote if literal text needed