Numbers, Currencies, and NumberFormatInfo

Numbers and currencies follow a similar pattern to date/times and DateTime FormatInfo, but without the additional complexity of calendars:

• Numbers and currencies are formatted using the NumberFormatInfo class.

• The CultureInfo class has a NumberFormatInfo property called NumberFormat.

• It is possible to build your own culture-unaware format strings from primitives such as #, the comma, the period, and zero (e.g., "###,###.00").

• It is possible to specify culture-aware formats (see Table 6.16) using a format specifier, which draws on information in a NumberFormatInfo object.

  Table 6.16. Standard Number Format Specifiers

  Format Specifier	Name	Uses NumberFormatInfo
  c, C	Currency	Yes
  d, D	Decimal	No
  e, E	Exponential (Scientific)	No
  f, F	Fixed point	Yes
  g, G	General	No
  n, N	Number	Yes
  p, P	Percent	Yes
  r, R	Round-trip	No
  x, X	Hexadecimal	No

  
  

• Number types that overload ToString methods accept an IFormatProvider that can be either a NumberFormatInfo or a CultureInfo (from which the NumberFormatInfo is extracted) .

• The FxCop "Specify IFormatProvider" rule catches number types that overload ToString methods, which are not called with an IFormatProvider.

As we saw with date/times, it should be obvious by now that predicting the myriad cultural differences across the world is very difficult, but to remove any doubt, have a look at the examples in Table 6.17, which show the number 20000.15 formatted for currency in a selection of different cultures. Notice the use of commas and periods to indicate sometimes a thousands separator and a decimal separator, and sometimes vice versa; the positioning of the currency symbol; the positioning of the negative sign; the expression of negatives using parentheses; and the exclusion of decimals altogether.

Table 6.17. Examples of Formatted Currencies

Culture Name	Culture DisplayName	Example Formatted Currency
ar-SA	Arabic (Saudi Arabia)	20,000.15.
bg-BG	Bulgarian (Bulgaria)	-20 000,15
ca-ES	Catalan (Catalan)	-20.000,15 €
zh-CN	Chinese (People's Republic of China)	-20,000.15
zh-HK	Chinese (Hong Kong S.A.R.)	(HK$20,000.15)
da-DK	Danish (Denmark)	kr -20.000,15
de-DE	German (Germany)	-20.000,15 €
de-AT	German (Austria)	-€ 20.000,15
en-US	English (United States)	($20,000.15)
en-GB	English (United Kingdom)	-£20,000.15
es-AR	Spanish (Argentina)	$-20.000,15
es-CL	Spanish (Chile)	-$ 20.000,15
ja-JP	Japanese (Japan)	-¥20,000
id-ID	Indonesian (Indonesia)	(Rp20.000)