How to convert float or currency to a localized string?

Question

In Delphi¹, using FloatToStrF or CurrToStrF will automatically use the DecimalSeparator character to represent a decimal mark. Unfortunately DecimalSeparator is declared in SysUtils as Char^1,2:

var 
  DecimalSeparator: Char;

While the LOCALE_SDECIMAL is allowed to be up to three characters:

Character(s) used for the decimal separator, for example, "." in "3.14" or "," in "3,14". The maximum number of characters allowed for this string is four, including a terminating null character.

This causes Delphi to fail to read the decimal separator correctly; falling back to assume a default decimal separator of ".":

DecimalSeparator := GetLocaleChar(DefaultLCID, LOCALE_SDECIMAL, '.');

On my computer, which is quite a character, this cause floating point and currency values to be incorrectly localized with a U+002E (full stop) decimal mark.

i am willing to call the Windows API functions directly, which are designed to convert floating point, or currency, values into a localized string:

• GetNumberFormat
• GetCurrencyFormat

Except these functions take a string of picture codes, where the only characters allowed are:

• Characters "0" through "9" (U+0030..U+0039)
• One decimal point (.) if the number is a floating-point value (U+002E)
• A minus sign in the first character position if the number is a negative value (U+002D)

What would be a good way¹ to convert a floating point, or currency, value to a string that obeys those rules? e.g.

• 1234567.893332
• -1234567

given that the local user's locale (i.e. my computer):

• might not use a - to indicate negative (e.g. --)
• might not use a . to indicate a decimal point (e.g. ,,)
• might not use the latin alphabet 0123456789 to represent digits (e.g. [removed arabic digits that crash SO javascript parser])

---

A horrible, horrible, hack, which i could use:

function FloatToLocaleIndependantString(const v: Extended): string;
var
   oldDecimalSeparator: Char;
begin
   oldDecimalSeparator := SysUtils.DecimalSeparator;
   SysUtils.DecimalSeparator := '.'; //Windows formatting functions assume single decimal point
   try
      Result := FloatToStrF(Value, ffFixed, 
            18, //Precision: "should be 18 or less for values of type Extended"
            9 //Scale 0..18.   Sure...9 digits before decimal mark, 9 digits after. Why not
      );
   finally
      SysUtils.DecimalSeparator := oldDecimalSeparator;
   end;
end;

---

Additional info on the chain of functions the VCL uses:

• FloatToStrF and CurrToStrF calls:
  • FloatToText calls:
    • FloatToDecimal

Note

• DecimalSeparator: Char, the single character global is deprecated, and replaced with another single character decimal separator

¹ in my version of Delphi
² and in current versions of Delphi

Answer 1

Ok, this may not be what you want, but it works with D2007 and up. Thread safe and all.

uses Windows,SysUtils;

var
  myGlobalFormatSettings : TFormatSettings;

// Initialize special format settings record
GetLocaleFormatSettings( 0,myGlobalFormatSettings);
myGlobalFormatSettings.DecimalSeparator := '.';


function FloatToLocaleIndependantString(const value: Extended): string;
begin
  Result := FloatToStrF(Value, ffFixed, 
        18, //Precision: "should be 18 or less for values of type Extended"
        9, //Scale 0..18.   Sure...9 digits before decimal mark, 9 digits after. Why not
        myGlobalFormatSettings
  );
end;