How to convert float or currency to a localized string? - 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 Char1,2:
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

Delphi does provide a procedure called FloatToDecimal that converts floating point (e.g. Extended) and Currency values into a useful structure for further formatting. e.g.:
FloatToDecimal(..., 1234567890.1234, ...);
gives you:
TFloatRec
Digits: array[0..20] of Char = "12345678901234"
Exponent: SmallInt = 10
IsNegative: Boolean = True
Where Exponent gives the number of digits to the left of decimal point.
There are some special cases to be handled:
Exponent is zero
Digits: array[0..20] of Char = "12345678901234"
Exponent: SmallInt = 0
IsNegative: Boolean = True
means there are no digits to the left of the decimal point, e.g. .12345678901234
Exponent is negative
Digits: array[0..20] of Char = "12345678901234"
Exponent: SmallInt = -3
IsNegative: Boolean = True
means you have to place zeros in between the decimal point and the first digit, e.g. .00012345678901234
Exponent is -32768 (NaN, not a number)
Digits: array[0..20] of Char = ""
Exponent: SmallInt = -32768
IsNegative: Boolean = False
means the value is Not a Number, e.g. NAN
Exponent is 32767 (INF, or -INF)
Digits: array[0..20] of Char = ""
Exponent: SmallInt = 32767
IsNegative: Boolean = False
means the value is either positive or negative infinity (depending on the IsNegative value), e.g. -INF
We can use FloatToDecimal as a starting point to create a locale-independent string of "pictures codes".
This string can then be passed to appropriate Windows GetNumberFormat or GetCurrencyFormat functions to perform the actual correct localization.
i wrote my own CurrToDecimalString and FloatToDecimalString which convert numbers into the required locale independent format:
class function TGlobalization.CurrToDecimalString(const Value: Currency): string;
var
digits: string;
s: string;
floatRec: TFloatRec;
begin
FloatToDecimal({var}floatRec, Value, fvCurrency, 0{ignored for currency types}, 9999);
//convert the array of char into an easy to access string
digits := PChar(Addr(floatRec.Digits[0]));
if floatRec.Exponent > 0 then
begin
//Check for positive or negative infinity (exponent = 32767)
if floatRec.Exponent = 32767 then //David Heffernan says that currency can never be infinity. Even though i can't test it, i can at least try to handle it
begin
if floatRec.Negative = False then
Result := 'INF'
else
Result := '-INF';
Exit;
end;
{
digits: 1234567 89
exponent--------^ 7=7 digits on left of decimal mark
}
s := Copy(digits, 1, floatRec.Exponent);
{
for the value 10000:
digits: "1"
exponent: 5
Add enough zero's to digits to pad it out to exponent digits
}
if Length(s) < floatRec.Exponent then
s := s+StringOfChar('0', floatRec.Exponent-Length(s));
if Length(digits) > floatRec.Exponent then
s := s+'.'+Copy(digits, floatRec.Exponent+1, 20);
end
else if floatRec.Exponent < 0 then
begin
//check for NaN (Exponent = -32768)
if floatRec.Exponent = -32768 then //David Heffernan says that currency can never be NotANumber. Even though i can't test it, i can at least try to handle it
begin
Result := 'NAN';
Exit;
end;
{
digits: .000123456789
^---------exponent
}
//Add zero, or more, "0"'s to the left
s := '0.'+StringOfChar('0', -floatRec.Exponent)+digits;
end
else
begin
{
Exponent is zero.
digits: .123456789
^
}
if length(digits) > 0 then
s := '0.'+digits
else
s := '0';
end;
if floatRec.Negative then
s := '-'+s;
Result := s;
end;
Aside from the edge cases of NAN, INF and -INF, i can now pass these strings to Windows:
class function TGlobalization.GetCurrencyFormat(const DecimalString: WideString; const Locale: LCID): WideString;
var
cch: Integer;
ValueStr: WideString;
begin
Locale
LOCALE_INVARIANT
LOCALE_USER_DEFAULT <--- use this one (windows.pas)
LOCALE_SYSTEM_DEFAULT
LOCALE_CUSTOM_DEFAULT (Vista and later)
LOCALE_CUSTOM_UI_DEFAULT (Vista and later)
LOCALE_CUSTOM_UNSPECIFIED (Vista and later)
}
cch := Windows.GetCurrencyFormatW(Locale, 0, PWideChar(DecimalString), nil, nil, 0);
if cch = 0 then
RaiseLastWin32Error;
SetLength(ValueStr, cch);
cch := Windows.GetCurrencyFormatW(Locale, 0, PWideChar(DecimalString), nil, PWideChar(ValueStr), Length(ValueStr));
if (cch = 0) then
RaiseLastWin32Error;
SetLength(ValueStr, cch-1); //they include the null terminator /facepalm
Result := ValueStr;
end;
The FloatToDecimalString and GetNumberFormat implementations are left as an exercise for the reader (since i actually haven't written the float one yet, just the currency - i don't know how i'm going to handle exponential notation).
And Bob's yer uncle; properly localized floats and currencies under Delphi.
i already went through the work of properly localizing Integers, Dates, Times, and Datetimes.
Note: Any code is released into the public domain. No attribution required.

Answer 2

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;