Make VarToDoubleAsString use Delphi settings (not OS settings)

Question

When one assigns a Variant containing a string value to a floating point variable, Delphi calls VarToDoubleAsString to convert, which in turn uses the OS settings for decimal and thousandth separators (via VarR8FromStr). This is problematic if you need to change SysUtils.DecimalSeparator and SysUtils.ThousandSeparator . For example, run the following program:

 program VarStrToFloat; {$APPTYPE CONSOLE} uses SysUtils, Math; function FormatFloatUsingDelphiSettings(Value: Extended): string; begin Result := FormatFloat('#,##0.00', Value); end; procedure Test(const AMsg: string); var r1, r2: Extended; s1, s2: string; v: Variant; begin r1 := 5432.1; s1 := FormatFloatUsingDelphiSettings(r1); v := s1; // <== conversion uses OS settings r2 := v; s2 := FormatFloatUsingDelphiSettings(r2); Write(AMsg: 8, s1: 10, s2: 10, ' '); if SameValue(r1, r2) then Writeln('OK') else Writeln('FAIL'); end; procedure SwapEm; var tmp: Char; begin tmp := DecimalSeparator; DecimalSeparator := ThousandSeparator; ThousandSeparator := tmp; end; begin Test('Default'); SwapEm; Test('Changed'); Readln; end. 

The first test is working fine, the second is unsuccessful.

Can I use the Variant transformation SysUtils.DecimalSeparator and SysUtils.ThousandSeparator ?

Answer 1

You can replace the VarR8FromStr function in varutils.pas to your liking, and VarToDoubleAsString will use it instead:

 function MyConversion(const strIn: WideString; LCID: Integer; dwFlags: Longint; out dblOut: Double): HRESULT; stdcall; const CResult: array [False..True] of HRESULT = (VAR_INVALIDARG, VAR_OK); var s: string; begin s := StringReplace(StrIn, ThousandSeparator, '', [rfReplaceAll]); Result := CResult[TryStrToFloat(s, dblOut)]; end; [...] begin varutils.VarR8FromStr := MyConversion; [...]