[Lazarus] UTF8 RTL for Windows

[Mattias Gaertner]

On Sat, 22 Nov 2014 14:37:00 +0100
Jürgen Hestermann <juergen.hestermann at gmx.de> wrote:

> Am 2014-11-20 um 17:21 schrieb Mattias Gaertner:
>  > The development version of FPC 2.7.1 has extended Strings and many RTL
>  > functions now work for codepages other than the system codepage.
> ....
>  > 2. The new mode: The LCL, FCL and RTL treat all "String" as UTF-8 encoded.
> ...
>  > When accessing the WinAPI you must use the W functions or use
>  > UTF8ToWinCP and WinCPToUTF8.
> 
> Is this correct?
> The W functions of the WinAPI expect UTF16 so
> a conversion needs to be done in both cases,
> either to System code page or to UTF16.
> Or can we use STRING with WinAPI W functions directly?

You can use them directly.

For example:

procedure TForm1.FormCreate(Sender: TObject);
var
  s: string; // String = AnsiString because of $H+
begin
  s:=GetCommandLineW;
  // GetCommandLineW returns a UTF-16 PWideChar
  // the compiler adds code to convert this to the
  // default system codepage (CP_ACP = CP_UTF8)
  // the resulting string has StringCodePage CP_ACP
  // and is encoded in UTF-8.
  // therefore you can simply use it with the LCL
  Memo1.Lines.Add(s);
end;

You will get a compiler warning (id 4105), that WideString to Ansistring
might loose data. The warning is right if the default string codepage is
not UTF-8. If your code only runs with the RTL in UTF-8 mode, you
can disable this warning.
As alternative you can use:
  s:=UTF8Encode(GetCommandLineW);

You must also use UTF8Encode if your code should run with both FPC 2.6.4
and 2.7.1.

Mattias