Converting a hex string representation of a widechar codepoint to a widechar in Delphi

Question

I am having trouble converting text within an edit box to a WideChar. This is being used in code for printing emoji characters.

If I manually set the WideChar values like the following it works

Emoji[1] := WideChar($D83D);
Emoji[2] := WideChar($DC4D);

But I want to be able to set the hex codes via edit boxes as follows

StringToWideChar(edit1.text, @wc1, Length(edit1.text));
StringToWideChar(edit2.text, @wc2, Length(edit2.text));
Emoji[1] := wc1;
Emoji[2] := wc2;

wc1 and wc2 are defined as WideChar. The edit boxes contain the same values as are hard coded above. That code results in a blank output, so something is wrong with the conversion.

What am I doing wrong? Thanks for any help here.

Answer 1

You mustn't interpret the string '$D83D' as text -- instead, you must parse it as an integer.

First, you need to obtain the text from the edit box. This is Edit1.Text. Then you need to convert this to an integer. For instance, you can use StrToInt or TryStrToInt. Then you simply need to reinterpret (cast) this integer as a Char:

procedure TForm1.Edit1Change(Sender: TObject);
var
  CodeUnit: Integer;
begin
  if TryStrToInt(Edit1.Text, CodeUnit) and InRange(CodeUnit, 0, $FFFF) then
    Label1.Caption := Char(CodeUnit)
  else
    Label1.Caption := '';
end;

Here, as a bonus, I also validate that the supposed codeunit is an actual 16-bit unsigned integer using InRange (I mean, the user could in theory type 123456789). Delphi's StrToInt functions support hex using the dollar sign notation.