procedure TForm1.Button1Click(Sender: TObject);
var DC: HDC;
    dwTable: DWORD;
    dwOffset: DWORD;
    Buffer: PChar;
    cbData: DWORD;
    Size: DWORD;
begin
  DC := GetDC(ComboBox1.Handle);

  Size := GetTextFace(DC, Size, nil);
  if size = 0 then
     begin
       ShowMessage(SysErrorMessage(GetLastError));
       exit;
     end;
  GetMem(Buffer, Size);
  GetTextFace(DC, Size, Buffer);
  Label1.Caption := Buffer;

  ReleaseDC(ComboBox1.Handle, DC);
end;