var
Form5: TForm5;
{$DEFINE WANYI}
implementation
{$R *.dfm}
procedure TForm5.Button1Click(Sender: TObject);
begin
{$IFDEF WanYi}
ShowMessage(‘标识符 WanYi 已定义‘);
{$ELSE}
ShowMessage(‘标识符 WanYi 未定义‘);
{$ENDIF}
end;
原文：https://www.cnblogs.com/bwdblogs/p/10852402.html