学习官方示例 - System.RunError

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var P: Pointer;

procedure TForm1.Button1Click(Sender: TObject);
begin
  if P = nil then
    RunError(204);
end;

end.