unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Memo2: TMemo;
    Button1: TButton;
    Button2: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
var
  mstream:TStream;    {声明一个流对象}
procedure TForm1.FormCreate(Sender: TObject);
begin
  mstream:=TMemoryStream.Create;
  {!!!!!!!TStream 是抽象类, 只能通过其子类实例化; 这里我们用了内存流来生成实例}
  Memo1.Lines.Text:='ABCDEFGHIJKLMNOPQRSTUVWXYZ';    {给 Memo1 个初始值}
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  mstream.Free;  {流释放时, 所用内存当然也会同时释放}
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Memo1.Lines.SaveToStream(mstream);     {把 Memo1 中的内容写入到流}

  ShowMessage(IntToStr(mstream.Size));   {26, 当前流的大小}
  ShowMessage(IntToStr(mstream.Position)); {26, 当前流的指针}
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  mstream.Position:=4;  {调整流的当前指针位置}
  Memo2.Lines.LoadFromStream(mstream);  {读出流中的内容到 Memo2}
    {
    现在 Memo2 中的内容应该是: EFGHIJKLMNOPQRSTUVWXYZ
    如果 Position 是 0, Memo2 读出的内容会是: ABCDEFGHIJKLMNOPQRSTUVWXYZ
    如果 Position 等于 Size, 在这里如果是 26, Memo2 就读不出什么了.
    }
end;

end.