unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
var
  mstream:TMemoryStream;
procedure TForm1.FormCreate(Sender: TObject); //程序开始先创建一个准备要测试的文件
var
  list:TStringList;
begin
  list:=TStringList.Create;
  with list do
  begin
    Add('aaaaaaaa');
    Add('bbbbbbbb');
    Add('cccccccc');
    Add('dddddddd');
    SaveToFile('f:\temp\test.txt');
  end;
  list.Free;
  mstream:=TMemoryStream.Create;    {同时建立内存流}

end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  mstream.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  mstream.LoadFromFile('f:\temp\test.txt');
  Memo1.Lines.LoadFromStream(mstream);
end;

procedure TForm1.Button2Click(Sender: TObject); //用字符指针读取流中的内容
var
  pstr:PChar;
begin
  pstr:=mstream.Memory; {把字符指针指向内存流}
  ShowMessage(pstr[0]); {a; 第一个字符}
  ShowMessage(pstr[10]); {b; 这个第二行的第一个字符; 每行8个字再加换行与回车共10个字符}
  ShowMessage(pstr[20]); {c}
  ShowMessage(pstr[30]); {d}
end;

procedure TForm1.Button3Click(Sender: TObject);
var
  buffer:array[0..2] of Char;
begin
  mstream.Seek(0,soFromBeginning);
  {参数1: Offset 是偏移量;soFromBeginning: 以开始为基准, 此时参数 Offset 要 >= 0;
  如果读取的话那就是向后读取}
  mstream.Read(buffer,SizeOf(buffer));
  ShowMessage(buffer);      {aaa}

  mstream.Seek(10,soFromCurrent);  //soFromCurrent: 以当前位置为基准;
  mstream.Read(buffer,SizeOf(buffer));
  ShowMessage(buffer);      {bbb}

  mstream.Seek(20,soFromEnd);
  {soFromEnd: 以结束为基准; 此时参数 Offset 要 <= 0;
  如果读取的话那就是向前读取}
  mstream.Read(buffer,SizeOf(buffer));
  ShowMessage(buffer);      {bbb}

  mstream.Seek(30,soFromBeginning);
  mstream.Read(buffer,SizeOf(buffer));
  ShowMessage(buffer);      {ddd}
end;

end.