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);
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

var
 mStream: TMemoryStream;

procedure TForm1.FormCreate(Sender: TObject);
//程式開始先建立一個準備要測試的檔案
var
 strList: TStringList;
begin
 

 strList := TStringList.Create;
 strList.Add('aaaaaaaa');
 strList.Add('bbbbbbbb');
 strList.Add('cccccccc');
 strList.Add('dddddddd');
 strList.SaveToFile('c:\temp\test.txt');
 strList.Free;

 {同時建立記憶體流}
 mStream := TMemoryStream.Create;
end;


procedure TForm1.Button1Click(Sender: TObject);
//通過流讀檔案到 Memo
 

begin
 mStream.LoadFromFile('c:\temp\test.txt'); {把檔案讀入記憶體流}
 Memo1.Lines.LoadFromStream(mStream);   {把記憶體流載入 Memo1}
end;


procedure TForm1.Button2Click(Sender: TObject);
//用字元指標讀取流中的內容
var
 pc: PChar;
begin
 pc := mStream.Memory; {把字元指標指向記憶體流}
 ShowMessage(pc[0]);  {a; 第一個字元}
 ShowMessage(pc[10]); {b; 這個第二行的第一個字元; 每行8個字再加換行與回車共10個字元}
 ShowMessage(pc[20]); {c}
 ShowMessage(pc[30]); {d}
end;


procedure TForm1.Button3Click(Sender: TObject);
//從流讀入到緩衝區
var
 buffer: array[0..2] of Char; {定義個字元緩衝區}
begin
 mStream.Seek(0, soFromBeginning);
 mStream.Read(buffer, SizeOf(buffer));
 ShowMessage(buffer); {aaa}

 mStream.Seek(10, soFromBeginning);
 mStream.Read(buffer, SizeOf(buffer));
 ShowMessage(buffer); {bbb}

 mStream.Seek(20, soFromBeginning);
 mStream.Read(buffer, SizeOf(buffer));
 ShowMessage(buffer); {ccc}

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

{關於 Seek 函式:
 引數1: Offset 是偏移量;
 引數2: Origin 是指標的基準位置, 有三個選值: soFromBeginning、soFromCurrent、soFromEnd
     soFromBeginning: 以開始為基準, 此時引數 Offset 要 >= 0;
     soFromCurrent: 以當前位置為基準;
     soFromEnd: 以結束為基準; 此時引數 Offset 要 <= 0;
 返回: 指標新位置
}
end;


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

end.