关于 Delphi 中流的使用，3 通过内存流读取文件

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);

//程序开始先创建一个准备要测试的文件

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;

{同时建立内存流}

mStream := TMemoryStream.Create;

end;

procedure TForm1.Button1Click(Sender: TObject);

//通过流读文件到 Memo

begin

mStream.LoadFromFile('c:\temp\test.txt'); {把文件读入内存流}

Memo1.Lines.LoadFromStream(mStream); {把内存流载入 Memo1}

end;

procedure TForm1.Button2Click(Sender: TObject);

//用字符指针读取流中的内容

var

pc: PChar;

begin

pc := mStream.Memory; {把字符指针指向内存流}

ShowMessage(pc[0]); {a; 第一个字符}

ShowMessage(pc[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(pc[20]); {c}

ShowMessage(pc[30]); {d}

end;

procedure TForm1.Button3Click(Sender: TObject);

//从流读入到缓冲区

var

buffer: array[0..2] of Char; {定义个字符缓冲区}

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}

{关于 Seek 函数:

参数1: Offset 是偏移量;

参数2: Origin 是指针的基准位置, 有三个选值: soFromBeginning、soFromCurrent、soFromEnd

soFromBeginning: 以开始为基准, 此时参数 Offset 要 >= 0;

soFromCurrent: 以当前位置为基准;

soFromEnd: 以结束为基准; 此时参数 Offset 要 <= 0;

返回: 指针新位置

}

end;

procedure TForm1.FormDestroy(Sender: TObject);

begin

mStream.Free;

end;

end.