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.
