Delphi 中流的使用

所谓"流", 就是一段数据或是一块内存;
在进行流操作时, 我们不必关心流中的数据到底是什么; 只需要知道流的大小和当前的指针位置. 所以流只有两个属性:
Size、Position.
对流的操作, 不过就是读取和写入. 所以流最主要的方法就是 Read 和 Write.
在很多控件的使用中, 读取主要用 LoadFromStream; 写入主要用 SaveToStream.

TMemoryStream(内存流) 入门
举个例子: (建立新工程, 添加两个 Memo、两个 Button)

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 Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

procedure FormDestroy(Sender: TObject);

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.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;

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;

end.

 

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.

TFileStream读写

TStream 是一个抽象的基类, 不能直接生成对象. 在具体的应用中, 主要使用它的子孙类:

TFileStream: 文件流

TStringStream: 字符串流

TMemoryStream: 内存流

TResourceStream: 资源文件流

THandleStream: 是 TFileStream 的父类、

TStream 的子类TCustomMemoryStream: 是 TMemoryStream 和 TResourceStream 的父类、

TStream 的子类与流相关的常用类还有: TReader、TWriter、TCompressionStream、TDecompressionStream

来一个文件流的例子:

procedure TForm1.Button1Click(Sender: TObject);

var

getStream,setStream: TFileStream; {声明一个文件流}

getPath,setPath:string;

begin

getPath := 'c:\temp\get.jpg';{需要这个文件存在}

setPath :='c:\temp\set.jpg';{这个会自动建立}

ifnot FileExists(getPath)then

begin

ShowMessage('找不到我们要测试的图片文件: ' + getPath);

Exit;

end;

getStream := TFileStream.Create(getPath, fmOpenReador fmShareExclusive);

setStream := TFileStream.Create(setPath, fmCreate);{建立文件流需要两个参数: 参数 1 是路径, 参数 2 是打开模式}

getStream.Position :=0;{流指针移到开始, 复制时从这里开始}

setStream.CopyFrom(getStream, getStream.Size);{Copy 流}{CopyFrom 的参数 2 是要复制的内容大小; 如果为 0 , 不管指针在什么位置都会复制所有内容}{CopyFrom 返回实际拷贝的字节数}

{这时硬盘上就有 set.jpg 文件, 与 get.jpg 一么一样}{其实就是复制文件, 不过这里我们是用文件流实现的}

getStream.Free;

setStream.Free;

end;

TFileStream 打开模式与共享模式:

 

分类 参数 说明 打
开
模
式 共
享
模
式

fmCreate	建立文件, 如果存在则打开它。
fmOpenRead	只读打开
fmOpenWrite	只写打开
fmOpenReadWrite	读写打开
fmShareCompat	共享模式, 兼容 Dos
fmShareExclusive	不允许别人以任何方式打开
fmShareDenyWrite	允许别人以只写方式打开
fmShareDenyRead	允许别人以只读方式打开
fmShareDenyNone	允许别人以任何方式打开

 

遍历读取流中的所有数据

unit Unit1;

interface

uses

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

type

TForm1 = class(TForm)

Memo1: TMemo;

Memo2: TMemo;{需要添加两个 Memo 用于显示}

Button1: TButton;

procedure Button1Click(Sender: TObject);

procedure FormCreate(Sender: TObject);

end;

var

Form1: TForm1;

implementation

{$R *.dfm}//先制造一个测试文件

procedure TForm1.FormCreate(Sender: TObject);

var

strList: TStringList;

begin

strList := TStringList.Create;

strList.Add('ABCDEFGHIJKLMNOPQRSTUVWXYZ');

strList.SaveToFile('c:\temp\test.txt'); strList.Free;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

ms: TMemoryStream;

c: Char; s1,s2: string;

begin

ms := TMemoryStream.Create;

ms.LoadFromFile('c:\temp\test.txt');{读入内存流}

s1 :=''; s2 :='';

ms.Position :=0; {指针到开始}

while ms.Position < ms.Sizedo {循环读出}

begin

ms.Read(c,1); {每读出一个字节, 指针会自动移到新的位置}

s1 := s1 + c +' '; {用文本记录}

s2 := s2 + IntToHex(Byte(c),2) +' ';{用两位数的十六进制记录}

end;

Memo1.Lines.Text := s1;

Memo2.Lines.Text := s2;{Memo1 会显示: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z }{Memo2 会显示: 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 56 57 58 59 5A 0D 0A}

ms.Free;

end;

end.

序列化

unit Unit1;

interface

uses

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

type

TForm1 = class(TForm)

Button1: TButton;

Button2: TButton;

Button3: TButton;

Button4: TButton;

Memo1: TMemo;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

procedure Button3Click(Sender: TObject);

procedure Button4Click(Sender: TObject);

private { Private declarations }

public { Public declarations }

end;

var

Form1: TForm1;

implementation

{$R *.dfm}//添加一个 Memo1 然后修改其内容

procedure TForm1.Button1Click(Sender: TObject);

begin

WriteComponentResFile('c:\temp\memo.dat', Memo1);{只此一句就可以把当前的 Memo 的状态序列化到文件}

end;

//反序列化, 读回

procedure TForm1.Button2Click(Sender: TObject);

begin

ReadComponentResFile('c:\temp\memo.dat', Memo1);{一句话就可以读回, 不管是经过了什么操作(甚至是关机)}

end;{ 这好像和流没什么关系, 其实这就是流的典型操作, WriteComponentResFile 和 ReadComponentResFile 分别调用了流类的 WriteComponentRes 与 ReadComponentRes 方法. 下面用更直接的流的方式重新实现一次:}

//序列化

procedure TForm1.Button3Click(Sender: TObject);

var

stream: TStream;

const strPath ='c:\temp\m.dat';

begin

stream := TFileStream.Create(strPath, fmCreate);

stream.WriteComponentRes(Memo1.ClassName, Memo1);{WriteComponentRes 有两个参数: 文件名和组件名}

stream.Free;

end;

//反序列化

procedure TForm1.Button4Click(Sender: TObject);

var

stream: TStream;

const strPath ='c:\temp\m.dat';

begin

stream := TFileStream.Create(strPath, fmOpenRead);

stream.ReadComponentRes(Memo1);{ReadComponentRes 只有一个参数: 组件名}

stream.Free;

end;

end.

用流读写结构化文件

unit Unit1;

interface

uses

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

type

TForm1 = class(TForm)

Memo1: TMemo; {添加 Memo 显示内容}

Button1: TButton;

Button2: TButton;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

private { Private declarations }

public { Public declarations }

end;

var

Form1: TForm1;

implementation

{$R *.dfm}

type

TRec = record {定义一个记录}

name:string[8];

age: Word;

end;//写入

procedure TForm1.Button1Click(Sender: TObject);

var

rec: TRec;

ms: TMemoryStream;

begin

ms := TMemoryStream.Create;

rec.name := '张三';

rec.age :=8;

ms.Write(rec, SizeOf(rec));

rec.name :='李四';

rec.age :=81;

ms.Write(rec, SizeOf(rec));

rec.name :='王二麻子';

rec.age :=18;

ms.Write(rec, SizeOf(rec));

ms.SaveToFile('c:\temp\rec.dat');

ms.Free;

end;

//读取

procedure TForm1.Button2Click(Sender: TObject);

var

rec: TRec;

ms: TMemoryStream;

begin

ms := TMemoryStream.Create;

ms.LoadFromFile('c:\temp\rec.dat');

Memo1.Clear;

ms.Position :=0;

while ms.Position < ms.Sizedo

begin

ms.Read(rec, SizeOf(rec));

Memo1.Lines.Add(rec.name +' ' + IntToStr(rec.age));

end;{Memo1 的显示结果会是: 张三 8 李四 81 王二麻子 18 }

ms.Free;

end;

end.

压缩与解压缩

unit Unit1;

interface

uses

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

type

TForm1 = class(TForm)

Button1: TButton;

Button2: TButton;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

end;

var

Form1: TForm1;

implementation

{$R *.dfm}

uses

Zlib; {压缩流 TCompressionStream 与解压缩流 TDecompressionStream 来自 Zlib 单元}//压缩

procedure TForm1.Button1Click(Sender: TObject);

var

cs: TCompressionStream;{定义压缩流}

fs,ms:TMemoryStream;{fs 是要压缩的流; ms 是接收压缩后文件的流}

num: Integer; {原始文件大小}

begin{第一步: 调入要压缩的文件, 并获取大小}

fs := TMemoryStream.Create;

fs.LoadFromFile('c:\temp\test.txt');{文件要存在啊}

num := fs.Size;{第二步: 建立接收的流, 并先写入原始文件大小}

ms := TMemoryStream.Create;

ms.Write(num, SizeOf(num));{第三步: 压缩}

cs := TCompressionStream.Create(clMax, ms);{参数1是压缩比; 参数2是接收流}

fs.SaveToStream(cs);{传入要压缩的数据}

cs.Free; {压缩流 Free 后才真正完成压缩, 所以提前 Free}{第四步: 保存}

ms.SaveToFile('c:\temp\test.zipx');{第五步: 释放}

ms.Free; fs.Free;{压缩比参数: clNone 无压缩 clFastest 快速 clDefault 默认 clMax 最大比例}

end;

//解压缩

procedure TForm1.Button2Click(Sender: TObject);

var

ds: TDecompressionStream;{解压流}

fs,ms: TMemoryStream; {fs 是准备要解压的流; ms 是接受解压数据的流}

num: Integer; {接受文件压缩前的大小}

begin{第一步: 准要解压的文件}

fs := TMemoryStream.Create;

fs.LoadFromFile('c:\temp\test.zipx');{必须是上一个压缩方法生成的文件}{第二步: 读出文件压缩前的大小}

fs.Position :=0; fs.ReadBuffer(num,SizeOf(num));{第三步: 准备好要接收的流, 并设置需要的大小}

ms := TMemoryStream.Create; ms.SetSize(num);{第四步: 解压}

ds := TDecompressionStream.Create(fs);{参数是要解压的流}{第五步: 把解压后的数据读出存放到已准备好接收的流}

ds.Read(ms.Memory^, num);{第六步: 保存}

ms.SaveToFile('c:\temp\test2.txt');

ds.Free;

ms.Free;

fs.Free;

end;

end.

压缩与解压缩的函数

unit Unit1;

interface

uses

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

type

TForm1 = class(TForm)

Button1: TButton;

Button2: TButton;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

end;

var

Form1: TForm1;

implementation

{$R *.dfm}

uses

Zlib;//压缩函数

procedure Zip(var fs: TMemoryStream);

var

cs: TCompressionStream;

ms: TMemoryStream;

num: Integer;

begin

ifnot(Assigned(fs)and (fs.Size>0))then

Exit;

num := fs.Size;

ms := TMemoryStream.Create;

cs := TCompressionStream.Create(clMax, ms);

try

fs.SaveToStream(cs);

cs.Free; //ms.Position := 0;

fs.Clear;

fs.WriteBuffer(num, sizeof(num));

fs.CopyFrom(ms,0);

finally

ms.Free;

end;

end;

//解压函数

procedure UnZip(var fs: Tmemorystream);

var

ds: TDecompressionStream;

ms: TMemoryStream;

num: Integer;

begin

ifnot(Assigned(fs)and (fs.Size>0))then

Exit;

fs.Position :=0;

fs.ReadBuffer(num,sizeof(num));

ms := TMemoryStream.Create;

ds := TDecompressionStream.Create(fs);

try

ms.SetSize(num);

ds.Read(ms.Memory^, num); //ms.Position := 0;

fs.Clear;

fs.CopyFrom(ms,0);

finally

ds.Free;

ms.Free;

end;

end;

//压缩测试

procedure TForm1.Button1Click(Sender: TObject);

var

ms: TMemoryStream;

begin

ms := TMemoryStream.Create;

ms.LoadFromFile('c:\temp\test.txt');

Zip(ms);

ms.SaveToFile('c:\temp\test.zipx');

end;

//解压测试

procedure TForm1.Button2Click(Sender: TObject);

var

ms: TMemoryStream;

begin

ms := TMemoryStream.Create;

ms.LoadFromFile('c:\temp\test.zipx');

UnZip(ms);

ms.SaveToFile('c:\temp\test2.txt');

end;

end.

分割与合并文件函数

unit Unit1;

interface

uses

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

type

TForm1 = class(TForm)

Button1: TButton;

Button2: TButton;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

end;

var

Form1: TForm1;

implementation

{$R *.dfm}//分割文件的函数{参数 1 是要分割的文件名; 参数 2 是要风格文件的大小, 单位是 KB}{分割后的文件名扩展名用序号替换}

function SplitFile(const FileName:string; Size: Cardinal): Boolean;

var

fStream: TFileStream;{原始文件}

toStream: TMemoryStream;{分文件}

p,i: Integer; {p 记录当前指针位置; i 记录这是第几个分的文件}

begin

Result := False;

Size := Size * 1024; {把大小的单位转换为字节}

fStream := TFileStream.Create(FileName, fmOpenRead);

p :=0;

i :=0;

toStream := TMemoryStream.Create;

while p < fStream.Size do

begin

toStream.Clear; {清空上次数据}

fStream.Position := p;{放好指针位置}

if fStream.Size-p < Sizethen

Size := fStream.Size-p;{最后一个时, 有多少算多少}

toStream.CopyFrom(fStream, Size);{复制}

toStream.SaveToFile(FileName +'.' + IntToStr(i)); {保存}

Inc(i);

p := p + Size;

end;

fStream.Free;

toStream.Free;

Result := True;

end;

//合并文件, 参数是其中一个分文件名

function MergeFile(const FileName:string):Boolean;

var

ms: TMemoryStream; {读取分文件}

fs: TFileStream;{合并后的文件}

path:string;

i: Integer;

begin

path := ChangeFileExt(FileName,'');{去掉序号扩展名}

ShowMessage(path);

i :=0;

ms := TMemoryStream.Create;

fs := TFileStream.Create(path, fmCreate);

while FileExists(path +'.' + IntToStr(i))do

begin

ms.LoadFromFile(path +'.' + IntToStr(i));

fs.CopyFrom(ms,0);{TFileStream 不需要 SetSize; 但如果用 TMemoryStream 就需要}

Inc(i);

end;

ms.Free;

fs.Free;

end;

//测试分割

procedure TForm1.Button1Click(Sender: TObject);

begin

SplitFile('c:\temp\test.txt',10);

end;

//测试合并

procedure TForm1.Button2Click(Sender: TObject);

begin

MergeFile('c:\temp\test.txt.0');

end;

end.