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
{$R *.dfm}
var
mStream: TStream;
{声明一个流对象}
procedure TForm1.FormCreate(Sender: TObject);
begin
mStream := TMemoryStream.Create;{TStream 是抽象类, 只能通过其子类实例化; 这里我们用了内存流来生成实例}
Memo1.Lines.Text :='ABCDEFGHIJKLMNOPQRSTUVWXYZ';{给 Memo1 个初始值}
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
Memo1.Lines.SaveToStream(mStream); {把 Memo1 中的内容写入到流}
ShowMessage(IntToStr(mStream.Size)); {26, 当前流的大小}
ShowMessage(IntToStr(mStream.Position));{26, 当前流的指针}
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
mStream.Position :=4; {调整流的当前指针位置}
Memo2.Lines.LoadFromStream(mStream);
{读出流中的内容到 Memo2}{ 现在 Memo2 中的内容应该是: EFGHIJKLMNOPQRSTUVWXYZ 如果 Position 是 0,memo2 读出的内容会是: ABCDEFGHIJKLMNOPQRSTUVWXYZ 如果 Position 等于 Size, 在这里如果是 26, Memo2 就读不出什么了. }
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
mStream.Free;{流释放时, 所用内存当然也会同时释放}
end;
end.
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内存流读取文件
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;
type
TForm1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
Button2: TButton;
Button3: TButton;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
end;
var
Form1: TForm1;
implementation{$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:
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分类参数说明打开
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读写打开共
享
模
式fmShareCompat共享模式, 兼容 DosfmShareExclusive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
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遍历读取流中的所有数据unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;typeTForm1 = 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;varForm1: TForm1;implementation{$R *.dfm}//先制造一个测试文件 procedure TForm1.FormCreate(Sender: TObject);varstrList: TStringList;beginstrList := TStringList.Create;strList.Add('ABCDEFGHIJKLMNOPQRSTUVWXYZ');strList.SaveToFile('c:\temp\test.txt'); strList.Free;end;procedure TForm1.Button1Click(Sender: TObject);var ms: TMemoryStream; c: Char; s1,s2: string;begin ms := TMemoryStream.Create;ms.LoadFromFile('c:\temp\test.txt');{读入内存流} s1 :=''; s2 :='';ms.Position :=0; {指针到开始} while ms.Position < ms.Sizedo {循环读出} begin ms.Read(c,1); {每读出一个字节, 指针会自动移到新的位置} s1 := s1 + c +' '; {用文本记录} s2 := s2 + IntToHex(Byte(c),2) +' ';{用两位数的十六进制记录} end;Memo1.Lines.Text := s1; Memo2.Lines.Text := s2;{Memo1 会显示: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z }{Memo2 会显示: 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 56 57 58 59 5A 0D 0A} ms.Free;end;end.序列化unit Unit1;interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;type TForm1 = class(TForm) Button1: TButton; Button2: TButton; Button3: TButton; Button4: TButton; Memo1: TMemo; procedure Button1Click(Sender: TObject); procedure Button2Click(Sender: TObject);procedure Button3Click(Sender: TObject);procedure Button4Click(Sender: TObject);private { Private declarations } public { Public declarations } end;var Form1: TForm1;implementation {$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);varstream: TStream;const strPath ='c:\temp\m.dat';beginstream := 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.