关于使用MAPVIEWOFFILE大文件的读写(DELPHI版)

unit filemap;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;

const

    fileName = 'myTest.txt';

type

  TForm1 = class(TForm)

    btnUpper: TButton;

    btnLower: TButton;

    txtContent: TMemo;

    Label1: TLabel;

    btnClose: TButton;

    procedure FormCreate(Sender: TObject);

    procedure btnUpperClick(Sender: TObject);

    procedure btnLowerClick(Sender: TObject);

    procedure btnCloseClick(Sender: TObject);

  private

    { Private declarations }

  public

    UCase:Boolean;

    procedure ChangeFileCase;

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



// 全文中的txtContent.Lines.LoadFromFile(fileName)其目的只是为了显示文件修改结果



procedure TForm1.FormCreate(Sender: TObject);

begin

    txtContent.Clear();

    txtContent.Lines.LoadFromFile(fileName);

    //缺省将其转变为大写

    UCase := True;

end;



procedure TForm1.btnUpperClick(Sender: TObject);

begin

    UCase := true;

    ChangeFileCase;

end;



procedure TForm1.btnLowerClick(Sender: TObject);

begin

    UCase := false;

    ChangeFileCase;

end;



procedure Tform1.ChangeFileCase;//这个是本示例文件的核心运算部分

var

    FFileHandle : THandle;

    FMapHandle : THandle;

    FFileSize : Integer;

    FData : PByte;

    PData : PChar;

begin

//-------------------1 判断文件是否存在----------------------//

    if not FileExists(fileName) then

        raise Exception.Create('文件不存在!')

    else

//-------------------2 使用FileOpen获取一个文件HANDLE--------//

        FFileHandle := FileOPen(fileName,fmOPenReadWrite);

    //如果创建文件失败，就抛出一个异常

    if FFileHandle = INVALID_HANDLE_VALUE then

        raise Exception.Create('打开或创建文件失败！');

//-------------------3 使用CreateFileMapping创建一个刚才用FileOpen创建的HANDLE的文件映射对象--



-//

    try

        FFileSize := GetFileSize(FFileHandle,nil);

        FMapHandle := CreateFileMapping(FFileHandle,nil,PAGE_READWRITE,0,FFileSize,nil);



        if FMapHandle = 0 then

            raise Exception.Create('创建内存映射文件失败！');

    finally

        CloseHandle(FFileHandle);

    end;

//-------------------4 使用MapViewOfFile创建一个CreateFileMapping建立的HANDLE的映射文件的视图到



进程的地址空间------//

    try

        FData := MapViewOfFile(FMapHandle,FILE_MAP_ALL_ACCESS,0,0,FFileSize);

        if FData = nil then

            raise Exception.Create('映射文件失败!');

    finally

        CloseHandle(FMapHandle);

    end;

//-------------------5 对MapViewOfFile返回的指针做相应的运算操作------//

    try

        PData := PChar(FData);

        inc(PData,FFileSize);

        PData^ := #0;



        if UCase then

            StrUpper(PChar(FData))

        else

            StrLower(PChar(FData));

    finally

//-------------------6 取消文件视图的映射------//

        UnmapViewOfFile(FData);

    end;

    txtContent.Lines.Clear();

    txtContent.Lines.LoadFromFile(fileName);

end;



procedure TForm1.btnCloseClick(Sender: TObject);

begin

    Form1.Close();

end;



end.



{

//-------------------------------------------------------//

在做指针具体运算时，可以采用这样直接获取该指针处的某一类型的值

procedure TForm1.Button1Click(Sender: TObject);

var i: Integer;

     p: Pointer;

begin

   i := 12345678;

   p := @i;

   showmessage(inttostr(integer(p)));   //俺的电脑上1242664,这是一个地址

   showmessage(inttostr(Pinteger(p)^));   //12345678

   showmessage(inttostr(PWord(p)^)); //24910

end;



Pinteger(p)^表示指针P处取得一个Integer值

PWord(p)^表示指针P处取得一个Word值

在windows.pas和system.pas中还定义了很多指针类型如下

  PInteger      = ^Integer;     {$NODEFINE PInteger}    { defined in sysmac.h }

  PCardinal     = ^Cardinal;

  PWord         = ^Word;

  PSmallInt     = ^SmallInt;    {$NODEFINE PSmallInt}   { defined in sysmac.h }

  {$POINTERMATH ON}

  PByte         = ^Byte;        {$NODEFINE PByte}       { defined in sysmac.h }

  {$POINTERMATH OFF}

  PShortInt     = ^ShortInt;    {$NODEFINE PShortInt}   { defined in sysmac.h }

  PInt64        = ^Int64;       {$NODEFINE PInt64}      { defined in sysmac.h }

  PUInt64       = ^UInt64;

  PLongWord     = ^LongWord;    {$NODEFINE PLongWord}   { defined in sysmac.h }

  PSingle       = ^Single;      {$NODEFINE PSingle}     { defined in sysmac.h }

  PDouble       = ^Double;      {$NODEFINE PDouble}     { defined in sysmac.h }

  PDate         = ^Doub

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