القراءة من ملف ثنائى عند عنوان محدد

كود :
unit search;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function ScanFile(const FileName: string;
  const forString: string;
  caseSensitive: Boolean): Longint;
const
  BufferSize = $8001;  { 32K+1 bytes }
var
  pBuf, pEnd, pScan, pPos: PChar;
  filesize: LongInt;
  bytesRemaining: LongInt;
  bytesToRead: Integer;
  F: file;
  SearchFor: PChar;
  oldMode: Word;
begin
  { assume failure }
  Result := -1;
  if (Length(forString) = 0) or (Length(FileName) = 0) then Exit;
  SearchFor := nil;
  pBuf      := nil;
  { open file as binary, 1 byte recordsize }
  AssignFile(F, FileName);
  oldMode  := FileMode;
  FileMode := 0;    { read-only access }
  Reset(F, 1);
  FileMode := oldMode;
  try { allocate memory for buffer and pchar search string }
    SearchFor := StrAlloc(Length(forString) + 1);
    StrPCopy(SearchFor, forString);
    if not caseSensitive then  { convert to upper case }
      AnsiUpper(SearchFor);
    GetMem(pBuf, BufferSize);
    filesize       := System.Filesize(F);
    bytesRemaining := filesize;
    pPos           := nil;
    while bytesRemaining > 0 do
    begin
      { calc how many bytes to read this round }
      if bytesRemaining >= BufferSize then
        bytesToRead := Pred(BufferSize)
      else
        bytesToRead := bytesRemaining;
      { read a buffer full and zero-terminate the buffer }
      BlockRead(F, pBuf^, bytesToRead, bytesToRead);
      pEnd  := @pBuf[bytesToRead];
      pEnd^ := #0;
      pScan := pBuf;
      while pScan < pEnd do
      begin
        if not caseSensitive then { convert to upper case }
          AnsiUpper(pScan);
        pPos := StrPos(pScan, SearchFor);  { search for substring }
        if pPos <> nil then
        begin { Found it! }
          Result := FileSize - bytesRemaining +
            Longint(pPos) - Longint(pBuf);
          Break;
        end;
        pScan := StrEnd(pScan);
        Inc(pScan);
      end;
      if pPos <> nil then Break;
      bytesRemaining := bytesRemaining - bytesToRead;
      if bytesRemaining > 0 then
      begin
        Seek(F, FilePos(F) - Length(forString));
        bytesRemaining := bytesRemaining + Length(forString);
      end;
    end; { While }
  finally
    CloseFile(F);
    if SearchFor <> nil then StrDispose(SearchFor);
    if pBuf <> nil then FreeMem(pBuf, BufferSize);
  end;
end; { ScanFile }

procedure TForm1.Button1Click(Sender: TObject);
var
  openDialog : TOpenDialog;
     Position: integer;
begin
      openDialog := TOpenDialog.Create(self);
 openDialog.InitialDir := 'c:\';
         openDialog.Options := [ofFileMustExist];
       openDialog.Filter :=
    'EXE FILE|*.EXE|ANY FILE|*.*';
    openDialog.FilterIndex := 2;
  if openDialog.Execute
  then ShowMessage(openDialog.FileName)
  else ShowMessage('Open file was cancelled');
      Position := ScanFile(openDialog.FileName, edit1.text, False);
  edit2.Text:=(IntToStr(Position));
    openDialog.Free;
    
    end;

end.