搜索字符串在流中的位置

(*//
標題:搜索字符串在流中的位置
說明:適用於文件搜索等
設計:Zswang
支持:[email protected]
日期:2004-03-21
//*)

(*//============================================================================
設計思路:
從流中將數據取到緩沖中
再逐一對緩沖進行搜索
============================================================================//*)

function ScanStream(mStream: TStream; mStr: string): Integer;
const
  cBufferSize = $8000;
var
  S: string;
  T: string;
  I: Integer;
  L: Integer;
begin
  Result := -1;
  if not Assigned(mStream) then Exit;
  if mStr = '' then Exit;
  L := Length(mStr);
  mStream.Position := 0;
  SetLength(S, cBufferSize);
  T := '';
  for I := 1 to mStream.Size div cBufferSize do begin
    mStream.Read(S[1], cBufferSize);
    Result := Pos(mStr, T + S) - 1; //保留上次搜索的尾部字符～～
    T := Copy(S, cBufferSize - L, MaxInt);
    if Result >= 0 then begin
      Result := Result + Pred(I) * cBufferSize - Length(T);
      Exit;
    end;
  end;
  I := mStream.Size mod cBufferSize;
  SetLength(S, I);
  if I > 0 then begin
    mStream.Read(S[1], I);
    Result := Pos(mStr, T + S) - 1;
    if Result >= 0 then begin
      Result := Result + mStream.Size - I - Length(T);
      Exit;
    end;
  end;
end; { ScanStream }

//Example
procedure TForm1.Button1Click(Sender: TObject);
var
  vFileStream: TFileStream;
begin
  vFileStream := TFileStream.Create('C:	emp	emp.exe', fmShareDenyNone);
  try
    Label1.Caption := IntToStr(ScanStream(vFileStream, Edit1.Text));
  finally
    vFileStream.Free;
  end;
end;