计算机二级Delphi辅导:文件/流的加密解密方法
来源:优易学  2011-6-5 16:59:22   【优易学:中国教育考试门户网】   资料下载   IT书店

 

  i := InStream.Size mod BufSize;
  if (i > 0) then begin
  InStream.ReadBuffer(Buf, i);
  ComStream.Write(Buf, i);
  End;
  InStream.Free;
  InStream := nil;
  ComStream.Free;
  ComStream := nil;
  // 在此写加密流代码(要先释放 ComStream), Postion = 0
  // EncryptStream(Stream);
  except
  on E: Exception do begin
  if (InStream <> nil) then
  InStream.Free;
  if (ComStream <> nil) then
   ComStream.Free;
  MessageDlg(COMPRESS_ERROR + #10 + E.Message, mtError, [mbOk], 0);
  end;
  end;
  end;
  // 解压文件到流
  procedure DecompressToStream(FileName: String; Stream: TStream);
  var
  i: Integer;
  Buf: array[0..BufSize] of Byte;
  DecomStream: TDecompressionStream;
  MemStream: TMemoryStream;
  begin
  if not FileExists(FileName) then
  Exit;
  MemStream := Nil;
  DecomStream := nil;
  try
  // 生成流
  // 先读文件到 MemStream 中解密(FileName 只读).
  // DecomStream 的开始位置 = MemStream.Position
  MemStream := TMemoryStream.Create;
  MemStream.LoadFromFile(FileName);
  // 在此写解密流代码
  // DecryptStream(MemStream);
  DecomStream := TDeCompressionStream.Create(MemStream);
  // 解压流, Postion = 0
  repeat
  i := DecomStream.Read(Buf, BufSize);
  Stream.WriteBuffer(Buf, i);
  until (i = 0);
  Stream.Position := 0;
  DecomStream.Free;
  DecomStream := nil;
  MemStream.Free;
  MemStream := Nil;
  except
  on E: Exception do begin
  if (MemStream <> nil) then
  MemStream.Free;
  if (DecomStream <> nil) then
  DecomStream.Free;
  MessageDlg(DECOMPRESS_ERROR + #10 + E.Message, mtError, [mbOk], 0);
  end;
  end;
  end;
  // 压缩流
  procedure CompressStream(InStream, OutStream: TStream);
  var
  i: Integer;
  Buf: array[0..BufSize] of byte;
  ComStream: TCompressionStream;
  begin
  ComStream := Nil;
  try
  InStream.Position := 0;
  ComStream := TCompressionStream.Create(clMax, OutStream);
  for i := 1 to (InStream.Size div BufSize) do begin
  InStream.ReadBuffer(Buf, BufSize);
  ComStream.Write(Buf, BufSize);
  end;

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