流怎么理解

Question

标红的地方怎么理解：//用流压缩文件  
procedure CompressStream(var MyStream: TMemoryStream);
  var
      SourceStream: TCompressionStream;
      DestStream: TMemoryStream;
      Count: Integer;
  Begin   
      Count:= MyStream.Size;
      DestStream:= TMemoryStream.Create;
      SourceStream:=TCompressionStream.Create(clDefault, DestStream);   
      Try   
          MyStream.SaveToStream(SourceStream);
          SourceStream.Free;   
          MYStream.Clear;   
          MyStream.WriteBuffer(Count, SizeOf(Count)); //这个怎么理解，
          MyStream.CopyFrom(DestStream, 0);
          MyStream.Position:= 0;   
      finally
          DestStream.Free;
      end;
  end;
//解压
  procedure   UnCompressStream(var   MyStream:   TMemoryStream);
  var
      SourceStream:   TDecompressionStream;
      Buffer:   PChar;
      Count:   Integer;
  Begin
      //这个怎么理解，Count是整型的，整型的SizeOf()也就是四字节罢了
      MyStream.ReadBuffer(Count, SizeOf(Count));
      GetMem(Buffer, Count);
      SourceStream:= TDecompressionStream.Create(MyStream); //好像没有释放？
      Try
          SourceStream.ReadBuffer(Buffer^, Count);
          MyStream.Clear;
          MyStream.WriteBuffer(Buffer^, Count);
          MyStream.Position:= 0;
      finally
          FreeMem(Buffer);
      end;
  end;

Answer 1

MyStream.WriteBuffer(Count, SizeOf(Count)); //这句话是将count写入流,长度4字节,执行完后,你查看MyStream.size就知道了
MyStream.ReadBuffer(Count, SizeOf(Count));  //这句是读出数据到count,与上面反之

Answer 2

MyStream.WriteBuffer(Count, SizeOf(Count)); //将Count值写到MyStream的当前位置
MyStream.ReadBuffer(Count, SizeOf(Count)); //取出MyStream当前位置的4个字节数据，并放入Count中

Answer 3

TCompressionStream和TDecompressionStream，是不是不用释放呀？

Answer 4

procedure CompressStream(var MyStream: TMemoryStream); 
  var 
      SourceStream: TCompressionStream; 
      DestStream: TMemoryStream; 
      Count: Integer; 
  Begin  
      Count:= MyStream.Size; 
      DestStream:= TMemoryStream.Create; 
      SourceStream:=TCompressionStream.Create(clDefault, DestStream);  
      Try  
          MyStream.SaveToStream(SourceStream); 
          SourceStream.Free;  
          MYStream.Clear;  
          MyStream.WriteBuffer(Count, SizeOf(Count)); //将Count值写到MyStream的当前位置  
          MyStream.CopyFrom(DestStream, 0); 
          MyStream.Position:= 0;  
      finally 
          DestStream.Free; 
      end; 
  end; 
//解压 
  procedure  UnCompressStream(var  MyStream:  TMemoryStream); 
  var 
      SourceStream:  TDecompressionStream; 
      Buffer:  PChar; 
      Count:  Integer; 
  Begin 
      MyStream.ReadBuffer(Count, SizeOf(Count)); {取出MyStream当前位置的4个字节数据，并放入Count中}
      GetMem(Buffer, Count); 
      SourceStream:= TDecompressionStream.Create(MyStream); //在下面Free下就O了 
      Try 
          SourceStream.ReadBuffer(Buffer^, Count); 
          MyStream.Clear; 
          MyStream.WriteBuffer(Buffer^, Count); 
          MyStream.Position:= 0; 
          SourceStream.Free
      finally 
          FreeMem(Buffer); 
      end; 
  end;