stream转string，string转stream

            FileStream fstPreview = 

                new FileStream(stPath, FileMode.Open, FileAccess.Read, FileShare.Read);

            StreamReader srdPreview = new StreamReader(ss);

            String temp = string.Empty;

            while (srdPreview.Peek() > -1)

            {

                String input = srdPreview.ReadLine();

                temp += input;

 

            }

            srdPreview.Close();

            return temp ;

Stream   s   =   new   MemoryStream(ASCIIEncoding.Default.GetBytes("Test   String"));