Thank you so much for your great reply. It helped me a lot. I could solve my problem in a good way. Like you recommended I built a class around the file handle. In this helper class I also put the endianness and checksum computation. It works fine and is good encapsulated.
Also before beginning the coding I took a big piece of paper and was drawing all classes and interactions (inheritance/aggregation) between them. And then I could implement my task without the need to change something afterwards. A good design at the beginning helps a lot :-)