Void Pointer Arithmetic

Is there a better way than casting to a char pointer?

No (except having a char * instead of a void * to begin with, so you don't have to cast it at all).

If this is not desirable or possible, then the only way is:

ptr = static_cast<char *>(ptr) + offset;

(Note: if you are doing this sort of stuff in C++, usually there is a much better solution. Unless you are an expert and you already ruled out every other alternative, I suggest you post a new question asking if there is a better way to do what you're trying to do!)

Take a look at this question, and this question. To summarise, the answer is to cast to char * for arithmetic at a byte level.