Thank you! (string)C works with the downloaded chain.
How do you recommend to reset PUT/CALL flags?
Why is preferable to setting Expiry to 0?
I then thought of sorting the Contracts list and cutting the unnecessary lines altogether by setting NumContracts to a smaller value..Is this at all possible?

Is the class just typecasted to/from double? I.e. a dataset will need to have the first column saved as e.g.(double)Class (where Class is a string)?
And when such Contract* C is passed to contractPrice(C) it is automatically assumed to contain class in its first field?