Is it a good idea to use varargs in a C API to set key value pairs?

Question

I am writing an API that updates a LOT of different fields in a structure.

I could help the addition of future fields by making the update function variadic:

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Answer 1

I'd take a long hard look at any "update" functionality designed to be used externally (or even internally) which uses the same function to update many different fields in a structure. Is there a specific reason why you can't have discrete functionality for updating the fields?