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

One problem with varargs in C is that you don't know how many arguments are passed, so you need that as another parameter:

update(2, FIELD_NAME1, 10, FIELD_NAME2, 20);

update(3, FIELD_NAME1, 10, FIELD_NAME2, 20, FIELD_NAME3, 30);