To me, this seems similar to asking what should int divide(int numerator, int denominator) do when denominator == 0, or what should a modern version of i

To me, this seems similar to asking what should int divide(int numerator, int denominator) do when denominator == 0, or what should a modern version of int atoi(const char* s) do when s == "foo"? I.e., the answer is that the parameter lies outside the domain of well-supported values, so ideally the callee should somehow help the programmer realize they have a programming error.