The way C3[0] handles this is fairly interesting. An function returning an optional in C3, such as:

    fn int? run_operation_by_id(int id);

Would be equivalent to the following in C:

   /* ABI type definitions omitted for brevity */
   c3fault_t run_operation_by_id(int *return_value, int id);

[0] https://c3-lang.org