Optional function parameters: Use default arguments (NULL) or overload the function?

Question

I have a function that processes a given vector, but may also create such a vector itself if it is not given.

I see two design choices for such a case, where a func

Answer 1

The first way is poorer because you cannot tell if you accidentally passed in NULL or if it was done on purpose... if it was an accident then you have likely caused a bug.

With the second one you can test (assert, whatever) for NULL and handle it appropriately.