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

In C++ you should avoid allowing valid NULL parameters whenever possible. The reason is that it substantially reduces callsite documentation. I know this sounds extreme but I work with APIs that take upwards of 10-20 parameters, half of which can validly be NULL. The resulting code is almost unreadable

SomeFunction(NULL, pName, NULL, pDestination);

If you were to switch it to force const references the code is simply forced to be more readable.

SomeFunction(
  Location::Hidden(),
  pName,
  SomeOtherValue::Empty(),
  pDestination);