Your example is wrong. This function is compatible with C++ as soon as you document it as not accepting exception-throwing callbacks.
The most general definition of the restriction is that C++ code cannot throw exceptions through exception unsafe code. How do you know if your C++ function was called from exception unsafe code? You can't!
So it's only ever safe to throw an exception when you are expecting it to be caught immediately i.e. you can use exceptions as glorified error codes, but not much else.
In Django I can throw a Http404 exception from deep inside a view and the server will come up with a 404 response. I can assert and the client will get a 500 error but the server won't go down. This is the real power of exceptions, and God help anybody who tries to do it in C++.
In the enterprise context you can hardly count on proper documentation, specially in projects with high attrition of consultants where each one comes, implements something and departures to the next gig.
Not to count the commercial libraries distributed in binary only form.
So one never knows if the code is exception safe, don't work with exceptions or is exception happy.