C++ namespaces are a way to avoid library A's symbol "cow" clashing with library B's symbol "cow" without everything being named library_a_cow and library_b_cow all over the place which is annoying. I agree C would be nicer with such a namespace feature.
However this technique is about what happens when you realise your structure members x and y should be inside a sub-structure position, and you want both:
d = calculate_distance(s.x, s.y); // Old code
and
d = calculate_distance(s.position.x, s.position.y); // New
... to work while you transition to this naming.
