Creating a C++ namespace in header and source (cpp)

Question

Is there any difference between wrapping both header and cpp file contents in a namespace or wrapping just the header contents and then doing using namespace

Answer 1

There's no performance penalties, since the resulting could would be the same, but putting your Foo into namespace implicitly introduces ambiguity in case you have Foos in different namespaces. You can get your code fubar, indeed. I'd recommend avoiding using using for this purpose.

And you have a stray { after using namespace ;-)