c++ Proper position for 'using namespace'

Question

I was integrating some C++ in somelse's one and found out we adopt two different strategies regarding the use of using namespace commands.

For cleanliness of source code, which of the two is the most correct solution?

namespace foo
{
   using namespace bar;
}

or

using namespace bar;

namespace foo
{
}

Thanks a lot for your help,

T.

Answer 1

The two are not equivalent. In the first case the namespace bar is imported in the namespace foo so for every bar::x you can access it as foo::x. In the latter the namespace bar is imported in the global namespace (or the namespace that wraps both up) and it can be accessed as ::x.

I'd recommend to always choose the narrowest possible solution for you. Even to the point of including the namespace only in the function you actually need it. So if you are in doubt go with the first one.