anonymous namespace

Question

What is the different between these two?

cpp-file:

namespace
{
    int var;
}

or

int var;

if both

Answer 1

The second version is defined in the global namespace -- other .cpp files can get to it by declaring

extern int var;

and even if they don't do that, if someone else uses the same name in the global name space, you'll get a link error (multiply defined symbol).