anonymous namespace

Question

What is the different between these two?

cpp-file:

namespace
{
    int var;
}

or

int var;

if both

Answer 1

In your second case, when you don't use an anonymous namespace, if any other cpp file declares an extern int var;, it will be able to use your variable.

If you use an anonymous namespace, then at link time, the other cpp file will generate an undefined reference error.