Namespace

Namespaces act as a scope/grouping around declarations (named types, variables, functions, etc.) to prevent name collisions and help organise code.

To create a namespace:

namespace GroupA {
  int var = 1;
  void foo() {}
}

Then access the members of the namespace with the scope operator (::):

GroupA::var;
GroupA::foo();

Namespaces can be nested:

namespace GroupA {
  namespace GroupB {
    int bar = 2;
  }
}

GroupA::GroupB::bar;

You can bring the members of a namespace into global scope with the using directive:

using namespace GroupA;

Which lets you access those members without the scope operator:

var;
foo();

Nested namespaces can be defined with the shorthand :: syntax:

namespace GroupC::GroupD {
  int car = 3;
}

GroupC::GroupD::car;