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;
    }
}

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

GroupA::GroupB::bar;
GroupC::GroupD::car;

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();

References

• cppreference: namespaces