An example about namespace in C++

Question

namespace A::B {
  class MyClass{};
}

Can anyone tell me why this code does not compile?

Answer 1

Your code uses nested namespaces, which are a C++17 feature. You probably get an error because your compiler doesn't support C++17, or you haven't configured it to understand C++17. The pre-C++17 version of your code would be

namespace A {
namespace B {
    class MyClass {};
}
}