Namespace Scope Question

I have a quick question about namespace scope:

1. I have two namespaces, A and B, where B is nested inside A.
2. I开发者_高级运维 declare some typedefs inside A.
3. I declare a class inside B ( which is inside A )

To access the typedefs (declared in A), from inside B, do I need to do "using namespace A;"

ie:

B.hpp:

using namespace A;

namespace A {
namespace B {

  class MyClass {

    typedeffed_int_from_A a;
  };

}
}

This seems redundant... Is this correct?

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To access the typedefs (declared in A), from inside B, do I need to do "using namespace A;"

No.

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However if there is a typedef or some other symbol with same name as your typedef, defined in the namespace B, then you need to write this:

A::some_type a;

Lets do a simple experiment to understand this.

Consider this code: (must read the comments)

namespace A
{
   typedef int some_type; //some_type is int

   namespace B
   {
        typedef char* some_type;  //here some_type is char*

        struct X
        {
               some_type     m; //what is the type of m? char* or int?
               A::some_type  n; //what is the type of n? char* or int?
        };

        void f(int) { cout << "f(int)" << endl; }
        void f(char*) { cout << "f(char*)" << endl; }
   }
}

int main() {
        A::B::X x;
        A::B::f(x.m);
        A::B::f(x.n);
        return 0;
}

Output:

f(char*)
f(int)

That proves that type of m is char* and type of n is int as expected or intended.

Online Demo : http://ideone.com/abXc8

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No, you don't need a using directive; as B is nested inside of A, the contents of A are in scope when inside B.