Question

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C++ namespace question

I have seen a couple of examples where there isnt a namespace. What is the advantage of that?

Answer 1

The ::fn refers to something in the global namespace (it is an absolute path). Note you can import stuff into the global namespace using the using <obj>; or using namespace <name>;

The namespace::fn refers to something in a namespace relative to the current namespace (it is a relativepath).

namespace X
{
     namespace Y
     {
           int Z()
           {
               N::fn();
               // Compiler looks for
               //      ::X::Y::N::fn()
               //      ::X::N::fn()
               //      ::N::fn()
               //
               // The search is done in that order the first found
               // is used. Note this is done at compile time only.


               ::fn(); // Absolute path. No search done.
                       // looks for `fn()` in the global namespace

               fn();   // Relative path no namespace
                       // Searchs for ::X::Y::fn()
                       //             ::X::fn()
                       //             ::fn()



               ::X::fn(); // Absolute path no search done.
                          // looks for `fn()` in the namespace X which must be
                          // in the global namespace.
           }
     }          
 }