C++ global extern “C” friend can't reach private member on namespaced class

Question

Please consider the code:

#include    

using namespace std;

extern  \"C\"
void    foo( void );

namespace   A
{
    template< int No >
           


        

Answer 1

You need to declare the friend as extern "C". Your current friend declaration finds a friend foo in the global namespace that has C++ name mangling.