Question

$10.2/4- “[ Note: Looking up a name in
an elaborated-type-specifier (3.4.4)
or base-specifier (Clause 10), for
instance, ignores all nontype
declarations, while looking up a name
in a nested-name-specifier (3.4.3)
ignores function, variable, and
enumerator declarations.”

I have found this statement to be very confusing in this section while describing about name lookup.

void S(){}

struct S{
   S(){cout << 1;}
   void f(){}
   static const int x = 0;
}; 

int main(){ 
   struct S *p = new struct ::S;  // here ::S refers to type
   p->::S::f();

   S::x;  // base specifier, ignores the function declaration 'S'

   ::S(); // nested name specifier, ignores the struct declaration 'S'.
   delete p;
} 

My questions:

1. Is my understanding of the rules correct?

2. Why ::S on the line doing new treated automatically to mean struct S, whereas in the last line ::S means the functions S in the global namespace.

3. Does this point to an ambiguity in the documentation, or is it yet another day for me to stay away from C++ Standard document?

Answer 1

Q1: I think so.

Q2: Compatibility with C. When you declare a struct in C, the tag name is just that, a tag name. To be able to use it in a standalone way, you need a typedef. In C++ you don’t need the typedef, that makes live easier. But C++ rules have been complicated by the need to be able to import already existing C headers which “overloaded” the tag name with a function name. The canonical example of that is the Unix stat() function which uses a struct stat* as argument.

Q3: Standard reading is usually quite difficult… you need to already know that there is no place elsewhere modifying what you are reading. It isn’t strange that people knowing how to do that are language lawyer…