[cfe-dev] Why this extern "C" fails ?

[David Chisnall]

On 30 Jul 2013, at 06:43, Arji Cot <arjicot at gmail.com> wrote:

> 1 ) this works flawlessly, and as far as I know C and C++ have the same rules for scoping
> 
> #include <iostream>
> 
> int main() {
>   {
>     int a = 42;
>     { std::cout << a << "\n"; }
>   }
>   return (0);
> }

This does not have the same scoping as this:

> #include <iostream>
> 
> int main() {
>   {
>     extern "C" { int a = 42; }
>     { std::cout << a << "\n"; } 
>   }
>   return (0);
> }

The equivalent is:

#include <iostream>

int main() {
  {
    { int a = 42; }
    { std::cout << a << "\n"; }
  }
  return (0);
}

The scope of a is the block in which it is declared, so it is not in scope by the time it is used.

Perhaps your original example was meant to be:

#include <iostream>

int main() {
  {
    extern "C" int a = 42;
    { std::cout << a << "\n"; }
  }
  return (0);
}

This also fails to compile.  I'm not sure what you'd expect the semantics to be.  The variable a has automatic storage, and so a linkage specifier makes no sense in this context.  

David