Question

i.e. if I define operators == and + in my class in a private section, can they be accessible from main?

It works in MSVS 2008 and 2010 but for me it seems to be a bug in a compiler. Is it so?

Answer 1

You will have to show the code to get a sensible explanation of why the compiler is accepting it. My guess is that you are implementing them as friend free functions. At any rate, for the sake of argument, assume you have:

class bar {
   friend bool operator==( bar const &, bar const & ) {
      return true;
   }
   bar operator+( bar const & ) {
      return *this;
   }
};

int main() {
   bar a, b;
   a == b;    // ok
   //a + b;   // nok: operator+ is private from this context
}

And now the explanation. In the example, operator+ is declared as a member function inside a private section, as such, access specifiers apply and unless main is a friend of the class it will not have access to it. On the other hand operator== is implemented as a free function (even if the definition is provided inside the class braces) and access specifiers do not apply there.

The code is almost equivalent (there is a small difference when it comes to lookup) to:

class bar {
   friend bool operator==( bar const &, bar const & ); // just declare as friend
   //...
};
bool operator==( bar const &, bar const & ) {
   return true;
}

Where it is much simpler to reason about accessibility of operator== from the main function.