Question

In visual C++, I can do things like this:

template <class T> class A{ protected:     T i; };  template <class T> class B : public A<T>{     T geti() {return i;} }; 

If I try to compile this in g++, I get an error. I have to do this:

template <class T> class B : public A<T>{     T geti() {return A<T>::i;} }; 

Am I not supposed to do the former in standard C++? Or is something misconfigured with gcc that’s giving me errors?

Answer 1

This used to be allowed, but changed in gcc 3.4.

In a template definition, unqualified names will no longer find members of a dependent base (as specified by [temp.dep]/3 in the C++ standard). For example,

    template <typename T> struct B {       int m;       int n;       int f ();       int g ();     };     int n;     int g ();     template <typename T> struct C : B<T> {       void h ()       {         m = 0; // error         f ();  // error         n = 0; // ::n is modified         g ();  // ::g is called       }     }; 

You must make the names dependent, e.g. by prefixing them with this->. Here is the corrected definition of C::h,

    template <typename T> void C<T>::h ()     {       this->m = 0;       this->f ();       this->n = 0       this->g ();     }