I ran into some problems in using virtual base class.
Helps are appreciated.  SGI C++ 3.0.1 gives fatal error
when I cast the pointer of a derived class to a pointer
of its virtual base class.  What does ANSI C++ say about
this?

For example, the following does not compile.  Is this a
problem of this specific compiler?

--------------
class base {};

class deriveL1A : virtual public base {};
class deriveL1B : virtual public base {};
class deriveL2 : public deriveL1A, public deriveL1B {};


int main() {
    deriveL1A d;
    base* b = &d;

    deriveL1A* c = (deriveL1A*) b;
}

--------------

Thanks in advance.