Where is the “virtual” keyword necessary in a complex multiple inheritance hierarchy?

Question

I understand the basics of C++ virtual inheritance. However, I\'m confused about where exactly I need to use the virtual keyword with a complex class hierarchy. F

Answer 1

You have to specify virtual inheritance when inheriting from any of A, B, C, and E classes (that are at the top of a diamond).

class A;
class B: virtual A;
class C: virtual A;
class D: virtual B;
class E: virtual B, virtual C;
class F: virtual C;
class G:         D, virtual E;
class H: virtual E,         F;
class I:         G,         H;