Constructor call sequence [duplicate]

Question

Consider the following code:

class A {};

class B : virtual public A {};

class C : virtual public A {};

class D : public B, public C {};

D d;

The Visual Studio's compiler first calls the constructor of class B, then the constructor of class C. But is this a Rule, i.e. does the ISO C++ standard guarantee the order of constructor call?

Answer 1

It's guaranteed. From §12.6.2 [class.base.init]/p11 of N3797:

In a non-delegating constructor, initialization proceeds in the following order:

• First, and only for the constructor of the most derived class (1.8), virtual base classes are initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where “left-to-right” is the order of appearance of the base classes in the derived class base-specifier-list.
• Then, direct base classes are initialized in declaration order as they appear in the base-specifier-list (regardless of the order of the mem-initializers).
• Then, non-static data members are initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).