Constructor call sequence

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?

@LightnessRacesinOrbit They are related; being `virtual` does not change the situation. But I do consider the answer given in this Question more clear than in the other one. — MicroVirus, Jul 04 '14 at 15:50
Eduard, the `virtual` portion of the above question is irrelevant to the answer. Do you mind if we eliminate it from the question, so that this question is more universally applicable? — Yakk - Adam Nevraumont, Jul 04 '14 at 15:54

T.C. · Accepted Answer · 2014-07-25T01:29:25.337

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).

This answer is, in my opinion, much clearer than the flagged-for-duplicate answers. — MicroVirus, Jul 04 '14 at 15:39

Constructor call sequence

1 Answers1