Hello everyone,
Here is the related C++ Spec and my test code. I think virtual base class, no matter direct virtual base class or not, will always be constructed before non-virtual class (including non-virtual direct base class), correct?
Another question is, what means "and only for the constructor of the most derived class as described below" in related Spec statements?
Spec:
--------------------
12.6.2 Initializing bases and members [class.base.init]
5 Initialization shall proceed in the following order:
— First, and only for the constructor of the most derived class as described below, virtual base classes shall
be 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 class names in the derived
class base-specifier-list.
— Then, direct base classes shall be initialized in declaration order as they appear in the base-specifier-list
(regardless of the order of the mem-initializers).
— Then, nonstatic data members shall be initialized in the order they were declared in the class definition
(again regardless of the order of the mem-initializers).
— Finally, the body of the constructor is executed.
[Note: the declaration order is mandated to ensure that base and member subobjects are destroyed in the
reverse order of initialization. ]
--------------------
Code:/*
output
constructor B1
constructor B2
constructor D2
constructor D1
constructor D3
*/
#include <iostream>
using namespace std;
class B1 {
public:
B1()
{
cout << "constructor B1 " << endl;
}
};
class B2 {
public:
B2()
{
cout << "constructor B2 " << endl;
}
};
class D1 : virtual public B1 {
public:
D1()
{
cout << "constructor D1 " << endl;
}
};
class D2 : public virtual B1, public B2 {
public:
D2()
{
cout << "constructor D2 " << endl;
}
};
class D3 : public D1, virtual public D2 {
public:
D3()
{
cout << "constructor D3 " << endl;
}
};
int main()
{
D3 d;
return 0;
}
thanks in advance,
George
