C++ 当涉及部分虚拟继承时，这是计算创建的基类对象数量的正确方法吗？

从我对虚拟继承的了解来看，每当我们有一个类a（基类），类B、C、D（这三个类实际上都继承类a），那么如果有一个类派生自类B，C和D类实例化后，将只创建类a的单个对象

我试图通过不同的案例来解释虚拟继承：

案例1:

0x7ffc8adac1c0
0x7ffc8adac1c0

0x7ffd512429c8
0x7ffd512429c8
0x7ffd512429bc

假设派生的类仅从类B和类C继承。即使这样，只有一个类a的对象被实例化，对吗

我试图用这段代码来验证这一点，但情况确实如此：

#include <iostream>
using namespace std;
class A
{
    public:
    int a;
};
class B: virtual public A
{
  public:
  int b;
};
class C: virtual public A
{
    public:
    int c;
};
class D: virtual public A
{
    public:
    int d;
};
class derived: public B, public C
{
    public:
    int y;
};
int main() 
{
    derived dObj;
    cout<<&(dObj.B::a)<<'\n';
    cout<<&(dObj.C::a)<<'\n';
    return 0;
}

#include <iostream>
using namespace std;
class A
{
    public:
    int a;
};
class B: virtual public A
{
  public:
  int b;
};
class C: virtual public A
{
    public:
    int c;
};
class D: public A
{
    public:
    int d;
};
class derived: public B, public C, public D
{
    public:
    int y;
};
int main() 
{
    derived dObj;
    cout<<&(dObj.B::a)<<'\n';
    cout<<&(dObj.C::a)<<'\n';
    cout<<&(dObj.D::a)<<'\n';
    return 0;
}

案例2:

0x7ffc8adac1c0
0x7ffc8adac1c0

0x7ffd512429c8
0x7ffd512429c8
0x7ffd512429bc

假设派生的类继承自类B、C和D，但类D实际上不继承类A。在本例中，类A的两个对象被实例化，对吗一个用于B，C和一个用于D

我试图用这段代码来验证这一点，但情况确实如此：

#include <iostream>
using namespace std;
class A
{
    public:
    int a;
};
class B: virtual public A
{
  public:
  int b;
};
class C: virtual public A
{
    public:
    int c;
};
class D: virtual public A
{
    public:
    int d;
};
class derived: public B, public C
{
    public:
    int y;
};
int main() 
{
    derived dObj;
    cout<<&(dObj.B::a)<<'\n';
    cout<<&(dObj.C::a)<<'\n';
    return 0;
}

#include <iostream>
using namespace std;
class A
{
    public:
    int a;
};
class B: virtual public A
{
  public:
  int b;
};
class C: virtual public A
{
    public:
    int c;
};
class D: public A
{
    public:
    int d;
};
class derived: public B, public C, public D
{
    public:
    int y;
};
int main() 
{
    derived dObj;
    cout<<&(dObj.B::a)<<'\n';
    cout<<&(dObj.C::a)<<'\n';
    cout<<&(dObj.D::a)<<'\n';
    return 0;
}

现在我的问题是：

---

我的观察正确吗？也就是说，让我们假设我们有n类继承类A，如果从中继承m（1来自cppreference网站中的内容，那么情况确实如此：

#include <iostream>
using namespace std;
class A
{
    public:
    int a;
};
class B: virtual public A
{
  public:
  int b;
};
class C: virtual public A
{
    public:
    int c;
};
class D: virtual public A
{
    public:
    int d;
};
class derived: public B, public C
{
    public:
    int y;
};
int main() 
{
    derived dObj;
    cout<<&(dObj.B::a)<<'\n';
    cout<<&(dObj.C::a)<<'\n';
    return 0;
}

#include <iostream>
using namespace std;
class A
{
    public:
    int a;
};
class B: virtual public A
{
  public:
  int b;
};
class C: virtual public A
{
    public:
    int c;
};
class D: public A
{
    public:
    int d;
};
class derived: public B, public C, public D
{
    public:
    int y;
};
int main() 
{
    derived dObj;
    cout<<&(dObj.B::a)<<'\n';
    cout<<&(dObj.C::a)<<'\n';
    cout<<&(dObj.D::a)<<'\n';
    return 0;
}