Virtual inheritance not behaving like I expected

[seven50]

Hi, I'm writing some code to test how virtual inheritance behaves, my problem is that the virtual inheritance behaves like a "normal" public inheritance

non virtual inheritance - http://ideone.com/2joewK
virtual inheritance - http://ideone.com/WXTo2Z

as you can see the output is 1:1 the same, how is this possible ?

In my understanding virtual inheritance can be used to guide the construction of an object according to the inheritance itself, meaning that I'm surprised to see the call to the ctor and dtor of A when using virtual inheritance in the second example.

What I'm doing wrong and what are the practical aspect of virtual inheritance ?

I'm posting the same examples here

ctor_NON_virtual_inheritance.cpp

#include <iostream>

class A
{
    std::string k;
    int j;
  public:
    A() { std::cout << "ctor A" << std::endl;};
    ~A() { std::cout << "dtor A" << std::endl;};
};

class B : public A
{
  public:
    B() { std::cout << "ctor B" << std::endl;};
    ~B() {std::cout << "dtor B" << std::endl;};
};

int main()
{
  {
    std::cout << "building an A obj" << std::endl;
    A a;
  }
  {
    std::cout << "building a  B obj" << std::endl;
    B b;
  }
  return(0);
}

ctor_virtual_inheritance.cpp

#include <iostream>

class A
{
    std::string k;
    int j;
  public:
    A() { std::cout << "ctor A" << std::endl;};
    ~A() { std::cout << "dtor A" << std::endl;};
};

class B : public virtual A
{
  public:
    B() { std::cout << "ctor B" << std::endl;};
    ~B() {std::cout << "dtor B" << std::endl;};
};

int main()
{
  {
    std::cout << "building an A obj" << std::endl;
    A a;
  }
  {
    std::cout << "building a  B obj" << std::endl;
    B b;
  }
  return(0);
}

Thanks.

[cire]

In my understanding virtual inheritance can be used to guide the construction of an object according to the inheritance itself, meaning that I'm surprised to see the call to the ctor and dtor of A when using virtual inheritance in the second example.

What I'm doing wrong and what are the practical aspect of virtual inheritance ?

You aren't doing anything wrong. That you're surprised seems to suggest you don't have any idea what virtual inheritance is. Googling and following the top link or two should sort that out for you.

[seven50]

I'm not getting the practical aspects of this, can you point me to an article with real code and an exhaustive explanation about this kind of inheritance ?

[kevinkjt2000]

Here is what cire suggested:
https://www.google.com/#sclient=psy-ab&q=virtual+class+inheritance

I saw:
http://en.wikipedia.org/wiki/Virtual_inheritance
http://www.cprogramming.com/tutorial/virtual_inheritance.html
http://stackoverflow.com/questions/419943/virtual-inheritance
http://msdn.microsoft.com/en-us/library/wcz57btd(v=vs.80).aspx
http://www.deitel.com/articles/cplusplus_tutorials/20060225/virtualBaseClass/

[seven50]

thanks, I'm experimenting with and I think that now I get how this and a dynamic typed language behave at runtime.