C++ virtual inheritance /c++ dziedziczenie virtualne

:)
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#include <iostream>
using namespace std;
class A
{
public:
     void read()
    {
    cout << "This is A" << endl;
    }
private:

};
class B:virtual public A
{
public:

private:

};
class C:virtual public A
{
public:

private:

};
class D:public B,public C
{

};
int main()
{

D o1;
o1.read();
return 0;
}