Virtual Inheritance

Virtual inheritance is actually quite simple as it dictates that identical base classes are to be merged into a single occurrence. For instance, given this:

class BaseA
{
public:
    int a;
};

class BaseB: public BaseA
{
public:
    int b;
};

class BaseC: public BaseA
{
public:
    int c;
};

class Derived:
    public virtual BaseB,
    public virtual BaseC
{
    int d;
};

Derived will only contain a single instance of BaseA even if its inheritance graph dictates that it should have two

instances. The result looks something like this:

class Derived
{
public:
    int a;
    int b;
    int c;
    int d;
};

So the second instance of a is silently ignored because it would cause multiple instances of BaseA to exist in Derived,

which clearly would cause lots of confusion and ambiguities.