C ++ virtual base class

When a base class is declared as a virtual base class, even if it becomes a public base class on multiple inheritance links, the final derived class only has one backup of it. For example:
Class cbase {};
Class cderive1: virtual public cbase {};
Class cderive2: virtual public cbase {};
Class cderive12: Public cderive1, cderive2 {};
Only one object data class cbase is available in the cderive12 object.

Features of the virtual base class:

The parameters of the virtual base class constructor must be initialized by the newly derived class (even if it is not directly inherited );
The constructor of the virtual base class is executed before the constructor of the non-virtual base class.