Derived classes
cppreference Derived classes
Any class type (whether declared with class-key class or struct) may be declared as derived from one or more base classes which, in turn, may be derived from their own base classes, forming an inheritance hierarchy.
NOTE: C++ 支持multiple inheritance，这就使得它的inheritance hierarchy不是tree shape，而可能出现diamond problem
Each direct and indirect base class is present, as base class subobject, within the object representation of the derived class at implementation-defined offset. Empty base classes usually do not increase the size of the derived object due to empty base optimization. The constructors of base class subobjects are called by the constructor of the derived class: arguments may be provided to those constructors in the member initializer list.
NOTE: 上面这段话是对object layout的讨论，关于object layout，在下面章节中进行了讨论：
C++\Language-reference\Basic-concept\Data-model\Object
Virtual base classes
NOTE: 这部分内容放到了
Multiple-inheritance.md中。