18.29.txt

Exercise 18.29: Given the following class hierarchy:

	class Class { ... };
	class Base : public Class { ... };
	class D1 : virtual public Base { ... };
	class D2 : virtual public Base { ... };
	class MI : public D1, public D2 { ... };
	class Final : public MI, public Class { ... };

	(a) In what order are constructors and destructors run on a Final object?
	(b) A Final object has how many Base parts? How many Class parts?
	(c) Which of the following assignments is a compile-time error?
		Base *pb;	Class *pc;	MI *pmi;	D2 *pd2;
		(a) pb = new Class;		(b) pc = new Final;
		(c) pmi = pb;			(d) pd2 = pmi;

By Faisal Saadatmand

(a)
	Class();		// run by Base default constructor
	Base();			// D1 & D2 virtual base class initialized first
	D1();			// indirect nonvirtual base class
	D2();			// indirect nonvirtual base class
	MI();			// first direct nonvirtual base class
	Class();		// second direct nonvirtual base class (initialized again)
	Final();		// most derived class

Note: virtual base classes are initialized first.(p. 814) In this case, Base is a
virtual base class. However, since Base is derived directly from
Class, its default constructor will run Class() before it does its work.

(b) 1 Base subparts and 2 Class subparts.

(c)
	(a) Error: invalid base-to-derived type conversion
	(b) Error: Class is inaccessible directly due to ambiguity (p. 812-813)
	(c) Error: invalid base-to-derived type conversion
	(d) valid, but pmi is uninitialized