Chapter 9 Class Inheritance and Virtual Functions

第 9 章基本 C++ 程式碼整理如下

Reference: I Horton, Ivor Horton's Beginning Visual C++ 2013 (Wiley 2014).

9.1 Object-Oriented Programming Basics

9.2 Inheritance in Classes
∎ Deriving classes form a base class
Ex9_01.cpp (main function; #include "CandyBox.h")
CandyBox.h (derived class; #include "Box.h"; class CCandyBox : CBox)
Box.h (base class; class CBox)


9.3 Access Control under Inheritance
∎ Accessing private members of the base classclass
CCandyBox : public CBox vs. CBox (or private CBox)

∎ The function members defined in the derived class cannot access the private date members of a base class. To access the private members of the base class, one has to move the function "double volume() const" from the derived class to the base class.

∎ Constructor operation in a derived class
CCandyBox(double lv, double wv, double hv, const char* str = "Candy") : CBox {lv, wv, hv}  // 1
explicit CCandyBox(const char* str = "Candy")  // 2

∎ The access level of inherited class member

9.4 The Copy Constructor in a Derived Class
∎ The copy constructor in a derived class (Ex9_05)
CCandyBox(const CCandyBox& initCB) vs. CCandyBox(const CCandyBox& initCB) : CBox{initCB}  // All copy constructors in both header files have to be called


9.5 Preventing Class Derivation
∎ Modifier "final"

9.6 Class Members as Friends


9.7 Virtual Functions
∎ Using an inherited function: early binding (Ex9_06)
myBox.showVolume();           // Call the volume() function in Box.h
myGlassBox.showVolume();  // Still call the volume() function in Box.h, not the one in GlassBox.h 

∎ Fixing the CGlassBox: late binding (Ex9_07)
virtual double volume() const  // Box.h
virtual double volume() const  // GlassBox.h; don't forget to specify volume() as const, otherwise you won't override the base function

∎ Ensuring correct virtual function operation (Modifier "override")
virtual double volume() const override  // The keyword "const" still cannot be omitted, however

∎ Preventing function overriding (Modifier "final)
virtual double volume() const final        // If you don't want this volume() function to be overridden

∎ Points to base and derived classes (Ex9_08)
CBox myBox{ 2.0, 3.0, 4.0 };                    // Define a base box
CGlassBox myGlassBox{ 2.0, 3.0, 4.0 };  // Define derived box of same size
CBox* pBox{};              // A pointer to base class objects
pBox = &myBox;           // Set pointer to address of base object
pBox->showVolume();   // Display volume of base box
pBox = &myGlassBox;  // Set pointer to derived class object

pBox->showVolume();   // Display volume of derived box

∎ Using references with virtual functions (Ex9_09)
output(myBox);           // Output volume of base class object
output(myGlassBox);  // Output volume of derived class object

void output(const CBox& aBox)  // Accept an object of any class derived from CBox as an argument
{
    aBox.showVolume();
}

∎ An abstract class (Ex9_10)
// Container.h
virtual double volume() const = 0;  // No content; pure virtual function in the abstract base class


// Main.cpp
// Pointers to abstract base class, initialized with address of CBox object or CCan object
CContainer* pC1{ new CBox{ 2.0, 3.0, 4.0 } };
CContainer* pC2{ new CCan{ 6.5, 3.0 } };

pC1->showVolume();  // Output the volumes of the two objects ...
pC2->showVolume();  // ... pointed to

delete pC1;  // Clean up ...
delete pC2;  // ... the free space

∎ More than one level of inheritance (Ex9_11)
// Class CGlassBox is derived from its direct base class CBox and indirect base class CContainer
// Inheritance & Constructor (GlassBox.h)
class CGlassBox : public CBox          
CGlassBox(double lv, double wv, double hv) : CBox{ lv, wv, hv } {}
  

∎ Calling the wrong destructor (Ex9_12) 



9.8 Casting between Class Types
∎ 


9.9 Nested Classes
∎ 


9.10 Summary
∎