1. Advanced C++ Topics
Chapter 8

2. Chapter 8 -- Advanced C++ Topics
This chapter describes techniques that make collections of reusable software components possible.
Inheritance
Virtual Functions and Late Bindings
Friends
Class Templates
Overloaded Operators
Iterators
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3. Inheritance Revisited
Inheritance is a relationship among classes.
One class can derive the behavior and structure of another class.
On the next page we see relationships among timepieces
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A digital alarm clock is a digital clock
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Def: derived class (subclass)
Def: base class (superclass)
In C++, a derived class inherits all the members of its base class, excepts the constructors and destructor.
Some languages allow you to have more than 1 base class.
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Inheritance allows you to reuse software components when you define a new class.
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Class Sphere{
public:
Sphere();
Sphere(double initialRadius);
void SetRadius(double newRadius);
double getRadius() const;
double getDiameter() cosnt;
double getCircumference();
double getArea() const;
double getVolume() const;
double displayStatistics() const;
private:
double theRadius; };
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Class Ball: public Sphere {
public:
Ball();
Ball(double initialRadius, cosnt string initialName);
void getName(string currentName) const;
void setName(const string newName);
void resetBall(double newRadius, const string newName);
double displayStatistics() const;
private:
string theName; };
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Ball::Ball() : Sphere()
{ setName(“”); }
Ball::Ball(double initialRadius, const string initialName): Sphere(initialRadius)
{ setName(initialName);}
void Ball::resetBall(double newRadius, const string newName) {
setRadius(newRadius);
setName(newName); }
void Ball::displayStatistics() const
{ cout << “statistics for a “<< theName << “:”;
Sphere::displayStatistics(); }
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Ball myBall(5.0, “Volleyball”);
Sphere myShpere();
The compiler can tell which function to use at compile time and this is called early binding or static binding
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A derived class’s constructor executes after the base class’s constructor.
Built inside out
The destructor of the derived class executes before the destructor of the base class.
Destroyed outside in
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Addition of the protected section
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Public, Private, and Protected Inheritance
Several kinds of inheritance are possible.
The key is -- if you have layers of inheritance, how are the lower layers treated.
Public inheritance
Public and protected members of the base class remain public and protected members of the derived class
Protected inheritance
Public and protected members of the base class are protected members of the derived class
Private inheritance
Public and protected members of the base class are private members of the derived class.
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Is-a, Has-a, and As-a Relationships
Is-a relationships - public inheritance
A Ball is a Sphere
Whatever is true of type sphere is also true of type ball
This is called object type compatibility
void displayDiameter(Sphere thing) {
cout << “The diameter is “
<< thing.getDiameter() << “.\n”; }
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If you define mySphere and myBall as
Sphere mySphere(2.0);
Ball myBall(5.0, “Volleyball”);
The following calls are legal:
displayDiameter(mySphere);
displayDiameter(myBall);
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Has-a relationship
A ball point pen has a ball
class Pen {
...
Private:
Ball point; };
Thus another name for the has-a relationship is containment.
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As-a relationship
You can implement a Stack as a list
class Stack: private List
Thus within the Stack you can manipulate the list by using list’s methods.
Both descendants and clients of stack, however, would not be able to access any members of List.
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18. Virtual Functions and Late Binding
Example:
Case 1:
Sphere *spherePtr = &mySphere
spherePtr->displayStatistics();
Case 2:
spherePtr = &myBall;
What is the difference, what functions get called?
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Answer: They both invoke sphere’s version of displayStatistics() because of early binding.
We need to tell the compiler that the function might be changed so it will not bind at compile time but will wait until run-time to see which one to call.
You do this with the keyword virtual
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In the base class you do it this way
class Sphere{
public:
...
virtual void displayStatistics() const; };
Now the compiler will do late binding or dynamic binding.
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displayStatistics is called a polymorphic function
polymorphism means many forms.
We also say that Balls’ version of displayStatistics overrides Sphere’s version
Now let’s look at some examples of how early and late binding can interact.
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Assume display statistics is virtual and getArea is not.
Now if it is ....
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Abstract Base Classes
If your base class has a virtual function that all of its descendants will have to overload,
you can give just a prototype and no code
This is called a pure virtual function
virtual void setRadius(double newRadius) = 0;
Any class with pure virtual functions (or a derived class that has not defined all pure virtual functions) is called an Abstract Base class, and no instances of it can be declared.
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Friends
Declaring a non-member function as a friend to a class allows that function to access all the private members of the class
For example: input and output functions are often defined as friend functions
You also saw class fiends in your linked list nodes.
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Class Templates
You can avoid multiple class definitions by using a C++ class template to specify a class in terms of a data-type parameter.
You have used templates since the middle of CS 202
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Overloaded Operators
An operator with more than one meaning is said to be overloaded and is an example of a simple form of polymorphism
To overload an operator, you define an operator function whose name has the form
operator symbol
where symbol is the operator that you want to overload
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Iterators
An iterator traverses a collection of objects
Typically an iterator has an operation that accesses the item it currently references.
Usually this is implemented by overloading the dereference operator, *
Iterators also have operations that move the iterator forward and backward through a collection (++, --). They also usually have == and != overloaded as well.
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