Today's Topics

1. Today's Topics • All C++ today. • Constructor initialization • Inheritance • Virtual functions • Overriding vs. hiding CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

2. Constructor Initialization the default constructor will be called for “owner” even if it is not explicitly listed This assignment stmt happens after all the initialization • Order of initialization: • name = n • weight = 0 • owner public class Pet { string name; int weight; Person owner; } Pet::Pet(string n) : owner(), name(n) { weight = 50; … } CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

3. Constructor Initialization • Sometimes initialization must be done in the initialization list: Person has no default constructor, so we can’t let owner() be called; breed is a constant string, so it cannot occur on the left hand side of an assignment statement veterinarian is a reference type, so also cannot occur on the left hand side of an assignment statement class Person { string name; Person(string n) { name = n; } } class Pet { Person owner; const string breed; Person& veterinarian; } Pet::Pet(Person ownr, string brd, Person vet) : owner(ownr), breed(brd), veterinarian(&vet) { … } CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

4. C++ Inheritance • Syntax is different from Java: • class class-name: public base-name • { • member declarations • }; • There is also private and protected derivation, rarely used; unfortunately, private is the default. CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

5. C++ Inheritance • Example: • class Student • { • public: • Student(string nm, int id); • void Print(); • protected: • string name; • int student_id; • }; CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

6. C++ Inheritance • class GradStudent : public Student • { • public: • GradStudent(string nm, int id, string th); • void Print(); • protected: • string thesis; • }; CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

7. C++ Inheritance • GradStudent is the derived class. • Student is the base class. • Public derivation has these characteristics: • protected and public members of Student are inherited as protected and public members of GradStudent. • Only constructors, destructors, and the member function operator=() cannot be inherited. • Private members of Student are inaccessible. • GradStudent is a subtype of Student (is-a relationship. CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

8. Inheritance and Constructors Note: The constructor of Student is invoked as part of the initializer list in the constructor of GradStudent. • Implementation of constructors: • Student::Student(string nm, int id) • : name(nm), student_id(id) {} • GradStudent::GradStudent(string nm, int id, string th) • : Student(nm, id), thesis(th) {} CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

9. Pointer Type Conversions • A reference to the derived class can be implicitly converted to a reference to the public base class. • Example: • GradStudent gst(“John Smith”, 31416, • “Verification of Network Protocols”); • Student &st = gst; CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

10. Visibility • Print() member functions for Student and GradStudent: • void Student::Print() const • { • cout << name << “ , “ << student_id << endl; • } • void GradStudent::Print() const • { • Student::Print(); • cout << thesis << endl; • } CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

11. Pointer Types and Visibility • Example for pointer conversions: • Student s(“Joe Smith”, 111); • Student *ps = &s; • GradStudent gs(“John Smith”, 31416, • “Verification of Network Protocols”); • GradStudent *pgs; • ps->Print(); • ps = pgs = &gs; • pgs->Print(); • ps->Print(); • // Student::Print() • // GradStudent::Print() • // Student::Print() CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

12. Visibility, continued illegal • Visibility is determined at compile-time: • class Pet {…}; • class Dog : public Pet { • virtual void dig(); • } • … • int main() { • Pet *ptrPet = new Dog(); • ptrPet->dig(); • } dig is not defined for class Pet, only for subclass Dog, and ptrPet is of type pointer-to-Pet CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

13. Hiding versus Overriding • class Student { • public: • void Print() const; • virtual void Vprint() const; • year yr; //year is enum type • … • }; • class GradStudent : • public Student { • public: • void Print() const; • virtual void Vprint() const; • int yr; • … • } • int main() { • GradStudent gs= • new GradStudent(); • Student *pstudent = &gs; • pstudent->Print(); • pstudent->Vprint(); • pstudent->yr = 2006; • pstudent->yr = senior; • } Student::Print() GradStudent::Vprint() Illegal Legal Print() and yr are hidden in GradStudent Vprint() is overridden in GradStudent CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

14. Overloading versus overriding class Diffident { public: virtual void mumble(int softness); … }; class Shy : public Diffident { public: virtual void mumble(string whatYaSay); … }; … Shy simon; simon.mumble(“pardon me”); simon.mumble(2); Ok Illegal-- int arg function is hidden CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

15. Multiple Inheritance • In C++, a class can inherit from two or more base classes: ZooAnimal class ZooAnimal {..}; class Endangered {…}; class Bear :public ZooAnimal {…}; class Panda :public Bear, public Endangered {…}; Bear Endangered Panda CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions

16. Multiple Inheritance: Iostream virtual inheritance Because istream, ostream inherit virtually, iostream has only one copy of ios • Multiple inheritance occurs with the standard iostream library. ios istream ostream ifstream iostream ofstream fstream CS410 – Software Engineering C++ Initialization, Inheritance and Virtual Functions