CS225: Data Structures and Software Principles Section 4

1. CS225: Data Structures and Software PrinciplesSection 4 C++ Inheritance

2. Outline • Inheritance in C++ • Access Permissions • Constructors and Initializer Lists • Dynamic Binding and Virtual Functions • Destructors • Abstract Classes

3. Inheritance Syntax class Coord { public: Coord(); Coord(int xInit, int yInit); int getX() const; int getY() const; void print() const; private: int xCoord; // the x-value of our coordinate int yCoord; // the y-value of our coordinate }; Only Coord objects can access xCoord and yCoord directly

4. Basic Inheritance : Access Permissions LabeledCoord::LabeledCoord() : Coord(), label() { } LabeledCoord::LabeledCoord(int xInit, int yInit, String theLabel) : Coord(xInit, yInit), label(theLabel) { } class LabeledCoord : public Coord { public: LabeledCoord(); LabeledCoord(int xInit, int yInit, String theLabel); String const & getLabel() const; void print() const; private: String label; };

5. Access Permissions Members Derivation Private Protected Public

6. Derived Classes • Inherits from parent class • Every data member • Every ordinary member function • Same initial data layout • Doesn’t inherit • Constructors & destructor • Assignment operator • “Friends” • Can add data members, functions, constructors, destructor, friends

7. Dynamic Binding int main() { Coord c1(4, 5); LabeledCoord l1(3, 9, "Chicago"); c1.print(); l1.print(); Coord* cPtr = new Coord(8, 3); cPtr->print(); delete cPtr; cPtr = new LabeledCoord(7, 4, "Boston"); cPtr->print(); delete cPtr; }

8. Dynamic Binding class LabeledCoord : public Coord { public: LabeledCoord(); LabeledCoord(int xInit, int yInit, String theLabel); String const & getLabel() const; virtual void print() const; private: String label; };

9. Virtual Methods • Constructors cannot be virtual • Destructors need to be virtual • Virtual is a keyword that needs to prefix method declaration in header files, not in the .cpp file.

10. Pure Virtual Methods (Abstract Classes) class Coord { public: Coord(); Coord(int xInit, int yInit); int getX() const; int getY() const; virtual void print() const = 0; // Means you MUST implement in subclasses private: int xCoord; // the x-value of our coordinate int yCoord; // the y-value of our coordinate };