CSC 213 Code Chapter 9, Fall 2007

Inheritance 1 Circle::Circle(double r, int a, int b) : Point(a,b) { ... ... }; Using Constructors and Destructors in Derived Classes • Knowing that a derived-class inherits its base-class’ members… When an object of a derived class is instantiated, the base-class’ constructor must be called… • A base-class initializer can be provided in the derived class constructor to call the base-class constructor explicitly… Otherwise base class’s default constructor called implicitly… • Base-class constructor and base-class assignment operators are not inherited by derived-class… however derived-class can call base-class constructor and assignment operator… Inheritance 2 class ABase { public: ABase(int a) { x = a; } void setX(int a) { x = a; } void operator =(int a) { x = a; } void operator -=(int i) {x -= i;} void operator +=(int i) {x += i;} private: int x; }; class ADerived : public ABase { public: ADerived(int a, int b) : ABase(b){y = a;} void operator +=(int i) {y += i;} void operator =(ABase &aB) { aB = y; // Called not inherited…[JAN1] } private: int y; }; void main() { ABase basObj(10); ADerived drvObj(20,30); basObj = 50; drvObj = basObj; basObj +=10; basObj -=2; drvObj +=10; drvObj -=2; drvObj.setX(10); drvObj = 100; } Syntax Error… base-class assignment operators are not inherited by derived-class Inheritance 3 Implicit Derived-Class Object to Base-Class Object Conversion • Even though a derived-class object iiss__aa base-class object, the derived-class type and the base-class type are different… • Derived-class object can be treated as a base-class object… ! Derived class has members corresponding to all of the base class’s members… Thus, base-class can be assigned a derived-class… ! Needless to say, that derived-class may have more members than the base-class object… • Base-class object cannot be treated as a derived-class object… ! Would leave additional derived class members undefined…Thus derived-class cannot be assigned a base-class… ! Obviously, assignment operator can be overloaded to allow such an assignment… Inheritance 4 z #include <iostream.h> class ABase { public: ABase(int a) { x = a; } int getX() const {return x;} protected: int x; }; class ADerived : public ABase { public: ADerived(int a, int b) : ABase(b){ y = a; } void operator =(ABase &aB) { y = aB.getX(); } private: int y; }; void main() { ABase basObj(10); ADerived drvObj(20,30); drvObj = basObj; basObj = drvObj; } Syntax Error, without the assignment operator overloaded… Inheritance 5 • Mixing base and derived class pointers and objects ! Referring to a base-class object with a base-class pointer # # allowed… ! Referring to a derived-class object with a derived- class pointer # # allowed… ! Referring to a derived-class object with a base- class pointer # # allowed for base-class members… The derived-class object is an object of its base-class as well… # # Syntax error for derived class members… ! Referring to a base-class object with a derived- class pointer # # Syntax error…The derived-class pointer must first be cast to a base-class pointer… Inheritance 6 #include <iostream.h> class ABase { public: ABase(int a) { x = a; } void printX() const {cout << x <<endl;} protected: int x; }; class ADerived : public ABase { public: ADerived(int a, int b):ABase(b){y = a;} void printY() const {cout << y <<endl;} private: int y; }; void main() { ABase *basPtr, basObj(10); ADerived *drvPtr, drvObj(20,30); basPtr = &basObj; basPtr ->printX(); drvPtr = &drvObj; drvPtr->printY(); drvPtr->printX(); basPtr = &drvObj; basPtr->printX(); basPtr->printY(); drvPtr = &basObj; drvPtr = static_cast<ADerived *>(&basObj); drvPtr->printX(); drvPtr->printY(); } Syntax Error… Inheritance 7 class A { public : void f1(){ x=x; } protected: int x; }; class B:public A { protected: int y; public : void f1(){ y=y; } }; class C:public A { protected: int z; public : void f1(){ z=z; } }; class ABC:public B, public C { protected: int xyz; }; void main () { ABC abc; abc.f1(); } Problems with Multiple Inheritance ??