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BY EXAMPLES

Inheritance

Saras M. Srivastava

PGT – Comp. Sc.Kendriya Vidyalaya

Air Force Station Makarpura,Vadodara - 390014

LEARN

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class PUBLISHER {

char pub[12];double turnover;protected:void register( );public:PUBLISHER( );void enter( );void display( );

};

Example1

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class BRANCH {

char city[20];protected:

float employees; public:

BRANCH( );void haveit( );void giveit( );

};

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class AUTHOR: private BRANCH, public PUBLISHER

{int acode;char aname[20];float amount;

public:AUTHOR( );void start( );void show( );

};

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Write the names of data members. Which are accessible from objects belonging to class AUTHOR.

Write the names of all the member functions which are accessible from objects belonging to class BRANCH.

Write the names of all the members which are accessible from member functions of class AUTHOR.

How many bytes will be required by an object belonging to class AUTHOR?

Questions

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class Mydata { protected:

int data;public:

void Get_mydata(int);void Manip_mydata(int);void Show_mydata(int);Mydata( );~Mydata( );

};

Example 2

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class Personal_data{protected:

int data1;public:

void Get_personaldata(int);void Show_personaldata(int);Personal_data( );~Personal_data( );

};

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class Person: public Mydata, Personal_data{

public:void Show_person(void);Person( );~Person( );

};

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i) How many bytes will be required by an object belonging to class Person?

ii) Which type of inheritance is depicted in the above example?

iii) List the data members that can be accessed by the member function Show_person( ).

iv) What is the order of constructor execution at the time of creating an object of class Person?

Questions

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class Goods { int id;protected :char name[20];long qty;void Incr(int n);public :Goods();~Goods();void get(); };

Example 3

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class Food_products : public Goods{

char exp_dt[10];protected :

int id;int qty;

public :void getd();void showd();

};

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class Cosmetics : private Goods{

int qty;char exp_date[10];

protected :int id;

public :~Cosmetics();Cosmetics();void show();

};

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(i) How many bytes will be required by an object of class Food_products.

(ii) Name the member functions accessible through the object of class Food_products.

(iii) From the following, Identify the member function(s) that cannot be called directly from the object of class Cosmeticsshow(), getd(), get()

(iv) If the class cosmetics inherits the properties of food_products class also, then name the type of inheritance.

Questions

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class livingbeing{

char specification[20];int averageage;

public:void read();void show();

};

Example 4

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class ape : private livingbeing{ int no_of_organs, no_of_bones; protected:

int iq_level; public:

void readape();void showape();

};

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class human : public ape{

char race[20];char habitation[30];

public:void readhuman();void showhuman();

};

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a. Name the members which can be accessed from the member functions of class human.

b. Name the members, which can be accessed by an object of class human.

c. What will be the size of an object (in bytes) of class human.

d. Name the class(es) that can access read() declared in livingbeing class.

Questions

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class vehicle{ int wheels;

protected:int passenger;

public:void inputdata();void outputdata();

};

Example 5

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class heavyvehicle : protected vehicle{ int diesel_petrol;

protected:int load;public:void readdata(int, int);void writedata();

};

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class bus : private heavyvehicle{ char make[20];

public:void fetchdata();void displaydata();

};

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Name the base class and derived class of heavyvehicle class.

Name the data member(s) that can be accessed from the function displaydata().

How many bytes will be required by an object of vehicle and heavyvehicle classes respectively?

Is the member function outputdata() accessible to the objects of the class heavyvehicle?

Questions

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RectangleTriangle

Polygon

class Polygon{protected: int numVertices; float *xCoord, float *yCoord;public: void set(float *x, float *y, int nV);

};

class Rectangle : public Polygon{public: float area();

};

class Rectangle{protected: int numVertices; float *xCoord, float *yCoord;public: void set(float *x, float *y, int nV); float area();

};

Inheritance Concept

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RectangleTriangle

Polygon

class Polygon{protected: int numVertices; float *xCoord, float *yCoord;public: void set(float *x, float *y, int nV);

};

class Triangle : public Polygon{public: float area();

};

class Triangle{protected: int numVertices; float *xCoord, float *yCoord;public: void set(float *x, float *y, int nV); float area();

};

Inheritance Concept

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Inheritance ConceptPoint

Circle 3D-Point

class Point{protected: int x, y;public: void set (int a, int b);

};

class Circle : public Point{private:

double r;};

class 3D-Point: public Point{private:

int z;};

xy

xyr

xyz

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Augmenting the original class

Specializing the original class

Inheritance Concept

RealNumber

ComplexNumber

ImaginaryNumber

Rectangle Triangle

Polygon Point

Circle 3D-Point

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Why Inheritance ?

Inheritance is a mechanism for

building class types from existing class types

defining new class types to be a specialization augmentation of existing types

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Define a Class Hierarchy

Syntax:class DerivedClassName : access-level BaseClassName

where access-level specifies the type of derivation

private by default, orpublic

Any class can serve as a base classThus a derived class can also be a base class

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Class DerivationPoint

3D-Point

class Point{protected: int x, y;public: void set (int a, int b);

};

class 3D-Point : public Point{private:

double z;… …

};

class Sphere : public 3D-Point{private:

double r;… …

};

Sphere

Point is the base class of 3D-Point, while 3D-Point is the base class of Sphere

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What to inherit?

In principle, every member of a base class is inherited by a derived class just with different access permission

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Access Control Over the MembersTwo levels of access

control over class membersclass definitioninheritance type

base c lass / superc lass /pa ren t c lass

de riv ed c lass / subc lass /ch ild c lass

deriv

e fro

m

mem

bers

goe

s to

class Point{protected: int x, y;public: void set(int a, int b);

};class Circle : public Point{

… …};

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The type of inheritance defines the access level for the members of derived class that are inherited from the base class

Access Rights of Derived Classes

private protected publicprivate - - -protected private protected protectedpublic private protected public

Type of Inheritance

Access C

ontrolfor M

embers

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class daughter : --------- mother{private: double dPriv;public: void mFoo ( );

};

Class Derivationclass mother{

protected: int mProc;public: int mPubl;private: int mPriv;

};

class daughter : --------- mother{private: double dPriv;public: void dFoo ( );

};void daughter :: dFoo ( ){

mPriv = 10; //errormProc = 20;

};

private/protected/public int main() {

/*….*/}

class grandDaughter : public daughter {private: double gPriv;public: void gFoo ( );

};

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What to inherit?In principle, every member of a base class

is inherited by a derived class just with different access permission

However, there are exceptions forconstructor and destructor friendsSince all these functions are class-specific

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Constructor Rules for Derived Classes

The default constructor and the destructor of the

base class are always called when a new object of a

derived class is created or destroyed.

class A { public:

A ( ) {cout<< “A:default”<<endl;}A (int a) {cout<<“A:parameter”<<endl;}

};

class B : public A { public:

B (int a) {cout<<“B”<<endl;}

};

B test(1);A:defaultB

output:

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Constructor Rules for Derived Classes You can also specify an constructor of the base class other than the default constructor

class A { public:

A ( ) {cout<< “A:default”<<endl;}A (int a) {cout<<“A:parameter”<<endl;}

};

class C : public A { public:

C (int a) : A(a) {cout<<“C”<<endl;}

};

C test(1);A:parameterC

output:

DerivedClassCon ( derivedClass args ) : BaseClassCon ( baseClass args )

{ DerivedClass constructor body }

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Define its Own Members

Point

Circle

class Point{protected: int x, y;public: void set(int a, int b);

};

class Circle : public Point{private:

double r;public:

void set_r(double c);

};

xy

xyr

class Circle{ protected:

int x, y;private: double r;public: void set(int a, int b); void set_r(double c);

};

The derived class can also define its own members, in addition to the members inherited from the base class

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Even more …A derived class can override methods defined

in its parent class. With overriding, the method in the subclass has the identical

signature to the method in the base class. a subclass implements its own version of a base class

method. class A { protected:

int x, y; public:

void print (){cout<<“From

A”<<endl;}};

class B : public A { public:

void print () {cout<<“From B”<<endl;}

};

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class Point{protected: int x, y;public: void set(int a, int b)

{x=a; y=b;} void foo (); void print();

};

class Circle : public Point{ private: double r; public:

void set (int a, int b, double c) { Point :: set(a, b); //same name function call r = c;}void print(); };

Access a Method

Circle C;C.set(10,10,100); // from class CircleC.foo (); // from base class PointC.print(); // from class Circle

Point A;A.set(30,50); // from base

class PointA.print(); // from base class

Point

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Putting Them TogetherTime is the base classExtTime is the derived class

with public inheritanceThe derived class can

inherit all members from the base class, except the constructor

access all public and protected members of the base class

define its private data member provide its own constructor define its public member

functions override functions inherited

from the base class

ExtTime

Time

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class Time Specificationclass Time{ public :

void Set ( int h, int m, int s ) ;void Increment ( ) ;void Write ( ) const ;Time ( int initH, int initM, int initS ) ; // constructor Time ( ) ; // default constructor

protected :int hrs ; int mins ; int secs ;

} ;

// SPECIFICATION FILE ( time.h)

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Class Interface Diagram

Protected data:hrs

mins

secs

Set

Increment

Write

Time

Time

Time class

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Derived Class ExtTime // SPECIFICATION FILE ( exttime.h)

#include “time.h”enum ZoneType {EST, CST, MST, PST, EDT, CDT, MDT, PDT } ;

class ExtTime : public Time // Time is the base class and use public inheritance

{ public :

void Set ( int h, int m, int s, ZoneType timeZone ) ;void Write ( ) const; //overridden

ExtTime (int initH, int initM, int initS, ZoneType initZone ) ;

ExtTime (); // default constructor

private :ZoneType zone ; // added data member

} ;

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Class Interface Diagram

Protected data:hrs

mins

secs

ExtTime class

Set

Increment

Write

Time

Time

Set

Increment

Write

ExtTime

ExtTime

Private data:zone

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Implementation of ExtTime

Default Constructor

ExtTime :: ExtTime ( )

{ zone = EST ;

}The default constructor of base class, Time(), is automatically called, when an ExtTime object is created.

ExtTime et1;

hrs = 0mins = 0secs = 0zone = EST

et1

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Implementation of ExtTimeAnother Constructor

ExtTime :: ExtTime (int initH, int initM, int initS, ZoneType initZone) : Time (initH, initM, initS) // constructor initializer

{ zone = initZone ;}

ExtTime *et2 = new ExtTime(8,30,0,EST); hrs = 8

mins = 30secs = 0zone = EST

et2

5000

???6000

5000

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Implementation of ExtTimevoid ExtTime :: Set (int h, int m, int s, ZoneType timeZone) { Time :: Set (hours, minutes, seconds); // same name function

call

zone = timeZone ;}

void ExtTime :: Write ( ) const // function overriding{ string zoneString[8] =

{“EST”, “CST”, MST”, “PST”, “EDT”, “CDT”, “MDT”, “PDT”} ;

Time :: Write ( ) ; cout <<‘ ‘<<zoneString[zone]<<endl;}

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Working with ExtTime #include “exttime.h”

… …int main()

{ ExtTime thisTime ( 8, 35, 0, PST ) ; ExtTime thatTime ; // default constructor calledthatTime.Write( ) ; // outputs 00:00:00 ESTthatTime.Set (16, 49, 23, CDT) ; thatTime.Write( ) ; // outputs 16:49:23 CDTthisTime.Increment ( ) ;thisTime.Increment ( ) ;thisTime.Write ( ) ; // outputs 08:35:02 PST}

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Take Home MessageInheritance is a mechanism for defining new

class types to be a specialization or an augmentation of existing types.

In principle, every member of a base class is inherited by a derived class with different access permissions, except for the constructors

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QUESTIONS