Object-oriented programming · Object-oriented programming Lecture №14 Multiple inheritance 2 In C++, a class may be derived from more than one base class—a technique known as

Object-oriented programming Lecture №14

Sergey Aksenov


Multiple inheritance

2

In C++, a class may be derived from more than one base class—a technique known as multiple inheritance in which a derived class inherits the members of two or more base classes. • Multiple inheritance is a powerful capability when used properly.

Multiple inheritance should be used when an “is a” relationship exists between a new type and two or more existing types (i.e., type A “is a” type B and type A “is a” type C).

• Multiple inheritance can introduce complexity into a system. Great care is required in the design of a system to use multiple inheritance properly; it should not be used when single inheritance and/or composition will do the job. H. Daitel and P. Daitel,

C++ How to Program (5th Edition)

http://www.deitel.com/books/cpphtp5/










3

Example from www.learncpp.com

Person Employee

Teacher


http://www.learncpp.com/



4

Example from www.learncpp.com

//Person.h #include <string> class Person { private: std::string m_strName; int m_nAge; bool m_bIsMale; public: Person(std::string strName, int nAge, bool bIsMale) : m_strName(strName), m_nAge(nAge), m_bIsMale(bIsMale) { } std::string GetName() const { return m_strName; } int GetAge() const { return m_nAge; } bool IsMale() const { return m_bIsMale; } };


http://www.learncpp.com/cpp-tutorial/117-multiple-inheritance/



5

//Employee.h #include <string> class Employee { private: std::string m_strEmployer; double m_dWage; public: Employee(std::string strEmployer, double dWage) : m_strEmployer(strEmployer), m_dWage(dWage) { } std::string GetEmployer() const { return m_strEmployer; } double GetWage() const { return m_dWage; } };



6

// Teacher.h #include "Employee.h" #include "Person.h" #include <string> // Teacher publicly inherits Person and Employee class Teacher: public Person, public Employee { private: std::string m_strDegree; public: Teacher(std::string strName, int nAge, bool bIsMale, std::string strEmployer, double dWage, std::string strDegree) : Person(strName, nAge, bIsMale), Employee(strEmployer, dWage), m_strDegree(strDegree) { } };

To use multiple inheritance, simply specify each base class (just like in single inheritance), separated by a comma.

www.learncpp.com


http://www.learncpp.com/cpp-tutorial/117-multiple-inheritance/



7

// inheritance.cpp #include <string> #include <iostream> #include "Teacher.h"

void PrintPerson(const Person &person){ std::cout << person.GetName() << " is " << person.GetAge() << " years old.\n"; } double CalcTax(const Employee &employee){ return employee.GetWage()*0.14; } int main(){ Teacher teacher("Aksenov", 32, true, "MIEM", 1, "Ph.D."); PrintPerson(teacher); std::cout << "Monthly tax is " << CalcTax(teacher) << std::endl; return 0; }



8


Ambiguous access

9

#include "stdafx.h"

#include <iostream>

class Base1{

public:

int f(){return 1;}

};

class Base2{

public:

int f(){return 2;}

};

class Derived: public Base1, public Base2{

};

int main(){

Derived x;

std::cout << x.f() << std::endl;//ERROR:

//ambiguous access of 'f'

return 0;

}


Ambiguous access

10

#include "stdafx.h"

#include <iostream>

class Base1{

public:

int f(){return 1;}

};

class Base2{

public:

int f(){return 2;}

};


};

int main(){

Derived x;

std::cout << x.Base1::f() << std::endl;//OK!

return 0;

}


Ambiguous access

11

#include "stdafx.h"

#include <iostream>

class Base1{

public:

virtual int f()=0;

};

class Base2{

public:

virtual int f()=0;

};


int f(){return 0;}

};

int main(){

Derived x;

std::cout << x.f() << std::endl;//OK!

return 0;

}



12

//Person.h #include <string> class Person{ public: virtual std::string GetName()=0; virtual int GetAge()=0; virtual bool IsMale()=0; }; void PrintPerson(const Person &person); . . . __________________________________________________________________ //Person.cpp #include "Person.h" #include <iostream> void PrintPerson(const Person &person){ std::cout << person.GetName() << " is " << person.GetAge() << " years old.\n"; }



13

//Employee.h #include <string> class Employee { virtual std::string GetEmployer() = 0; virtual double GetWage() = 0; }; double CalcTax(const Employee &employee); . . . __________________________________________________________________ // Employee.cpp #include "Employee.h" double CalcTax(const Employee &employee){ return employee.GetWage()*0.14; }



14

// Teacher.h

#include "Employee.h"

#include "Person.h"

class Teacher: public Person, public Employee {

private:

std::string m_strDegree;

std::string m_strName; int m_nAge; bool m_bIsMale;

std::string m_strEmployer; double m_dWage;

public:

Teacher( std::string strName, int nAge, bool bIsMale,

std::string strEmployer, double dWage, std::string strDegree)

: m_strName(strName), m_nAge(nAge), m_bIsMale(bIsMale),

m_strEmployer(strEmployer), m_dWage(dWage), m_strDegree(strDegree){ }

// Virtual functions implementation

std::string GetName() const { return m_strName; }

int GetAge() const { return m_nAge; }

bool IsMale() const { return m_bIsMale; }

std::string GetEmployer() const { return m_strEmployer; }

double GetWage() const { return m_dWage; }

};



15

// inheritance.cpp #include <string> #include <iostream> #include "Teacher.h"

int main(){ Teacher teacher("Aksenov", 32, true, "MIEM", 1, "Ph.D."); PrintPerson(teacher); std::cout << "Monthly tax is " << CalcTax(teacher) << std::endl; return 0; }



16

class Queue {}; class CashierQueue : public Queue {}; class LunchQueue : public Queue {}; class LunchCashierQueue : public LunchQueue, public CashierQueue {};



17

class Queue {}; class CashierQueue : virtual public Queue {}; class LunchQueue : virtual public Queue {}; class LunchCashierQueue : public LunchQueue, public CashierQueue {};

Virtual base class

• The virtual keyword ensures that only one copy of the subobject Queue is included


References

• www.deitel.com

• www.learncpp.com

• msdn.microsoft.com

18

http://www.deitel.com/articles/cplusplus_tutorials/20060225/virtualBaseClass/index.html



http://www.learncpp.com/cpp-tutorial/117-multiple-inheritance

http://msdn.microsoft.com/en-us/library/wcz57btd.aspx

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Object-oriented programming · Object-oriented programming Lecture №14 Multiple inheritance 2 In C++, a class may be derived from more than one base class—a technique known as