Multiple Inheritance in C++

#include<iostream>using namespace std;class Person {public:    Person(int x)  { cout << "Person::Person(int ) called" << endl;   }    Person()     { cout << "Person::Person() called" << endl;   }}; class Faculty : virtual public Person {public:    Faculty(int x):Person(x)   {       cout<<"Faculty::Faculty(int ) called"<< endl;    }}; class Student : virtual public Person {public:    Student(int x):Person(x) {        cout<<"Student::Student(int ) called"<< endl;    }}; class TA : public Faculty, public Student  {public:    TA(int x):Student(x), Faculty(x)   {        cout<<"TA::TA(int ) called"<< endl;    }}; int main()  {    TA ta1(30);}

Output:

Person::Person() calledFaculty::Faculty(int ) calledStudent::Student(int ) calledTA::TA(int ) called

In the above program, constructor of ‘Person’ is called once. One important thing to note in the above output is, the default constructor of ‘Person’ is called. When we use ‘virtual’ keyword, the default constructor of grandparent class is called by default even if the parent classes explicitly call parameterized constructor.

How to call the parameterized constructor of the ‘Person’ class? The constructor has to be called in ‘TA’ class. For example, see the following program.

#include<iostream>using namespace std;class Person {public:    Person(int x)  { cout << "Person::Person(int ) called" << endl;   }    Person()     { cout << "Person::Person() called" << endl;   }}; class Faculty : virtual public Person {public:    Faculty(int x):Person(x)   {       cout<<"Faculty::Faculty(int ) called"<< endl;    }}; class Student : virtual public Person {public:    Student(int x):Person(x) {        cout<<"Student::Student(int ) called"<< endl;    }}; class TA : public Faculty, public Student  {public:    TA(int x):Student(x), Faculty(x), Person(x)   {        cout<<"TA::TA(int ) called"<< endl;    }}; int main()  {    TA ta1(30);}

Output:

Person::Person(int ) calledFaculty::Faculty(int ) calledStudent::Student(int ) calledTA::TA(int ) called

In general, it is not allowed to call the grandparent’s constructor directly, it has to be called through parent class. It is allowed only when ‘virtual’ keyword is used.

Ref http://www.geeksforgeeks.org/multiple-inheritance-in-c/