Which member function can only be called by another function that is member of its class?

Which of the following means "The use of an object of one class in definition of another class"?

Answer: Option C

Explanation:

No answer description available for this question. Let us discuss.

Which of the following is the only technical difference between structures and classes in C++?

Answer: Option C

Explanation:

No answer description available for this question. Let us discuss.

Which of the following is not the member of class?

Answer: Option B

Explanation:

No answer description available for this question.

One more thing is that const memb function can modify only those data members that are declared as mutable.

These are functions of the class and belong to the class. However, a friend function is one such type of function which can access the private data members of a class and is not a MEMBER function.

Why do we need them? 'cause there are times when you need to access private data members with an external function. Using too many friend functions disintegrates the privacy of the object. They should be used only when necessary.

Base class pointer can point to derived class object. In this case, using base class pointer if we call some function which is in both classes, then base class function is invoked. But if we want to invoke derived class function using base class pointer, it can be achieved by defining the function as virtual in base class, this is how virtual functions support runtime polymorphism.

Consider following program code:

Class A
{
int a;
public:
A()
{
a = 1;
}
virtual void show()
{
cout <<a;
}
};

Class B: public A
{
int b;
public:
B()
{
b = 2;
}
virtual void show()
{
cout <<b;
}
};

int main()
{
A *pA;
B oB;
pA = &oB;
pA->show();
return 0;
}

Output is 2 since pA points to object of B and show() is virtual in base class A.

using namespace std;

class Box
{
double width;
public:
friend void printWidth( Box box );
void setWidth( double wid );
};

// Member function definition
void Box::setWidth( double wid )
{
width = wid;
}

// Note: printWidth() is not a member function of any class.
void printWidth( Box box )
{
/* Because setWidth() is a friend of Box, it can
directly access any member of this class */
cout << "Width of box : " << box.width <<endl;
}

// Main function for the program
int main( )
{
Box box;

// set box width without member function
box.setWidth(10.0);

// Use friend function to print the wdith.
printWidth( box );

return 0;
}

So what is the requirement of show as virtual function?

Friend function can access the private & protected data of the parent class!

Normally, Other class couldn't able to access the private & protected data of a class.