Virtual function

[bintom]

In the first program, given below, I have to make "father" and
"mother" virtual. However, in the second program, even without
declaring the classes virtual, the program works. Why?

//
***********************************************************************************
// 1st Program

class person
{ char name[21]; int age;
public : void init(char *n, int a) { strcpy(name, n); age = a; }
char* get_name() { return name; }
int get_age() { return age; }
};

class father : virtual public person
{ char sport[11];
public : void init(char *n, int a, char *sp)
{ person :: init(n, a);
strcpy(sport, sp);
}
char* get_sport() { return sport; }
};

class mother : virtual public person
{ char pasttime[16];
public : void init(char *n, int a, char *p)
{ person :: init(n, a);
strcpy(pasttime, p);
}
char* get_pasttime() { return pasttime; }
};

class child : public father, public mother
{ char school[21];
public : void init(char *n, int a, char *sp, char *p, char *sc)
{ father :: init(n, a, sp);
mother :: init(n, a, p);
strcpy(school, sc);
}
char* get_school()
{ return school; }
};

int main()
{ person p; p.init("Jack", 23);
cout << p.get_name() << " " << p.get_age() << endl;

father f; f.init("Papa", 45, "Cricket");
cout << f.get_name() << " " << f.get_age() << " " << f.get_sport()
<< endl;

mother m; m.init("Mama", 42, "Gardening");
cout << m.get_name() << " " << m.get_age() << " " <<
m.get_pasttime() << endl;

child c; c.init("Kiddo", 12, "Kabaddi", "Bird watching", "BCRS");
cout << c.get_name() << " " << c.get_age() << " " << c.get_sport()
<< " "
<< c.get_pasttime() << " " << c.get_school() << endl;
}




//
***********************************************************************************
// 2nd Program

class Point
{ private: int x, y;
public : void setX(int X) { x = X; }
int getX() { return x; }
void setY(int Y) { y = Y; }
int getY() { return y; }
void moveX(int i) { setX(getX() + i); }
};

class Circle : public Point
{ private: float radius;
public : void setR(float R) { radius = R; }
float getR() { return radius; }
};

class Square : public Point
{ private: float side;
public : void setSide(float S) { side = S; }
float getSide() { return side; }
};

class Shape : public Circle, public Square
{ private: int color;
public : void setColor(int C) { color = C; }
int getColor() { return color; }
};

void shiftY(Point &P, int i)
{ P.setY(P.getY() + i); }

int main()
{ Square S1; S1.setX(9); S1.setY(4); S1.setSide(5.85);
cout << S1.getX() << ", " << S1.getY() << ", " << S1.getSide() <<
"\n";
S1.moveX(11);
cout << S1.getX() << ", " << S1.getY() << ", " << S1.getSide() <<
"\n";
shiftY(S1, 3);
cout << S1.getX() << ", " << S1.getY() << ", " << S1.getSide() << "\n
\n";
}

 

[Kalle Olavi Niemitalo]

In the first program, given below, I have to make "father" and
"mother" virtual. However, in the second program, even without
declaring the classes virtual, the program works. Why?

The second program does not declare any object of type Shape.
If you changed "Square S1" to "Shape S1", then the S1.setX(9)
call would become ambiguous, as would many others.

 

[bintom]

Hi Kalle Olavi Niemitalo,

Thanks a ton!!

BinTom