IN C++ To gain a better understanding of polymorphic and virtual functions start with the following simple example. Notice we have not defined a virtual function yet. // Part1.h. Note, this header file will have TWO classes declared. #include using namespace std; class Base { public: void testFunction (); }; class Derived : public Base { public: void testFunction (); }; // Part1.cpp. Note this implementation file will have TWO class defined. #include "Part1.h" void Base::testFunction () { cout << "Base class" << endl; } void Derived::testFunction () { cout << "Derived class" << endl; } // main.cpp #include "Part1.h" int main() { Base* ptr = new Base; ptr -> testFunction (); // prints "Base class" delete ptr; ptr = new Derived; ptr -> testFunction (); // prints "Base class" because the base class // function is not virtual delete ptr; return 0; } Now modify the code with the following (all other code should remain the same). class Base { public: virtual void testFunction (); }; Compile and run your program with this modification. You’ll notice the second testFunction() call generates the message “Derived class”. Welcome to polymorphism! No need to submit anything for this part of the lab, just make sure that virtual is clear to you. You will build two classes, Mammal and Dog. Dog will inherit from Mammal. Below is the Mammal class code. Once you have the Mammal class built, build a second class Dog that will inherit publicly from Mammal. The Dog class should also override the move() and speak() methods from Mammal. // Mammal.h class Mammal { public: Mammal(); ~Mammal(); virtual void move() const; virtual void speak() const; protected: int itsAge; }; // Mammal.cpp #include "Mammal.h" Mammal::Mammal():itsAge(1) { cout << "Mammal constructor..." << endl; } Mammal::~Mammal() { cout << "Mammal destructor..." << endl; } void Mammal::move() const { cout << "Mammal moves a step!" << endl; } void Mammal::speak() const { cout << "What does a mammal speak? Mammilian!" << endl; } Once you have completed class Mammal and Dog, build the following main program. #include "Mammal.h" #include "Dog.h" int main () { Mammal *pDog = new Dog; pDog->move(); pDog->speak(); //Dog *pDog2 = new Dog; //pDog2->move(); //pDog2->speak(); delete pDog; //delete pDog2; return 0; } What does it output, and is that what you expected? Remove the keyword virtual from the Mammal class and try it again. Now what happens? Next, put in another pointer to pDog2 in the main program, but this time make it a pointer to a Dog, not a Mammal and create a new Dog (as seen in code comments). Now what happens? What you should realize is that by making the method speak() virtual, we can have a bit different behavior through dynamic (runtime) binding. Develop additional classes for Cat, Horse, and GuineaPig overriding the move() and speak() methods. (If you didn’t know, guinea pigs go “wheep wheepLinks to an external site.”). Make sure to also define a constructor and destructor for each of these classes, and that when you run your program, you can also see that the correct constructors and destructors are being called. Recall that a derived class will always call the parents constructors and destructors, so if you see this behavior, that is okay. Just make sure you are also calling the derived class’ constructors and destructors. Test with the modified main: int main () { Mammal* theArray[5]; Mammal* ptr; int choice; for (int i = 0; i < 5; i++) { cout << "(1)dog (2)cat (3)horse (4)guinea pig: "; cin >> choice; switch (choice) { case 1: ptr = new Dog; break; case 2: ptr = new Cat; break; case 3: ptr = new Horse; break; case 4: ptr = new GuineaPig; break; default: ptr = new Mammal; break; } theArray[i] = ptr; } // Iterate through array, and have each animal speak for (int i = 0; i < 5; i++) { theArray[i]->speak(); } // Always free dynamically allocated objects for (int i = 0; i < 5; i++) { delete theArray[i]; } return 0; } Sample run: (1)dog (2)cat (3)horse (4)guinea pig: 1 Mammal constructor... Dog constructor... (1)dog (2)cat (3)horse (4)guinea pig: 2 Mammal constructor... Cat constructor... (1)dog (2)cat (3)horse (4)guinea pig: 3 Mammal constructor... Horse constructor... (1)dog (2)cat (3)horse (4)guinea pig: 4 Mammal constructor... Guinea Pig constructor... (1)dog (2)cat (3)horse (4)guinea pig: 5 Mammal constructor... What does a dog say? Woof! What does a cat say? Meow! What does a horse say? Neigh! What does a Guinea Pig say? Wheep WHEEP! What does a mammal speak? Mammilian! Dog destructor... Mammal destructor... Cat destructor... Mammal destructor... Horse destructor... Mammal destructor... Guinea Pig destructor... Mammal destructor... Mammal destructor...
IN C++
- To gain a better understanding of polymorphic and virtual functions start with the following simple example. Notice we have not defined a virtual function yet.
// Part1.h. Note, this header file will have TWO classes declared.
#include <iostream>
using namespace std;
class Base
{
public:
void testFunction ();
};
class Derived : public Base
{
public:
void testFunction ();
};
// Part1.cpp. Note this implementation file will have TWO class defined.
#include "Part1.h"
void Base::testFunction ()
{
cout << "Base class" << endl;
}
void Derived::testFunction ()
{
cout << "Derived class" << endl;
}
// main.cpp
#include "Part1.h"
int main()
{
Base* ptr = new Base;
ptr -> testFunction (); // prints "Base class"
delete ptr;
ptr = new Derived;
ptr -> testFunction (); // prints "Base class" because the base class
// function is not virtual
delete ptr;
return 0;
}
Now modify the code with the following (all other code should remain the same).
class Base
{
public:
virtual void testFunction ();
};
Compile and run your program with this modification. You’ll notice the second testFunction() call generates the message “Derived class”. Welcome to polymorphism! No need to submit anything for this part of the lab, just make sure that virtual is clear to you.
-
You will build two classes, Mammal and Dog. Dog will inherit from Mammal. Below is the Mammal class code. Once you have the Mammal class built, build a second class Dog that will inherit publicly from Mammal. The Dog class should also override the move() and speak() methods from Mammal.
// Mammal.h
class Mammal
{
public:
Mammal();
~Mammal();
virtual void move() const;
virtual void speak() const;
protected:
int itsAge;
};
// Mammal.cpp
#include "Mammal.h"
Mammal::Mammal():itsAge(1)
{
cout << "Mammal constructor..." << endl;
}
Mammal::~Mammal()
{
cout << "Mammal destructor..." << endl;
}
void Mammal::move() const
{
cout << "Mammal moves a step!" << endl;
}
void Mammal::speak() const
{
cout << "What does a mammal speak? Mammilian!" << endl;
}
Once you have completed class Mammal and Dog, build the following main program.
#include "Mammal.h"
#include "Dog.h"
int main ()
{
Mammal *pDog = new Dog;
pDog->move();
pDog->speak();
//Dog *pDog2 = new Dog;
//pDog2->move();
//pDog2->speak();
delete pDog;
//delete pDog2;
return 0;
}
What does it output, and is that what you expected? Remove the keyword virtual from the Mammal class and try it again. Now what happens? Next, put in another pointer to pDog2 in the main program, but this time make it a pointer to a Dog, not a Mammal and create a new Dog (as seen in code comments). Now what happens? What you should realize is that by making the method speak() virtual, we can have a bit different behavior through dynamic (runtime) binding.
-
Develop additional classes for Cat, Horse, and GuineaPig overriding the move() and speak() methods. (If you didn’t know, guinea pigs go “wheep wheepLinks to an external site.”). Make sure to also define a constructor and destructor for each of these classes, and that when you run your program, you can also see that the correct constructors and destructors are being called. Recall that a derived class will always call the parents constructors and destructors, so if you see this behavior, that is okay. Just make sure you are also calling the derived class’ constructors and destructors.
Test with the modified main:
int main ()
{
Mammal* theArray[5];
Mammal* ptr;
int choice;
for (int i = 0; i < 5; i++)
{
cout << "(1)dog (2)cat (3)horse (4)guinea pig: ";
cin >> choice;
switch (choice)
{
case 1: ptr = new Dog;
break;
case 2: ptr = new Cat;
break;
case 3: ptr = new Horse;
break;
case 4: ptr = new GuineaPig;
break;
default: ptr = new Mammal;
break;
}
theArray[i] = ptr;
}
// Iterate through array, and have each animal speak
for (int i = 0; i < 5; i++)
{
theArray[i]->speak();
}
// Always free dynamically allocated objects
for (int i = 0; i < 5; i++)
{
delete theArray[i];
}
return 0;
}
Sample run:
(1)dog (2)cat (3)horse (4)guinea pig: 1
Mammal constructor...
Dog constructor...
(1)dog (2)cat (3)horse (4)guinea pig: 2
Mammal constructor...
Cat constructor...
(1)dog (2)cat (3)horse (4)guinea pig: 3
Mammal constructor...
Horse constructor...
(1)dog (2)cat (3)horse (4)guinea pig: 4
Mammal constructor...
Guinea Pig constructor...
(1)dog (2)cat (3)horse (4)guinea pig: 5
Mammal constructor...
What does a dog say? Woof!
What does a cat say? Meow!
What does a horse say? Neigh!
What does a Guinea Pig say? Wheep WHEEP!
What does a mammal speak? Mammilian!
Dog destructor...
Mammal destructor...
Cat destructor...
Mammal destructor...
Horse destructor...
Mammal destructor...
Guinea Pig destructor...
Mammal destructor...
Mammal destructor...
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