Solved

# c++ polymorphism function

Posted on 2006-11-30
193 Views
Last Modified: 2010-04-01
Hello, I found the following code from one of the experts here, but I don't understand a lot of it.  Could someone please help me understand what the program is doing?  I understand the basics, but need help with understanding these lines.  I am not sure what teh ~ means.  Please help me understand.

class Shape
{
public:
Shape() {};
virtual ~Shape() {};
virtual void DrawShape() = 0;
};

class Circle : public Shape
{
public:
Circle() {};
virtual ~Circle() {};
virtual void DrawShape() { cout << "This is a circle" << endl; }
};

-----------------------------------------------
Here's the code someone wrote:
-----------------------------------------------
#include <iostream>

using namespace std;

class Shape
{
public:
Shape() {};
virtual ~Shape() {};
virtual void DrawShape() = 0;
};

class Circle : public Shape
{
public:
Circle() {};
virtual ~Circle() {};
virtual void DrawShape() { cout << "This is a circle" << endl; }
};

class Triangle : public Shape
{
public:
Triangle() {};
virtual ~Triangle() {};
virtual void DrawShape() { cout << "This is a triangle" << endl; }
};

class Rectangle : public Shape
{
public:
Rectangle() {};
virtual ~Rectangle() {};
virtual void DrawShape() { cout << "This is a rectangle" << endl; }
};

int main()
{
Shape* pShape = 0;
int ask = 0;
cout <<"=============================================="<<endl;
cout << "Do you want to display (type 1,2,or 3):" <<endl;
cout << "1. Circle"                                             <<endl;
cout << "2. Triangle"                                   <<endl;
cout << "3. Rectangle"                                             <<endl;
cout <<"----------------------------------------------"<<endl;
cin >> ask;
cin.get();

switch (ask)
{
case 1:
pShape = new Circle;
break;
cin.get();
case 2:
pShape = new Triangle;
break;
cin.get();
case 3:
pShape = new Rectangle;
break;
cin.get();
default:
cout << "Invalid choice.  Good-bye!" << endl;
cin.get();
return -1;

}
pShape->DrawShape();
delete pShape;
cin.get();

return 0;
}
0
Question by:meaar
• 2
3 Comments

LVL 45

Accepted Solution

sunnycoder earned 500 total points
ID: 18051859
Hi meaar,

~<functionName>
Where functionName is same as class name signifies destructor ...

Class Shape has 3 members ... a constructor which is empty and does nothing ...
A virtual destructor .... why we need a virtual destructor
http://blogs.msdn.com/oldnewthing/archive/2004/05/07/127826.aspx
http://www.codersource.net/cpp_virtual_destructors.html

And third member is a pure virtual function DrawShape() .. Note the =0. Pure virtual function is one whose implementation is mandatory for every class that derives from Shape class ...

Class Circle derives from Shape ... again an empty constructor and a virtual destructor ...
Since it derives from Shape, it provides an implementation for DrawShape - the pure virtual function in parent class ..

Now if you have
Shape * ptr;
Circle obj1;

ptr = &obj1;
ptr->DrawShape(); //this call will print "this is a circle"

Cheers!
sunnycoder
0

Author Comment

ID: 18051874
sunnycoder, your answer was nice you had to send it twice. :)
0

LVL 45

Expert Comment

ID: 18051974
:) ...

It reported failure on first attempt which as I discovered later was successful.

Deleted the duplicate post.

sunnycoder
Page Editor
0

## Join & Write a Comment Already a member? Login.

When writing generic code, using template meta-programming techniques, it is sometimes useful to know if a type is convertible to another type. A good example of when this might be is if you are writing diagnostic instrumentation for code to generat…
Container Orchestration platforms empower organizations to scale their apps at an exceptional rate. This is the reason numerous innovation-driven companies are moving apps to an appropriated datacenter wide platform that empowers them to scale at a …
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

#### 746 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

#### Need Help in Real-Time?

Connect with top rated Experts

8 Experts available now in Live!