Need help to understand Singleton class functionality

[shailesh kumar]

I have written code to understand the functionality of Singletom Class, by defintion -- singleton is one instance of a class and user of singleton doesn't have possibility to create another one. However, in my code I am able to create two instances of a Class. I would appreciate, if you can help me understand the basic concept through my code. Thank you very much..

class Rectangle
{
private:
int width, height;
static Rectangle* rectangle;
static bool instance_flag;
Rectangle(){}
~Rectangle(){}

public:
static Rectangle* getInstance();
int rectArea(void);
};

bool Rectangle::instance_flag = false;
Rectangle* Rectangle::rectangle = NULL;

Rectangle* Rectangle::getInstance()
{
if (!instance_flag)
{
rectangle = new Rectangle();
instance_flag= true;
return rectangle;
}
else return rectangle;

}

int Rectangle::rectArea()
{
width = 5, height = 10;
return width * height;
}


void main(void)
{
Rectangle *sc1 = Rectangle::getInstance();//one instance
Rectangle *sc2 = Rectangle::getInstance();//second instance

cout << "Rectangle Area is :" << sc1->rectArea() << endl;
cout << "Rectangle Area is :" << sc2->rectArea() << endl;
}

[AbstractionAnon]

You've not created two instances. You've created two pointers that point to the same (singleton) instance.

Add the following two lines to confirm that both pointers point to the same thing.

	cout << "@sc1= " << sc1 << endl;
	cout << "@sc2= " << sc2 << endl;

PLEASE USE CODE TAGS (the <> formatting button) when posting code.
It makes it easier to read your code and also easier to respond to your post.
http://www.cplusplus.com/articles/jEywvCM9/

[shailesh kumar]

Thanks AbstractionAnon.. I got it.. Sorry about not following the format while posting the code. Best Regards