Here I give an example which can solidate your idea
how to use this const effectively.
The code looks like this:
#include
using namespace std;
class Shape{
public:
virtual void draw() =0;
virtual void draw() const =0;
};
class Rectangle:public Shape{
public:
virtual void draw() const;
virtual void draw();
};
void Rectangle::draw() const
{cout<<"This is const version of Rectangle.\n";};
void Rectangle::draw()
{cout<<"This is normal version of Rectangle.\n";};
void main()
{
Shape* sp=new Rectangle;
sp->draw();
const Shape* sp1=new Rectangle;
sp1->draw();
Shape* const sp2=new Rectangle;
sp2->draw();
const Shape* const sp3=new Rectangle;
sp3->draw();
}
Can you guess the result of this program? If you
are not 100% certain about your answer, please
copy this program into your editor and compile and
run it. You will get the perfect sense about how
to use the const!
As a reminder, you should notice the code:
Shape* sp=new Rectangle;
If you are writing the codes like:
Shape *sp;
sp->draw();
You will find it can not compile as Shape itself
is abstract class.
Not so fancy? Try to define a pure virtual function by adding:
void Shape::draw() const
{ cout<<"This is const version of Shape.\n";
};
void Shape::draw()
{ cout<<"This is normal version of Shape.\n";
};
void Rectangle::draw() const
{ Shape::draw();
cout<<"This is also const version of Rectangle.\n";
};
void Rectangle::draw()
{ Shape::draw();
cout<<"This is also normal version of Rectangle.\n";
};
run the codes again...
