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sham · Apr 8th, 2005, 10:16 PM

How run time polymorphism is achieved in C++ ?

Cerulean · Apr 9th, 2005, 4:50 AM

Declare a member virtual in a class then subclass that class and re-implement that member. Here's an untested sample:

// A base class which has a virtual 'draw' method.
class Base {
    public:
        virtual void draw() {
            std::cout << "Base::draw()\n";
        }
};

// This class re-implements the draw method
class Sub : public Base {
    public:
        void draw() {
            std::cout << "Sub::draw()\n";
        }
};

Now lets say I have a function that takes a Base object pointer as a parameter and then calls draw on it:

(Toggle Plain Text)

void callDraw(Base *b) {
    b->draw();
}

I can create an instance of the subclass and pass a pointer to it to callDraw and it will call the subclasses draw method.

(Toggle Plain Text)

Sub *s = new Sub();
callDraw(s);      // Output: 'Sub::draw()'

Hope that's been helpful. If you need clarification on a certain point be more specific and i'll do my best.

java_roshan · Apr 11th, 2005, 10:51 AM

I wud just like to add.
In Run time polymorphism, the compiler does not know which function it has to select for a particular object if there are two functions with the same name and same prototypes. The selection of the function is done while the code is executed.

Apr 8th, 2005, 10:16 PM	#1
sham Newbie Join Date: Mar 2005 Posts: 29 Rep Power: 0	How run time polymorphism is achieved in C++ ? How run time polymorphism is achieved in C++ ?

Apr 9th, 2005, 4:50 AM	#2
Cerulean Professional Programmer Join Date: Apr 2005 Location: London, England Posts: 459 Rep Power: 4	Declare a member virtual in a class then subclass that class and re-implement that member. Here's an untested sample: (Toggle Plain Text) // A base class which has a virtual 'draw' method. class Base { public: virtual void draw() { std::cout << "Base::draw()\n"; } }; // This class re-implements the draw method class Sub : public Base { public: void draw() { std::cout << "Sub::draw()\n"; } }; // A base class which has a virtual 'draw' method. class Base { public: virtual void draw() { std::cout << "Base::draw()\n"; } }; // This class re-implements the draw method class Sub : public Base { public: void draw() { std::cout << "Sub::draw()\n"; } }; Now lets say I have a function that takes a Base object pointer as a parameter and then calls draw on it: (Toggle Plain Text) void callDraw(Base b) { b->draw(); } void callDraw(Base b) { b->draw(); } I can create an instance of the subclass and pass a pointer to it to callDraw and it will call the subclasses draw method. (Toggle Plain Text) Sub s = new Sub(); callDraw(s); // Output: 'Sub::draw()' Sub s = new Sub(); callDraw(s); // Output: 'Sub::draw()' Hope that's been helpful. If you need clarification on a certain point be more specific and i'll do my best.

Apr 11th, 2005, 10:51 AM	#3
java_roshan Professional Programmer Join Date: Mar 2005 Location: Student of University of Mumbai, Maharashtra State, India Posts: 344 Rep Power: 4	I wud just like to add. In Run time polymorphism, the compiler does not know which function it has to select for a particular object if there are two functions with the same name and same prototypes. The selection of the function is done while the code is executed. __________________ Visit: http://www.somaiya.edu

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