Mammals don't fly

Bats are exceptions, they fly

Code Understanding

class Mammal {
public: virtual void fly(){cout<<“Mammals don’t fly”<<endl;} };
The fly() function in parent class Mammal is virtual as it is expected to be overridden in its child class.

class Bat:public Mammal { public: void fly(){cout<<“Bats are exceptions, they fly”<<endl;}};
The fly() function in this derived class is an overridden function and is called when object from Bat is in use

void Doesfly(Mammal *m) { m->fly();}
Since the object of Parent Mammal and Child Bat are type compatible so the passed parameter can be reference of object of Parent or of Child. When Parent object is passed function from parent is called, if object of child is passed function from child is called. This is basically a function that is following the dynamic or runtime polymorphism model.

int main() {
Bat b; Mammal m;
Objects of child class Bat and parent class Mammal are declared.

Doesfly(&m);  
This function is called with reference address of the parent object.

Doesfly(&b);
This function is called with reference address of the child object.

Note: This is a decent implementation of polymorphism in C++ as here function is same, parameter type is same but on the basis of from where the parameter originates at runtime the code portion to be called is changed.

return 0;}

Notes

• Dynamic polymorphism is also called runtime polymorphism as the decision of which path a action will take is decided at the runtime. This means that based on input condition it reaches a certain reference point which is not fixed at the time of compilation.
• Some people also classify this type of polymorphism as of class subtype based polymorphism. A good article with more examples is here
  http://www.catonmat.net/blog/cpp-polymorphism/
• You can also read the polymorphism concept article here.

Common Errors

• Care needs to be taken in referencing the pointer variables while passing as parameter in the function definition part and as addressof of an object type while calling the function.

Suggested Filename(s): dyn-poly.cpp,dynamic-polymorphism.cpp