Reply #8: Not quite... [View All]

[regnaD kciN]

The example you mentioned actually refers to operator overloading, not polymorphism.

Polymorphism refers to the use of virtual functions in classes derived from a master class.

Example: You have a base class titled Class1. You derive two new classes, titled Class2 and Class3, from it. Each of the three classes has a function titled Update().

You declare an array of pointers to Class1 objects, titled pClass[]. The thing is, some of the objects whose pointers you add to the array are Class2 and Class3 objects. (Since they're derived from Class1, you can do this.) Now, you create a loop like this:

for (int x = 0; x < ARRAY_SIZE; x++)
{
pClass(x)->Update();
// those should be square brackets around the x, but the forum software won't accept it!
}

What's going to get called?

If, when creating the base class, you declare Update() as a standard function, that loop will call the Class1's Update() function for each element in the array. If, however, you declare Update() a virtual function (i.e., you implement polymorphism), when the pointer is actually to a Class2 object, it will call Class2's Update() function instead. Same with Class3. The only time Class1's Update() function will be called is when the object itself is an instance of Class1, not Class2 or Class3.

(The previous time I was looking for work, when I had less experience with C++ than I do now, the above was a question in a phone interview I had with Microsoft. I didn't get it right, and wound up not being considered for the job because of it -- therefore, I made a point of memorizing it from then on. ;-) )