Thread: pointers and classes

Hello,

I am testing some code. I have a mammal class that has a virtual function Speak. I have 4 derived classes that inherit from the mammal class. The derived classes each have a Speak function.

Howevever, I am using the code below. And one thing I don't understand is this line.

Many thanks for any explanations for this line.

Code:

    //A mammal pointer that points to 4 mammal objects
    Mammal *animalArray = new Mammal[4];

    Mammal *animal;
    animal = new Dog;

    animalArray = animal; //Don't understand, shouldn't it be animalArray[0] = animal
    animalArray->Speak();

And I'm guessing, based on inherited classes, that what you want is an array of pointers-to-Mammal? If you try to copy a Dog object into a Mammal object slot, you'll lose stuff; but a pointer-to-Mammal can hold a pointer-to-Dog.

Originally Posted by execute

I believe you can also do:

*animalArray[0] = animal;

You could, but again you would lose anything "extra" in Dog that's not in Mammal (a la type slicing). This means that the presumed polymorphic call on the next line will fail.

Hello,

Thanks for all the response.

I think where I was really getting confused was this line here.

Code:

Mammal *animalArray = new Mammal[4];

I look at this line as: I am creating a single mammal pointer. That pointers to an array of mammal objects. Just want to check that my terminology is correct

Thanks,

Besides the leak, you are also very nearly treating an array as having polymorphic elements, and that isn't going to work.

Soma