How do I create an array of inherited class objects?

Question

I'm having a bit of trouble working on my current project. The project consists of taking lines of data from a file and creating an array of class objects that all inherit a base class.

So, this is what I understand so far:

class BaseClass {
    // create empty and non-empty constructor
}

class SubClass : public BaseClass {
    // create constructor specifically for this class 
}

int main() {
    BaseClass *array[size];
    array[index] = new SubClass();

    return 0;
}

Since the SubClass inherits the BaseClass, When I add a new object to the array it should be of type SubClass, correct?

When I debug the program and look at that object, it doesn't allow me to point to any of the SubClass methods/variables for manipulation which is what I need to be able to do.

Now when I was searching for answers I came across static casting, so I tried it to the extent of:

(static_cast<SubClass*>(array[index])->subclass_variable) = some_value

But that doesn't seem to work either, any help with this would be greatly appreciated.

How to create an array of inherited class objects in which I can access and manipulate individually. — Mark Wilcoxen
– Mark Wilcoxen, Commented Jan 28, 2017 at 17:20

lorro · Accepted Answer · 2017-01-28 17:23:11Z

2

One way to handle this is defining an interface (virtual methods) in the base class and implementation in SubClass:

class BaseClass {
    // create empty and non-empty constructor
    virtual void f() = 0;
}

class SubClass : public BaseClass {
    // create constructor specifically for this class 
    virtual void f() { std::cout << "I am your SubClass" << std::endl; }
}

Then you can call array[index]->f();.

Another way is visiting / type switching on the class, another is NVI, but those are somewhat more advanced topics.

answered Jan 28, 2017 at 17:23

lorro

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1 Comment

Mark Wilcoxen Over a year ago

Thank you so much! That solved it and now its running perfectly, you are the man!

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