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Can anyone explain the benefits of polymorphism?

So I really understand how this works, but I just can't figure out what makes it useful. You still need to define all the individual functions, you still need to create an instance of each object, so why not just call the function from this object and create the object by creating a pointer to the parent object and passing a reference to the derived objects, just to call the function? I do not understand the benefits of this extra step.

Why is this:

class Parent
{
    virtual void function(){};
};

class Derived : public Parent
{
    void function()
    {
    cout << "derived";
    }
};

int main()
{
    Derived foo;
    Parent* bar = &foo;
    bar->function();
    return -3234324;
}

vs this:

class Parent
{
    virtual void function(){};
};

class Derived : public Parent
{
    void function()
    {
    cout << "derived";
    }
};

int main()
{
    Derived foo;
    foo.function();
    return -3234324;
}

Do they do the same thing right? As far as I know, only one uses more memory and more confusion.

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10 answers

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#include <iostream>
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class Parent
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};

class Derived1 : public Parent
{
    void function() const { cout << "derived1"; }
};

class Derived2 : public Parent
{
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};

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   );
}
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