Inheritance and Constructors

[Aniviel833]

Hey all,

I'm having some problems with my constructors. I have a base class and an inherited class. How do constructors work in this situation?

I've tried writing a seperate constructor for my inherited class, but it wouldn't recognize any of the variables from the base class. (But functions in the inherited class would.) So then I created the same variables in the inherited class as I had in the base class. (Yeah, yeah... ) But, unsurprisingly, the constructor still doesn't work. Everything compiles fine, but if I try and create a new object of type MyInheritedClass, The object is created with the default constructor from the base class.
</stupidity>

So, if someone could point me towards a tutorial addressing this, or explain it, I'd appreciate it.

(Or shall I post the code? Is this a situation where it should work but I've written some really stupid code?)

Also, would someone recommend a new book to me? My 'Beginner' books don't address lots of things like this, (they minimally address classes, inheritance, and constructors, but don't really show how they work in many situations like this...) yet I'm still very much a noob.

Thanks!
-Stacy

[QUantumAnenome]

A class variable can be in the public:, protected:, or private: section.
Private data is not inherited. An inherited class can only see it's base class's public or protected members.

When an inherited class is created, it first calls the base class's constructor.

[fp_unit]

class 2dCoord
{
public:
    2dCoord(double x, double y) { x_ = x; y_ = y; }

protected:
    double x_;
    double y_;
};



class 3dCoord : public 2dCoord
{
public:
    3dCoord(double x, double y, double z) {
        // Call base-class constructor with x and y values
        2dCoord(x, y);
        z_ = z;
    }
    void print() const {
        cout << "x = " << x_ << "\ny = " << y_
             << "\nz = " << z_ << endl;
    }

protected:
    double z_;
};



int main()
{
    3dCoord t(489.2210, 5939.6667, 115.293);
    t.print();
}

That should output:

x = 489....
y = 5939.....
z = 115....

Notice the call to the base class constructor. Theres more efficient ways to do it but you should practice with simple inheritance first (like this) before getting into more advanced inheritance.

As for books, I have too many, but I like "C++ How to Program" by Deitel & Deitel, and "C++ Primer Plus" by Stephen Prata.

[redhead]

As for books, I have too many...

my thought exactly, altho I would say you can never have too many.. But if you look at my bookcase you'd might think theres way too many programming related ones.

[Aniviel833]

Sorry it's taken me so long to reply-- I've been busy these past few weeks getting ready for school.

Anyway, thank you for the explanation. I've got everything working in a simple example, though I may be back asking questions about my actual program. (There's no way it could be this easy, right? )

Thanks especially to fp_unit for the code, and book suggestions; both are most appreciated.

-Stacy

[Valmont]

Also keep in mind:
When you create an instance of a class, mind that this order is executed:

- base class constructors
- child class constructors

on destruction:

- child class destructors
- base class destructors

Anyway, just ask if you don't get it. My coding system should be up and running soon.