method returning a pointer to a structure

Hi...
I am quite new to C++ (but no to programming or OOP) so, I have some questions specific to C++ syntax, etc ;) I hope you can help me as you did when I was trying to learn C ;)

I have a Class like: (I am using the C based openCV library)
(IplImage is a structure so I want to get returned a pointer to the structure created inside each method, This would have perfect sense in Objective-C)

Code:

---

#include "cv.h"
#include "highgui.h"
class CylindricalWarper{
        private:
        float fx,fy; //focal lenght
        float cx,cy; //optical center
        float k1,k2; //radial distorition coeficients
        public:
        void InitInstance(CString cameraString);
        IplImage * CorrectDistortion(IplImage *image);
        IplImage * CylindricalWarp(IplImage *undistorted);
};

---

And My questions are
1. Do I need a SuperClass? (ie: class CylindricalWarper:Warper{... )or is up to me?
and what is the most basic Class (which all objects inherit from) in C++

2. When I compile it I got two errors: error C2440: 'initializing' : cannot convert from 'void *' to 'IplImage *'
Each one in the first line inside CorrectDistortion method and CylindricalWarp method.
I think it is not just like C when you write something like

Code:

---

IplImage * correctDistortion(IplImage *);

---

What is the correct way?

3. What is the meaning and what is used for the word "virtual" ?

Any response would be very appreciated.
Regards
Ignacio.


PD: this task could be accomplished without classes but just for learning purposes I decided to make such a class

1. There is no C++ analogue to Object or whatever; there is no overarching base class that everything is a member of.

2. Are you asking whether you need a superclass (which is what you say) or a constructor (which is what you show)?

3. In C++ you must cast all your pointers explicitly from void * to whatever *; it doesn't happen automatically.

4. virtual means "this function might be overridden by an inheriting class, so check first".

pretty fast!,
Thanks.
to tabstop:
For 1 and 2, I meant when writting the definition of the class:
I don't need to specify what class is inheriting from? (I mean if is mandatory or not... it seems not to be mandatory right?)

I just got this part from a MFC project I am doing and as you see CAAboutDlg is inheriting from CDialog, that is why I asked if all the classes I make should have a parent?

Code:

---

class CAboutDlg : public CDialog
{
public:
        CAboutDlg();

// Dialog Data
        enum { IDD = IDD_ABOUTBOX };

        protected:
        virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support

// Implementation
protected:
        DECLARE_MESSAGE_MAP()
};

---

3 I just solved the error, sorry it was an opencv library usage mistake, so not regarding c++
4 thanks this is very clear now

There is no underlying "base" class that all classes must inherit from in C++ as tabstop said. In MFC, classes like CDialog are provided as "foundations" that allow the programmer to build upon them instead of working straight from the ground up, hence the inheritance.