Referencing derived class parameter from base class

Question

new to both managed c++ and stack overflow so I hope I'm doing this right.

I'm having a hard time finding a way to write a function with a base class parameter that requires a derived class's class variable.

My base class is called ImageBase and has two class variables: int rows, cols;

public ref class ImageBase
{
    public:
        int num_rows;
        int num_cols; 
}

Derived from that is an abstract, templated class called ImageT that only contains a templated 2-D array, pix:

template<class T> public ref class ImageT abstract : public ImageBase
{
public:
    property T** pix
    {
        public: T** get() { return rows; }
        protected: void set(T** val) { rows = val; }
    }
}

Derived from ImageT are RealImage, ShortImage and ComplexImage, which simply change the template type "T" to float, short or complex respectively. Here is a little MS Paint diagram of the class structure if this is easier to understand:

Class Hierarchy

My question is: if I were to write a very general function like:

void printPixels(ImageBase^ img)

so that I could pass it a RealImage, ComplexImage etc, how would I access the variable "pix" from an ImageBase type?

Answer 1

You cannot. At least not without tricks.

To solve this, I would recommend to templatize the printPixels() function:

template<class T> void printPixels(ImageT<T>^ img)

If you really need it, you could add a printPixels(ImageBase^ img) that checks the type of img, casts it, and calls the right printPixels(ImageT<T>^ img) for the real work.