Question

I have a problem with calling an inherited method. Probably I miss some virtual, const or & but I cannot find where

I have a base class Classifier with one “real” and one virtual function, the “real” function calls the virtual one. The child class MyClassifier defines the virtual inherited methon. Now when I call the “real” class on the MyClassifier object, I get compiler error.

class Classifier {
    public:
    bool classify(const Image& ii) 
    { 
        return classify(ii, ii.getRect()); 
    }

    virtual bool classify(const Image& ii, const rect_t& rect) const = 0;
};

class MyClassifier : public Classifier {
    public:
    bool classify(const Image& ii, const rect_t& rect) const;
};

bool
MyClassifier::classify(const Image& ii, const rect_t& rect) const
{
    // do stuff...
}

The calling code is:

// main...
MyClassifier c;
Image some_image;

c.classify(some_image);

And the error:

error: no matching function for call to ‘MyClassifier::classify(const Image&) const’
note: candidate is:
note: virtual bool MyClassifier::classify(const Image&, const rect_t&) const
note:   candidate expects 2 arguments, 1 provided

Answer 1

The overloaded method in the subclass hides the method from the base-class. You can fix it with a using-declaration:

class MyClassifier : public Classifier {
public:
    using Classifier::classify;
    bool classify(const Image& ii, const rect_t& rect) const;
};