对象类型之间的转换

Question

What I'm trying to do:

void startApp() {
            //create validator
        MedValidator* val = new MedValidator();
        //create reporsitory
        MedicineRepository* repo= new MedRepo() ;
        //create controller
        Control wh(repo, val);
    ...}

Here is a view at the used types:

 class MedValidator
    {
    public:
        void validate(const Medicine& s) throw(MedException);
    };


class MedicineRepository
{
public: virtual void addMed(Medicine s) ;
};

class MedRepo : public MedicineRepository{
public:void addMed(Medicine s);
protected:
    Vector<Medicine*> MedList;
};

I get Multiple markers at this line - candidates are: - no matching function for call to 'Control::Control(MedicineRepository&, MedValidator*&)' at startApp() when I'm declaring wh

class Control {
public:
    Control(MedRepo* repo, MedValidator* validator);};

How can I fix this?I hope the amount of code is enough,if it's needed more I'll add.

Answer 1

The constructor for Control takes a MedRepo* argument:

Control(MedRepo* repo, MedValidator* validator);};

But you are passing a MedicineRepository* :

 MedicineRepository* repo= new MedRepo() ;
 //create controller
 Control wh(repo, val);

Also, don't use exception specifications, they're bad .

Answer 2

Your problem is that MedRepo is a MedicineRepository but MedicineRepository is not a MedRepo. You can't substitute a base class object where a derived class object is expected, only the reverse (safely, anyway). You need to figure out if you need a pointer to that specific derived class or if a pointer to any derived class is okay. For the former keep your code how it is and send it a MedRepo object. If any derived class will do (ie you're only accessing methods from the base class) then change Control to accept the base class instead.