Error when trying to define object of class type that is derived from an abstract class

Question

class Road {
private:
    std::vector<Vehicle*> container;
public:
    std::vector<Vehicle*> getContainer(){
        return container;
    }
    virtual void operator+(Vehicle *vehicle)=0;
};


class Highway: public Road {
public:
    virtual void operator+(Vehicle *vehicle) {
         getContainer().push_back(vehicle);
     }
};

Why do I get an error that I cannot allocate an object of abstract type when all of my virtual functions are overriden? It happens when I try to call Road r = Highway(); in my main class.

Answer 1

For Road r = Highway();, Road r means you're trying to define an object of type Road, which is an abstract class then the definition is not allowed. The initializer list part (i.e. = Highway()) doesn't affect the type of r, it just means r is slicing-copy initialized from an temporary object of type Highway.

You should use pointers/smart pointers or references with abstract class type, e.g.

Road* r = new Highway;
// using r ...
delete r;

or

Highway h;
Road& r = h;
// using r ...