无法访问派生类中的受保护成员

Question

I have a setup something along the lines of this. Multiple levels of inheritance from a single base class containing a protected member x.

class Sprite {
protected:
    float x, y;
}

class AnimatedSprite : Sprite {
public:
    void draw(float x, float y);
}

class Player : AnimatedSprite {
public:
    void draw(float x, float y);
}

The implementation for the method draw in derived class Player is something along these lines.

void Player::draw(float x, float y) {
    AnimatedSprite::draw(this->x, this->y);
}

However compiler is complaining that members x and y are inaccessible, even though they are listed as protected in the base class.

Answer 1

Derivation for a class is private by default. If you want to access the protected base members, then you must make the derivation public :

class AnimatedSprite : public Sprite

// ...

class Player : public Sprite

(You could also make the derivation protected , but that would be a rather exotic thing to do. You could likewise make the first derivation public or protected and leave the second one private , but that would not match the supposed intention of the class hierarchy. public inheritance is clearly what you are looking for in both cases.)

Answer 2

AnimatedSprite uses private inheritance, so the members of Sprite become private members of AnimatedSprite . You might want to use protected inheritance:

class AnimatedSprite : protected Sprite {
public:
    void draw(float x, float y);
}

class Player : protected AnimatedSprite {
public:
    void draw(float x, float y);
}