C ++多级继承-调用基本构造函数错误

Question

So I have a fairly complex programm that I dont whant to go into right now. I will include a toy example of the same process and then go over it in more detail.

In my Programm I encounter the Error constructor for 'Hunter' must explicitly initialize the base class 'WorldObject' which does not have a default constructor with multilevel inheritance: WorldObject -> Creature -> Hunter .

To recreate the same structure I made the following:

class Base
{
protected:
    int a;
public:
    Base(int a): a(a) { print("Base contructed"); }
    ~Base() { print("Base destroyed"); }
    virtual void printData() = 0;
};



class Derived1 : public Base
{
protected:
    int b;
public:
    Derived1(int a, int b): b(b), Base(a) { print("Derived1 contructed"); }
    ~Derived1() { print("Derived1 destroyed"); }
};


class Derived2 : public Derived1
{
protected:
    int c;
public:
    Derived2(int a, int b, int c) : c(c), Derived1(a, b) { print("Derived2 contructed"); }
    ~Derived2() { print("Derived2 destroyed"); }
    virtual void printData(){ //... }
}; 

Here, the constructor of Derived2 class created Derived1 via the initializer list and this in turn constructs Base "indirectly". This works like I expected.

However, in my complex Code, the Hunter class needs to explicitly call the WorldObject constructor. This looks like:

Hunter(sf::Texture &texture, float x, float y, sf::Font& font) : 
        WorldObject(texture,x, y, font),
        Creature(texture, x, y, font)
    { //... }

Here, The Creature constructor just passes every argument to the WorldObject constructor. WorldObject only has this constructor:

WorldObject(sf::Texture& texture, float x, float y, sf::Font& font) : m_sprite(texture)
{ //... }

and the used Creature constructor looks like this:

    Creature(sf::Texture &texture, float x, float y, sf::Font& font) : 
    WorldObject(texture, x, y, font), 
    NN(n_input_units, n_hidden_units, n_output_units)
{ //... }

Why do I need to initialize both WorldObject and Creature directly in my Programm, but in the toy example it works without the explicit Base constructor?

(( The pre-compiler is also complaining that there is no default constructor for WorldObject, and on compiling the above error appears))

Answer 1

I guess that in your complex code, Hunter directly inherits from WorldObject and not indirectly via Creature . If Creature inherits WorldObject , it will never be necessary for Hunter to pass any parameters to WorldObject .