Question

class Base {
public:
    int a;
    Base():a(0) {}
    virtual ~Base();
}
class Derived : public Base {
public:
    int b;
    Derived():b(0) {
        Base* pBase = static_cast<Base*>(this);
        pBase->Base();
    }
    ~Derived();
}

Is the call to the base class constructor necessary or does c++ do this automatically? e.g.
Does C++ require you to initialize base class members from any derived class?

Answer 1

The base class’s constructor will automatically be called before the derived class’s constructor is called.

You can explicitly specify which base constructor to call (if it has multiple) using initialization lists:

class Base {
  public:
    int a;
    Base():a(0) {}
    Base(int a):a(a) {}
};
class Derived {
  public:
    int b;
    Derived():Base(),b(0) {}
    Derived(int a):Base(a),b(0) {}
};