Call virtual method immediately after construction

Question

I need to call a virtual method for all classes derived from a given base base class right after the construction of the derived object. But doing so in the base class constructor will result in a pure virtual method call

Here is a simplified example:

struct Loader {
    int get(int index) { return 0; }
};

struct Base{
    Base() {
        Loader l; 
        load( l ); // <-- pure virtual call!
    }
    virtual void load( Loader & ) = 0;
};

struct Derived: public Base {
    int value;
    void load( Loader &l ) {
        value = Loader.get(0);
    }
};

I can call load at the Derived constructor, but Derived could not know how to create a Loader. Any ideas/workarounds?

Answer 1

The problem is that base class construction occurs before the derived class is fully constructed. You should either call "load" from the derived class, initialise throguh a different virtual member function or create a helper function to do this:

Base* CreateDerived()
{
    Base* pRet = new Derived;
    pRet->Load();
    return pRet;
}