Question

Why the following example prints ‘0’ and what must change for it to print ‘1’ as I expected ?

#include <iostream> struct base {    virtual const int value() const {       return 0;    }    base() {       std::cout << value() << std::endl;    }    virtual ~base() {} };  struct derived : public base {    virtual const int value() const {       return 1;    } };  int main(void) {    derived example; } 

Answer 1

Because base is constructed first and hasn’t ‘matured’ into a derived yet. It can’t call methods on an object when it can’t guarantee that the object is already properly initialized.