Virtual inheritance constructor selection

Question

Why does this print 20000? Code explicitly calls specific base constructors all the way up the inheritance train, yet ignores specified constructor and uses the default constructor instead.

#include <iostream>

struct Car
{
  Car() : price(20000) {}
  Car(double b) : price(b*1.1) {}
  double price;
};

struct Toyota : public virtual Car
{
  Toyota(double b) : Car(b) {}
};

struct Prius : public Toyota
{
  Prius(double b) : Toyota(b)  {}
};

int main(int argc, char** argv)
{
  Prius p(30000);

  std::cout << p.price << std::endl;

  return 0;
}

Answer 1

Virtual base class must be constructed by the most-derived class; that's the only way that makes sense considering the possibility of a diamond-shaped hierarchy.

In your case, Prius constructs Car using its default constructor. If you want the other constructor, you'd have to call it explicitly, as in

Prius(double b) : Car(b), Toyota(b) {}