Inheritance and constructor problem

[Stefan Istrate]

I have the following code:

#include <iostream>
using namespace std;

class B {
int x;
public: B(int i) {x = i;}
};

class D1: virtual B {
public: D1(int i): B(i){}
};

class D2: virtual B {
public: D2(int i): B(i){}
};

class D3: B {
public: D3(int i): B(i){}
};

class D4: private B {
public: D4(int i): B(i){}
};

class D5: virtual public B {
public: D5(int i): B(i){}
};

class M1: D1, public D2, D3, private D4, virtual D5 {
public:
M1(): D5(5), D1(1), D2(2), D3(3), D4(4) {}
};

int main() {
M1 x;
}

This doesn't work and I don't know why. It seems that a constructor of
class B is called without parameters, but I can't figure where. Any
suggestions would be appreciated.

Thank you,
Stefan Istrate