派生クラスが複数の基本クラスを直接継承

#include < iostream >
using namespace std;

class B1 {
public:
    B1() { cout << "B1 constructor call \n"; }
    ~B1() { cout << "B1 destructor call \n"; }
};

class B2 {
    int b;
public:
    B2() { cout << "B2 contructor call \n"; }
    ~B2() { cout << "B2 destructor call \n"; }
};


class D : public B1, public B2{
public:
    D() { cout << "call D constructor\n"; }
    ~D() { cout << "call D destructor\n"; }
};

int main()
{
    D ob;
    
    return 0;
}