Inheriting constructors

Question

Why does this code:

class A
{
    public: 
        explicit A(int x) {}
};

class B: public A
{
};

int main(void)
{
    B *b = new B(5);
    delete b;
}
         


        

Answer 1

This is straight from Bjarne Stroustrup's page:

If you so choose, you can still shoot yourself in the foot by inheriting constructors in a derived class in which you define new member variables needing initialization:

struct B1 {
    B1(int) { }
};

struct D1 : B1 {
    using B1::B1; // implicitly declares D1(int)
    int x;
};

void test()
{
    D1 d(6);    // Oops: d.x is not initialized
    D1 e;       // error: D1 has no default constructor
}