Why I get the error: "there is more than one default constructor"?

Question

I get the message:

Severity Code Description Project File Line Suppression State Error (active) E0339 class "D" has more than one default constructor)

and:

Severity Code Description Project File Line Suppression State Error C2668 'D::D': ambiguous call to overloaded function)

The error occurs in line marked with //(2)

if I remove line marked with //(1) the I can build my code.

class C {
    int i, j;

public:
    C(int x, int y) : i(x), j(y)
    {
        cout << "Konstr C" << endl;
    }
    C() : i(0), j(0)
    {
        cout << "Std-Konstr C" << endl;
    }
        ~C()
    {
        cout << "Destruktor C" << endl;
    }
};
class D : public C {
    int k, a, b;
    C c;
public:

    D():c(){ cout << "Std-Konstr D" << endl; }// (1)

    D(int x = 1) :c(x, 1), a(x), b(0), k(19)

    {
        cout << "Konstr-1 D" << endl;
    }
    D(int x, int y, int z) :C(x, y), a(1), b(2), c(x, y), k(z)
    {
        cout << "Konstr-2 D" << endl;
    }
    ~D()
    {
        cout << "Destruktor D" << endl;
    }
};
class E : public D {
    int m;
    C c;
    D b;
public:
    E(int x, int y) : c(2, 3), b(y), m(x + y)// (2)
    {
        cout << "Konstr E" << endl;
    }
    ~E()
    {
        cout << "Destruktor E" << endl;
    }
};

Answer 1

As the error message states, D() is ambiguous. The compiler has no way pf knowing if you meant to call the no-arg constructor, or the int constructor with a default value of 1.

One way to clear this ambiguity is to remove the default value of the x parameter:

D():c(){ cout << "Std-Konstr D" << endl; }// (1)

D(int x) :c(x, 1), a(x), b(0), k(19)
//    ^-- x=1 was removed here
{
    cout << "Konstr-1 D" << endl;
}