c++ [钻石配置] 如何用继承初始化？

Question

I apologize if my question is dumb but i'm a beginner in c++. I'm working on diamond inheritance and i would like to know if it is possible to choose the specific parent class which will initilize an attribute for the child class.

To sum up, i would like this code to output B

Thank you for your answers !

PS: i'm working with c++98

#include <iostream>

class A
{
    protected:
        char    m_char;
    public:
        A(): m_char('A'){};
        char    getChar(){return m_char;};
        ~A(){};
};

class B : virtual public A
{
    private:
        
    public:
        B() {m_char = 'B';};
        ~B(){};
};

class C : virtual public A
{
    private:
        
    public:
        C() {m_char = 'C';};
        ~C(){};
};

class D : public B, public C
{
    private:
        
    public:
        D() {m_char = B::m_char;};
        ~D(){};
};

int main(void)
{
    D   d;
    std::cout << d.getChar() << std::endl;
}

Answer 1

Virtual base classes are initialized In depth-first, left-to-right order. So you would need to name B second in your inheritance for D to call its constructor last and thus setting the variable to B at the end.

class D : public C, public B

Answer 2

m_char = B::m_char; is self assignment (there is only one m_char ).

In virtual inheritance, it is the most derived class which initialize the virtual class (body does assignment).

How about being explicit in construction:

#include <iostream>

class A
{
protected:
    char m_char;
public:
    A() : m_char('A') {}
    char getChar() const { return m_char; }
    virtual ~A() {}
};

class B : virtual public A
{
public:
    B() : A('B') {}
};

class C : virtual public A
{
public:
    C() : A('C') {}
};

class D : public B, public C
{
public:
    D() : A('B'), B(), C() {}
};

int main()
{
    D d;
    std::cout << d.getChar() << std::endl;
}