关于父类的构造的顺序

1，没有虚基类的情况:

#include <iostream>
#include <cstdio>
using namespace std;

class A
{
public:
    A()
    {
        cout << "A" << endl;
    };
};

class B : public A
{
public:
    B()
    {
        cout << "B" << endl;
    };
};

class C : public A
{
public:
    C()
    {
        cout << "C" << endl;
    };
};

class D : public B, C
{
public:
    D()
    {
        cout << "D" << endl;
    };
};

int main()
{
    B b; //输出: A B 先构造基类,再构造子类
    D d; //输出: A B A C D
    return 0;
}

(2)虚基类的情况:

#include <iostream>
#include <cstdio>
using namespace std;

class A
{
public:
    A()
    {
        cout << "A" << endl;
    };
};

class VB : virtual public A
{
public:
    VB()
    {
        cout << "VB" << endl;
    };
};

class VC : virtual public A
{
public:
    VC()
    {
        cout << "VC" << endl;
    };
};

class VD : public VB, VC
{
public:
    VD()
    {
        cout << "VD" << endl;
    };
};


int main()
{
    VD vd; //输出: A VB VC VD
    //虚基类的subobject总是在最深的地方最先被构造
    return 0;
}