虚基类和多重继承总结

1，虚基类，其构造函数总是在最后一个层次最先并且真正被执行。

实例代码：

#include <iostream>
using namespace std;

class A
{
public:
    A(const string& s)
    {
        cout << "A " << s << endl;
    }
    virtual ~A() {}
};

class B
{
public:
    B(const string& s)
    {
        cout << "B " << s << endl;
    }
    virtual ~B() {}
};

class C
{
public:
    C(const string& s)
    {
        cout << "C " << s << endl;
    }
    virtual ~C() {}
};

class D
{
public:
    D(const string& s)
    {
        cout << "D " << s << endl;
    }
    virtual ~D() {}
};

class E : public A, virtual public B, virtual public C
{
public:
    E(const string& s) : A("from E"), B("from E"), C("from E")
    {
        cout << "E " << s << endl;
    }
};

class F : virtual public B, virtual public C, public D
{
public:
    F(const string& s) : B("from F"), C("from F"), D("from F")
    {
        cout << "F " << s << endl;
    }
};

class G : public E, public F
{
public:
    G(const string& s) : B("from G"), C("from G"), E("from G"),  F("from G")
    {
        cout << "G " << s << endl;
    }
};

int main()
{
    //虚基类的构造函数最先执行
    G g("from main");
}

输出：

引用

B from G

C from G

A from E

E from G

D from F

F from G

G from main

总结：虚基类构造函数最先被执行，然后按照从左到右，从上到下的顺序依次执行每一个构造函数。