派生类的构造函数显示调用虚基类的构造函数

      当调用派生类C的构造函数动态创建派生类对象时，只调用一次虚基类A的构造函数，\

而派生类C的直接基类B1，B2(同时也是A的派生类)对虚基类A的构造函数的调用将被忽略。

例子：

#include <iostream>
using namespace std;

class A
{
public:
A(int x)
{
a = x;
cout<<"A类构造函数"<<endl;
}
private:
int a;
};
class B1 : virtual public A //A是B1,B2的虚基类
{
public:
B1(int x, int y) : A(x)
{
b1 = y;
cout<<"B1类构造函数"<<endl;
}
private:
int b1;
};
class B2 : virtual public A //A是B1,B2的虚基类
{
public:
B2(int x, int y) : A(x)
{
b2 = y;
cout<<"B2类构造函数"<<endl;
}
private:
int b2;
};
class C : public B1, public B2 //B1,B2是C的直接基类,A是C的间接虚基类
{
public:
C(int x, int y, int z, int w) : B1(x,y),B2(x,z),A(x)
{
c = w;
cout<<"C类构造函数"<<endl;
}
private:
int c;
};
int main()
{
C *pc = new C(1,2,3,4);
delete pc;

return 0;
}

程序运行显示结果：