已知Base类包含一个protected的整型变量x，同时包含一个public的print()函数；其他类没有数据成员。 根据下图将程序补充完整（主要是补充每个类的构造函数）。 程序运行结果： Base()... Base1()... x=1 Base()... Base2()... x=2 Base()... Base1()... Base2()... Derive()... x=3 请注意，main()函数或给定部分必须按如下所示编写： int main() { Base1 b1(1); b1.print(); Base2 b2(2); b2.print(); Derive d(3); d.print(); return 0; }

代码如下：

#include <iostream>
using namespace std;

class Base {
protected:
    int x;
public:
    Base() { cout << "Base()... "; }
    void print() { cout << "x=" << x << endl; }
};

class Base1 : virtual public Base {
public:
    Base1(int a) { x = a; cout << "Base1()... "; }
};

class Base2 : virtual public Base {
public:
    Base2(int a) { x = a; cout << "Base2()... "; }
};

class Derive : public Base1, public Base2 {
public:
    Derive(int a) : Base(), Base1(a), Base2(a) { cout << "Derive()... "; }
};

int main() {
    Base1 b1(1);
    b1.print();
    Base2 b2(2);
    b2.print();
    Derive d(3);
    d.print();
    return 0;
}

输出结果为：

Base()... Base1()... x=1
Base()... Base2()... x=2
Base()... Base1()... Base2()... Derive()... x=3