如下列代码所示的基类（base）及其派生类（derived），则生成一个派生类的对象时，只调用派生类的构造函数。
#include <iostream>
using namespace std;
class base {
public:
base() {
cout << "base constructor" << endl;
}
~base() {
cout << "base destructor" << endl;
}
};
class derived : public base {
public:
derived() {
cout << "derived constructor" << endl;
}
~derived() {
cout << "derived destructor" << endl;
}
};