Question

写出下列程序的运行结果，并说明原因.(c++)

class Base{
public:
Base(int x):d1(x){cout<< “Base cons.”<<endl;}
~Base(){cout<< “Base des.”<<endl;}
};
class Derived:public Base{
public:
Derived(int x):Base(x) {cout<< “Derived cons.”<<endl;}
~Derived(){cout<< “Derived des.”<<endl;}
};
void main()
{ Derived obj(5); }

Answer 1

你好，程序有错误，做如下修改：

#include <iostream>
using namespace std;
class Base{
public:
	int d1;
Base(int x):d1(x){cout<< "Base  cons."<<endl;}
~Base(){cout<< "Base  des."<<endl;}
};
class Derived:public Base{
  public:
Derived(int x):Base(x) {cout<< "Derived cons."<<endl;}
~Derived(){cout<< "Derived des."<<endl;}
};
void main()
{  Derived obj(5);  }

 运行结果如下：

Base  cons.

Derived cons.

Derived des.

Base  des.

原因：

先构建基类实例

再构建派生类实例

派生类实例析构

基类实例析构