继承类中的子对象和基类对象的初始…

考察下面的程序：

class point1 
{
public:
 point1();
 point1(int i);
 virtual ~point1();
private:
  int x;  
};

point1::point1()
{
   x=1;
   cout<<"point1's default constructor called!\n";
}
point1::point1(int i)
{
 x=i;
    cout<<"point1's  constructor called!\n";
}
point1::~point1()
{

}

 

 

class point2 : public point1 
{
public:
 point2();
    point2(int i,int j,int k);
 virtual ~point2();
    point1 p;
};

point2::point2()
{
    cout<<"point2's defaule constructor called\n";
}
point2::point2(int i,int j,int k)
{
 cout<<"point2's constructor called\n";
}

point2::~point2()
{

}

 

 

//主函数

void main()
{
   point2 pp;
   point2 pp1(1,2,3);
}

运行结果

point1's default constructor called!
point1's default constructor called!
point2's defaule constructor called
point1's default constructor called!
point1's default constructor called!
point2's constructor called

 

 

如果函数

point2::point2(int i,int j,int k)
{
 cout<<"point2's constructor called\n";
}

改为：

point2::point2(int i,int j,int k):p(j)
{
 cout<<"point2's constructor called\n";
}

运行结果为：

point1's default constructor called!
point1's default constructor called!
point2's defaule constructor called
point1's default constructor called!
point1's  constructor called!
point2's constructor called

 

 

结论：

(1)派生类中的基类子对象和子对象必须初始化，初始化在派生类的构造函数的初始化列表中，如果初始化列表中没有进行初始化，则调用缺省的构造函数进行初始化。

(2)派生类构造函数的调用顺序：

   基类的构造函数

   子对象类的构造函数

   派生类的构造函数