C++封闭类的复制构造函数

原题：mooc北大的c++国家精品课​​http://cxsjsxmooc.openjudge.cn/2019t3summerall/011/​​

#include <iostream>
#include <string>
using namespace std;
class Base {
public:
  int k;
  Base(int n):k(n) { };
};
class Big
{
public:
  int v;
  Base b;
  Big(int init_n):b(init_n),v(init_n){         //构造函数
  }
  Big(const Big& init_c)             //这里这样定义复制构造函数是不对的
  {
    v=init_c.v;
    b=init_c.b;
  }
  
  
};
int main()
{
  int n;
  while(cin >>n) {
    Big a1(n);
    Big a2 = a1;
    cout << a1.v << "," << a1.b.k << endl;
    cout << a2.v << "," << a2.b.k << endl;
  }
}

错误如上，

正确代码如下：

#include <iostream>
#include <string>
using namespace std;
class Base {
public:
  int k;
  Base(int n):k(n) { };
};
class Big
{
public:
  int v;
  Base b;
  Big(int init_n):b(init_n),v(init_n){
  }
  Big(const Big& init_c):v(init_c.v),b(init_c.b)         //这样构造复制构造函数是正确的 
  {
  }
  
  
};
int main()
{
  int n;
  while(cin >>n) {
    Big a1(n);
    Big a2 = a1;
    cout << a1.v << "," << a1.b.k << endl;
    cout << a2.v << "," << a2.b.k << endl;
  }
}