创建不与虚拟基类一起使用的对象的克隆 [英] Creating clone of an object not working with virtual base class

问题描述

 ＃include< iostream> 
 using namespace std; 
 
类东西
 {
 public：
 int j; 
 Something（）：j（20）{cout<Something initialized。j =<< j<< endl;} 
}; 
 
 class Base 
 {
 private：
 Base（const Base&）{} 
 public：
 Base（）{} 
 virtual Base * clone（）{return new Base（* this）; } 
 virtual void ID（）{cout<<BASE<< endl; } 
}; 
 
类派生：public Base 
 {
 private：
 int id; 
 Something * s; 
 Derived（const Derived&）{} 
 public：
 Derived（）：id（10）{cout<<Called constructor and assigned id<< endl; s = new Something（）;} 
〜Derived（）{delete s;} 
 virtual Base * clone（）{return new Derived（* this）; } 
 virtual void ID（）{cout<<DERIVED id =<< id<< endl; } 
 void assignID（int i）{id = i;} 
}; 
 
 
 int main（）
 {
 Base * b = new Derived（）; 
 b-> ID（）; 
 Base * c = b-> clone（）; 
 c-> ID（）; 
} // main 
  

运行时：

 调用的构造函数和分配的ID 
初始化的东西。 j = 20 
 DERIVED id = 10 
 DERIVED id = 0 
  

与此，此和

在第一个链接中，Space_C0wb0y表示

因为克隆方法是
的方法，实际的对象的类，它可以
也创建一个深度副本，它可以访问
所有类的成员
to，所以没有问题。

我不明白深拷贝可能发生。在上面的程序中，甚至不发生浅拷贝。 我需要它来工作，即使Base类是一个抽象类。我如何在这里做一个深拷贝？帮助？

解决方案

好吧，你的复制构造函数什么也不做，所以你的克隆方法不会复制。 p>

查看行 Derived（const Derived&）{}

编辑：如果你添加代码来复制Derived的所有成员，它将变成浅拷贝。如果你也复制（通过制作一个新的实例）你的Something的实例，它将成为一个深层副本。

#include<iostream>
using namespace std;

class Something
{
  public:
  int j;
  Something():j(20) {cout<<"Something initialized. j="<<j<<endl;}
};

class Base
{
  private:
    Base(const Base&) {}
  public:
    Base() {}
    virtual Base *clone() { return new Base(*this); }
    virtual void ID() { cout<<"BASE"<<endl; }
};

class Derived : public Base
{
  private:
    int id;
    Something *s;
    Derived(const Derived&) {}
  public:
    Derived():id(10) {cout<<"Called constructor and allocated id"<<endl;s=new Something();}
    ~Derived() {delete s;}
    virtual Base *clone() { return new Derived(*this); }
    virtual void ID() { cout<<"DERIVED id="<<id<<endl; }
    void assignID(int i) {id=i;}
};


int main()
{
        Base* b=new Derived();
        b->ID();
        Base* c=b->clone();
        c->ID();
}//main

On running:

Called constructor and allocated id
Something initialized. j=20
DERIVED id=10
DERIVED id=0

My question is related to this, this and this post.

In the first link, Space_C0wb0y says

"Since the clone-method is a method of the actual class of the object, it can also create a deep-copy. It can access all members of the class it belongs to, so no problems there."

I don't understand how a deep copy can happen. In the program above, not even a shallow copy is happening. I need it to work even if the Base class is an abstract class. How can I do a deep copy here? Help please?

解决方案

Well, your copy constructor does nothing, so your clone method does nothing in the way of copying.

See line Derived(const Derived&) {}

EDIT: if you add code to copy by assignment all members of Derived, it will become a shallow copy. If you also copy (by making a new instance) your instance of Something, it will become a deep copy.

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