派生C ++类如何通过基指针来克隆本身？ [英] How can a derived C++ class clone itself via a base pointer?

问题描述

这是我想要做的（这段代码不工作）：

  class Base 
 {
 virtual Base * clone（）{return new Base（this）; } 
 virtual void ID（）{printf（BASE）; 
}; 
 
 class Derived：publc Base 
 {
 virtual Base * clone（）{return new Derived（this）; } 
 virtual void ID（）{printf（DERIVED）; } 
} 
 
。 
。 
派生d; 
 Base * bp =& d; 
 Base * bp2 = bp-> clone（）; 
 
 bp2-> ID（）; 
  

我会像是看到DERIVED打印出来。我得到的是BASE。我是一个长期的C程序员，相当有经验的C ++ ...但我没有任何进展与这一个...任何帮助将不胜感激。

解决方案

一旦所有的编译错误都修复了，我最终得到：

  #include< cstdio> 
 
 class Base 
 {
 public：
 Base（）{} 
 Base（const Base&）{} 
 virtual Base * clone （）{return new Base（* this）; } 
 virtual void ID（）{printf（BASE）; } 
}; 
 
 class Derived：public Base 
 {
 public：
 Derived（）{} 
 Derived（const Derived&）{} 
 virtual Base * clone（）{return new Derived（* this）; } 
 virtual void ID（）{printf（DERIVED）; } 
}; 
 
 
 int main（）
 {
 Derived d; 
 Base * bp =& d; 
 Base * bp2 = bp-> clone（）; 
 
 bp2-> ID（）; 
} 
  

这就给你你想要的 - DERIVED。

Here's what I'm trying to do (this code doesn't work):

class Base
{
    virtual Base *clone() { return new Base(this); }
    virtual void ID() { printf("BASE");
};

class Derived : publc Base
{
    virtual Base *clone() { return new Derived(this); }
    virtual void ID() { printf("DERIVED"); }
}

.
.
Derived d;
Base *bp = &d;
Base *bp2 = bp->clone();

bp2->ID();

What I'd like is to see "DERIVED" printed out... what I get is "BASE". I'm a long-time C programmer, and fairly experienced with C++... but I'm not making any headway with this one... any help would be appreciated.

解决方案

Once all the compile errors are fixed, I ended up with this:

#include <cstdio>

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

class Derived : public Base
{
  public:
    Derived() {}
    Derived(const Derived&) {}
    virtual Base *clone() { return new Derived(*this); }
    virtual void ID() { printf("DERIVED"); }
};


int main()
{
  Derived d;
  Base *bp = &d;
  Base *bp2 = bp->clone();

  bp2->ID();
}

Which gives you what you are looking for -- DERIVED.

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