指针到指针不支持C ++多态 [英] C++ polymorphism not supported for pointer-to-pointer

问题描述

我正在寻找一种正确的方法来清理指针。
这里的示例代码：

I'm searching for a proper way to clean my pointers. Here the example code:

class Parent {
   protected:
      int m_Var;
   public:
      Parent() : m_Var(0) {}
      virtual ~Parent() {}
      void PubFunc();
};

class Child : public Parent {
   protected:
      bool m_Bool;
   public:
      Child() : m_Bool(false) {}
      virtual ~Child() {}
      void ChildFunc();
};

void RemoveObj(Parent **ppObj)
{
   *ppObj->PubFunc();
   delete *ppObj;
   ppObj = NULL;
}

int main()
{
   Parent* pPObj = NULL;
   Child*  pCObj = NULL;
   pPObj = new Parent();
   pCObj = new Child();

   RemoveObj(&pPObj);
   RemoveObj(&pCObj); // This is line 33
   return 1;
}

但是编译器给出错误：

classes.cpp:33: error: invalid conversion from ‘Child**’ to ‘Parent**’
classes.cpp:33: error:   initializing argument 1 of ‘void RemoveObj(Parent**)’

推荐答案

有很多方法来正确处理内存。

There are soo many ways to handle memory correctly.

接近您范例的方法是：

template <typename T>
RemoveObj(T **p)
{
    if (p == NULL) return;
    delete *p;
    *p = NULL;
}

此外，您可能想使用std :: auto_ptr。它看起来像：

Additionally you might want to use std::auto_ptr instead. It would look like:

int main()
{
   std::auto_ptr<Parent*> pPObj(new Parent);
   std::auto_ptr<Child*> pCObj(new Child);
   // no deletes needed anymore

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