指针到指针不支持 C++ 多态性

Question

我正在寻找一种正确的方法来清理我的指针。这里是示例代码:

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;
}

但是编译器报错:

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

Answer 1

正确处理内存的方法有很多。

接近您的示例的是:

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

此外，您可能想改用 std::auto_ptr。它看起来像:

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