C++ 11:我可以显式调用基类析构函数来销毁派生类吗？

Question

我正在用C++ 11实现一个内存池.存储在内存池中的所有对象都需要从MemoryPoolObject类继承,但它们可能使用多重继承.

当我分配一个新对象时,我使用malloc来创建它,然后使用placement构造函数 - 我可以做,因为我知道它的类型(allocate()是一个模板函数,它将类型作为模板参数).我还将其大小存储在其上的对象上(作为MemoryPoolObject类的成员变量).

当我释放对象时,我想调用它的析构函数.但我不再知道对象类型.我知道它派生自MemoryPoolObject,它有一个虚拟析构函数.所以...如果我对~MemoryPoolObject()进行显式调用,那么它会做正确的事情(包括调用任何多重继承的基类的析构函数)吗？

这是一些代码.它没有显示如何在池中存储和检索未使用的对象.但这与手头的问题无关.

class BaseClass
{
public:
    virtual ~BaseClass();
    ...
};

class MemoryPoolObject
{
public:
    virtual ~MemoryPoolObject();

    // In reality I don't just expose this, but for simplicity...
    size_t m_ObjectSize;
};

class ChildClass : public BaseClass, public MemoryPoolObject
{
    virtual ~ChildClass();
    ...
};

// allocation (simplified)
template<class T> 
T* allocate()
{
    size_t objectSize = sizeof(T);
    T* obj = (T*)malloc(objectSize);
    new(obj) T();
    obj->m_ObjectSize = objectSize;
}

// deallocation (also simplified)
void deallocate(MemoryPoolObject* obj)
{
    // Does this call ~BaseClass() and ~ChildClass()?
    obj->~MemoryPoolObject();
}

Answer 1

所以...如果我进行显式调用~MemoryPoolObject(),那会做正确的事情(包括调用任何多重继承的基类的析构函数)吗？

是的,它会的.

但是,我认为您可以稍微改变策略以使您的代码更直观.

过载operator new和operator delete中MemoryPoolObject,让用户使用operator new,并operator delete以通常的方式.

示例程序:

#include <iostream>
using namespace std;

void* allocate(size_t s)
{
   // This is a simple implementation.
   // To use a memory pool for allocating objects, this function
   // and deallocate() need to be changed accordingly.

   std::cout << "Allocating memory of size " << s << std::endl;
   return new char[s];
}

void deallocate(void* ptr, size_t s)
{
   std::cout << "Dellocating memory of size " << s << std::endl;
   delete [] static_cast<char*>(ptr);
}

class MemoryPoolObject
{
   public:

      virtual ~MemoryPoolObject() {}

      void* operator new (size_t s)
      {
         return allocate(s);
      }

      void operator delete (void* ptr, size_t s)
      {
         return deallocate(ptr, s);
      }
};

class BaseClass
{
   public:
      virtual ~BaseClass() {}
};

class ChildClass : public BaseClass, public MemoryPoolObject
{
   virtual ~ChildClass() {}
};

int main()
{
   MemoryPoolObject* ptr = new ChildClass;
   delete ptr;
}

产量

Allocating memory of size 16
Dellocating memory of size 16