Question

Possible Duplicate:
When to use virtual destructors?

---

[Second dicuss]
hi,guys! You are all talking about virtual-destructor.
And also i think about the base class`s destructor.
But another test as this:
class A
{
public:
A()
{
}
virtual void fun()
{
}
private:
int mIntA;
};

when class A have a vitual function(not virtual-destrcutor),
it`s ok. Deleting ptrA is OK!

So, i think A just need a vptr to activate the polymorphic. Not class As
destructor must be virtual.
Class As destructor being not virtual just can make resources is not released
correctly.

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class A
{
 public:
  A()
  {
  }
  /*virtual*/ ~A()
  {
  }
 private:
  int mIntA;
};

class B : public A
{
public:
 B()
 {
  mIntB = 1234;
 }

 virtual ~B()
 {
  int i = 0;
 }

private:
 int mIntB;
};

I have a class A. And a class B derived form A;
A doesn`t have any virtual function.
so when i do this:

A* ptrA = new B;
delete ptrA;

it crashes!

but when add a virtual fun to A. it`s ok.
as we know, ptrA is a B object.
but why is it?

Answer 1

The A class isn’t polymorphic, therefore the delete has no possibility to know that ptrA actually points inside an allocated block and therefore the deallocation crashes.