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Can an object delete itself?

DanG · 2002-08-31T04:28:32

I''m working &#111n a class that is referance counted. Whenever something wants to referance the object they call object->AddRef(); and when done with it they call object->ReleaseRef(); The thing is that the way it is setup now, I have to make the last person holding a referance to delete it. The code becomes like this: if (object->ReleaseRef()) // returns true if this is the last ref { delete object; } A little intricate and convoluted. I want ReleaseRef to delete itself if there are no more referances, but I don''t know how to do this. Anyone have ideas?

General and Gameplay Programming Programming

Started by DanG August 29, 2002 10:23 PM

13 comments, last by DanG 21 years, 7 months ago

TangentZ

450

August 30, 2002 03:54 PM

This hasn''t come up yet.

If you want to be sure you don''t get it wrong, and also want
to be exception-safe, it''s good to have a "smart pointer"
that takes care of adding and subtracting reference counts.

  template <typename T>class RefPtr    {    private:    T *m_pObject;    public:    RefPtr(T *pObject) : m_pObject(pObject)        { pObject->AddRef(); }    RefPtr(const RefPtr &Other) : m_pObject(Other.m_pObject)        { m_pObject->AddRef(); }    ~RefPtr(void)        // Release() returns true if ref count drops to 0        { if (m_pObject->Release()) delete m_pObject; }    const RefPtr &operator=(const RefPtr &Other)        {        if (m_pObject->Release()) delete m_pObject;        m_pObject = Other.m_pObject;        m_pObject->AddRef();        return *this;        }    // end if    T *operator->(void) const        { return m_pObject; }    T &operator*(void) const        { return *m_pObject; }    };// end

This class is by no means complete. I leave that as an
exercise to the reader (i.e. you) to fix the holes.

(Hint: null-pointer (I mean 0) and self-assignment...etc)

Kami no Itte ga ore ni zettai naru!

神はサイコロを振らない！

SabreMan

504

August 30, 2002 04:28 PM

quote:Original post by daerid
Yes, I know. I cheated.

Not only did you cheat, you didn''t allocate a foo object. An object lifetime does not begin until the ctor has completed, and in your code no ctor for foo has been called. Basically, all you''ve achieved is to lie to the compiler, by invoking reinterpret_cast and saying "here''s some storage which is layout compatible with and contains a valid foo instance" (which, of course, it doesn''t). Any calls to foo member functions via f will invoke undefined behaviour. Quite frankly, I wouldn''t be surprised if you''ve had a few demons fly out of your nostrils whilst running that code.

CGameProgrammer

640

August 30, 2002 08:47 PM

Well that''s true, free() fails if the object wasn''t created dynamically. But my point was that Beer_Hunter''s example also does not work because you can use malloc() to create the object.

But I see what you''re saying -- you meant using create() basically guarantees the object is created dynamically instead of just having a static instance of it.

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Beer Hunter

712

August 30, 2002 09:08 PM

quote:Original post by CGameProgrammer
Well that''s true, free() fails if the object wasn''t created dynamically. But my point was that Beer_Hunter''s example also does not work because you can use malloc() to create the object.

I was trying to prevent mistakes - not deliberate stupidity

SabreMan

504

August 31, 2002 04:16 AM

quote:Original post by CGameProgrammer
But my point was that Beer_Hunter's example also does not work because you can use malloc() to create the object.

No you cannot. I've just told you that you haven't created the object with malloc(). Object creation is a 2-step process. First, the storage is allocated. Second the ctor is executed. You've only achieved the first, so the object has *not* been created. If you cannot gain access to the ctor of the object, then you cannot create an instance of that object. Period.

You could create another object that is layout compatible and contains the correct representation, but the effort it requires to do that should tell you that you're doing something wrong. Besides, the point of such techniques is to make it easy for the developer to get things right. It's not possible to prevent people from writing code with malicious intent, other than to fire them.

[edited by - SabreMan on August 31, 2002 5:28:32 AM]

Can an object delete itself?

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