Memory leak in this case?

Hello everyone,


Suppose I have a component (class) CX implements IUnknown interface, and I have retrieved a pointer of CX by IUnknown pointer (IUnknown*), that is.

Code:

---

IUnknown* pCX;
QueryInterface (IID_IUnknown, &pCX);

//...

delete pCX; // memory and resource leak here?

---

Even if I declare the component CX's destructor as virtual, if I delete through IUnknown pointer to "release" the object, there is still potential memory and resource leak, because in IUnknown interface, destructor is the compiler provided default one, which is non-virtual and public, right?


thanks in advance,
George

Quote:

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Originally Posted by George2

Hello everyone,


Suppose I have a component (class) CX implements IUnknown interface, and I have retrieved a pointer of CX by IUnknown pointer (IUnknown*), that is.

Code:

---

IUnknown* pCX;
QueryInterface (IID_IUnknown, &pCX);

//...

delete pCX; // memory and resource leak here?

---

Even if I declare the component CX's destructor as virtual, if I delete through IUnknown pointer to "release" the object, there is still potential memory and resource leak, because in IUnknown interface, destructor is the compiler provided default one, which is non-virtual and public, right?


thanks in advance,
George

---

An interface obtained through QueryInterface always has its refcount increased. The correct way to counter this is to cause the refcount to be decreased again when the interface pointer is no longer needed.
Don't ever explicitly delete COM objects! You should always allow the last Release call to free them.

In this case you should do this:

Code:

---

CComPtr<IUnknown> spCX;
QueryInterface(IID_IUnknown, &spCX);

---

That's it. Now when the CComPtr is destroyed, Release gets called automatically.
Note that this is using ATL, which I use all the time at work. You may have to include some header file(s) that you aren't currently using.

CComPtr is hidden deep within atlbase.h :)
Very nice class, CComPtr.

Thanks iMalc,


Question answered. Cool!!

Quote:

---

Originally Posted by iMalc

An interface obtained through QueryInterface always has its refcount increased. The correct way to counter this is to cause the refcount to be decreased again when the interface pointer is no longer needed.
Don't ever explicitly delete COM objects! You should always allow the last Release call to free them.

In this case you should do this:

Code:

---

CComPtr<IUnknown> spCX;
QueryInterface(IID_IUnknown, &spCX);

---

That's it. Now when the CComPtr is destroyed, Release gets called automatically.
Note that this is using ATL, which I use all the time at work. You may have to include some header file(s) that you aren't currently using.

---

regards,
George