C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Deleting Pointers from STL Vector Goto page 1, 2  Next          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Hanzo Guest Posted: Thu Oct 02, 2003 10:18 am    Post subject: Deleting Pointers from STL Vector I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: 1. Before the delete, toDie and m_cdPlayer1 have a value of 0x00a72498. 2. After the delete, both toDie and m_cdPlayer1 have their __vfptr point to memory 0xFEEEFEEE (signifying a delete) 3. After the set-to-null, the value of toDie becomes 0x00000000, while m_cdPlayer1 remains at a value of 0x00a72498 (while still pointing to 0xFEEEFEEE). Not the behavior I want. At this point, m_cdPlayer1 is officially deleted, yet the test "if (m_cdPlayer)" fails, since it is technically not NULL. Any suggestions or recommendations on how to get the intended behavior out of this snippet? - Hanzo [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Peter van Merkerk Guest Posted: Thu Oct 02, 2003 8:04 pm    Post subject: Re: Deleting Pointers from STL Vector Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; After those lines toDie runs out of scope; why bother setting it to NULL? Quote: I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. 'toDie = NULL;' only sets the toDie pointer to NULL it does not affect the object it was pointing to. Note that that object no longer exists at the point toDie is being set to NULL because it was deleted just before that line. -- Peter van Merkerk peter.van.merkerk(at)dse.nl [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Randy Maddox Guest Posted: Thu Oct 02, 2003 11:44 pm    Post subject: Re: Deleting Pointers from STL Vector Hanzo <hanzo (AT) milclan (DOT) com> wrote Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; Here toDie is a COPY of the pointer referenced by the iterator i. When you later set toDie to NULL (and why not just 0?) you are only setting that copy, and of course not the original pointer it was copied from. All you need to do is to make toDie be a reference to the pointer of interest, rather than a copy of it. Simply change the above declaration to: CDrawableObject* &toDie = *i; and all will work as you expect. Randy. Quote: // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } { Snip of unreferenced quoting. -mod/jep } [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Bob Bell Guest Posted: Thu Oct 02, 2003 11:49 pm    Post subject: Re: Deleting Pointers from STL Vector Hanzo <hanzo (AT) milclan (DOT) com> wrote Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: 1. Before the delete, toDie and m_cdPlayer1 have a value of 0x00a72498. 2. After the delete, both toDie and m_cdPlayer1 have their __vfptr point to memory 0xFEEEFEEE (signifying a delete) 3. After the set-to-null, the value of toDie becomes 0x00000000, while m_cdPlayer1 remains at a value of 0x00a72498 (while still pointing to 0xFEEEFEEE). Not the behavior I want. At this point, m_cdPlayer1 is officially deleted, yet the test "if (m_cdPlayer)" fails, since it is technically not NULL. Any suggestions or recommendations on how to get the intended behavior out of this snippet? Put boost::shared_ptrs in your vector (no delete needed, just erase from the vector), and use boost::weak_ptr as m_cdPlayer1. That should do what you want. http://www.boost.org. Bob [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Philipp Bachmann Guest Posted: Fri Oct 03, 2003 9:33 am    Post subject: Re: Deleting Pointers from STL Vector Quote: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. Yes, because you "delete" the object both "toDie" and your vector element points to, but modify only the (automatic) poiter "toDie". As usual with pointers, there's a difference between the pointer and the value / instance it points to. So it has not much to do with "std::vector<>" nor with C++. Quote: In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: Do you mean, that "m_cdPlayer1" is an instance, not a pointer? If so, you cannot achieve your goal. So "m_cdPlayer1" _must_ be a pointer. Quote: Any suggestions or recommendations on how to get the intended behavior out of this snippet? The misconception is, that "vector<CDrawableObject*>" is the wrong type for your usage. You should store pointers to (member) pointers instead like this: "vector< CDrawableObjects *CGame::* > v;" Now "delete myGame.*v[42]; myGame.*v[42]=0;" will do the trick. In other words, you need one further indirection in addressing. Cheers, Philipp. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Antoun Kanawati Guest Posted: Fri Oct 03, 2003 9:37 am    Post subject: Re: Deleting Pointers from STL Vector Hanzo wrote: Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: 1. Before the delete, toDie and m_cdPlayer1 have a value of 0x00a72498. 2. After the delete, both toDie and m_cdPlayer1 have their __vfptr point to memory 0xFEEEFEEE (signifying a delete) 3. After the set-to-null, the value of toDie becomes 0x00000000, while m_cdPlayer1 remains at a value of 0x00a72498 (while still pointing to 0xFEEEFEEE). Not the behavior I want. At this point, m_cdPlayer1 is officially deleted, yet the test "if (m_cdPlayer)" fails, since it is technically not NULL. Any suggestions or recommendations on how to get the intended behavior out of this snippet? Try working with vector<CDrawableObject **>. This has enough indirection to give you the "desired" effect. You'll need to write: delete *toDie; *toDie = NULL; Having said that, the real problem appears to be a misunderstanding of pointers and indirection. The variable toDie is a local variable, the assignment 'toDie = NULL' merely sets that variable to NULL. A different variable, of the same type and value (m_cdPlayer) is not affected at all. However, due to the interpretation of the type (pointer to CDrawableObject), and the statement 'delete toDie;' the variable m_cdPlayer holds a value that is no longer valid. The expectation that 'toDie = NULL' will affect any other variable, under the conditions stated above, indicates a misunderstanding of pointer indirection and iterators. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Marc Schellens Guest Posted: Fri Oct 03, 2003 11:18 am    Post subject: Re: Deleting Pointers from STL Vector Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. {over quote snipped -mod} Any suggestions or recommendations on how to get the intended behavior out of this snippet? setting toDie = NULL is useless as it get overwritten in the next iteration and it is unkown outside the block is is declared in anyway. setting (*i) to NULL marks at least in your vector that the element is deleted. If the only pointer is in your vector, you are there. But as you describe it, that is not the case. Realize that you deleting an object does not change any pointer to that object. Probably you need to rewrite some of your program. One possible solution would be to keep all pointers to your objects in only one vector and using iterators to this vector to access them. hdh, marc [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Hanzo Guest Posted: Fri Oct 03, 2003 11:25 am    Post subject: Re: Deleting Pointers from STL Vector On 2 Oct 2003 16:04:00 -0400, "Peter van Merkerk" <merkerk (AT) deadspam (DOT) com> wrote: Quote: 'toDie = NULL;' only sets the toDie pointer to NULL it does not affect the object it was pointing to. Note that that object no longer exists at the point toDie is being set to NULL because it was deleted just before that line. ok, well, the goal of deleting toDie and then setting it to NULL were the hopes of deleting the *original* variable, and setting *it* to NULL (in this case, m_cdPlayer1). So, in order to accomplish that, do I need to skip the entire toDie assignment step and just: delete *i; *i = NULL; ? - Hanzo [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top John Potter Guest Posted: Fri Oct 03, 2003 11:28 am    Post subject: Re: Deleting Pointers from STL Vector On 2 Oct 2003 06:18:39 -0400, Hanzo <hanzo (AT) milclan (DOT) com> wrote: Quote: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); This removes the pointer from the vector. Since we are about to delete the pointee, ownership by the vector is assumed. The whole point of this exercise is that delete **i; i = g_vecGameObjects.erase(i); may have undefined behavior because we do not know what might be done with the invalid pointer by erase. Paranoid code. Quote: // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. The original variable of type pointer which had the same value as toDie has been erased from the vector and does not exist. Quote: In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: If that is true, there is an ownership problem and the whole program is a total mess. The CDrawableObjects* is a pointer to an object allowcated on the heap and owned by that pointer. If there are any other pointers to that heap object, it is a bug in the program. John [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Manuel Guest Posted: Fri Oct 03, 2003 11:30 am    Post subject: Re: Deleting Pointers from STL Vector "Hanzo" <hanzo (AT) milclan (DOT) com> a écrit: Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; possible fix... CDrawableObject*& toDie = *i; Quote: // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } [snip] cheers, - Manuel to reply, swap the name with the domain. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jorge Schramm Guest Posted: Fri Oct 03, 2003 11:32 am    Post subject: Re: Deleting Pointers from STL Vector Hi Hanzo, if you want to manipulate the _original_ pointer m_cdPlayer, you must use a vector of pointers to pointers: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject**>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((**i) && (**i)->CanRemove()) { delete **i; **i = NULL; i = g_vecGameObjects.erase(i); } else ++i; } } Hope this helps Jorge [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Aaron Bentley Guest Posted: Fri Oct 03, 2003 11:42 am    Post subject: Re: Deleting Pointers from STL Vector Hanzo wrote: Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. Right. ToDie is just a plain pointer. You initialized it with the value of (*i), then changed its value. Personally, I'd rewrite it so you don't reset i immediately: Quote: if ((*i) && (*i)->CanRemove()) { // erase... Vector<CDrawableObject*>::iterator i2 = g_vecGameObjects.erase(i); // ...and kill delete *i; *i = NULL; i=i2; } But the way to do what you want is a reference-to-pointer: if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject*& toDie = *i; //note ampersand // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } -- Aaron Bentley www.aaronbentley.com [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top John Potter Guest Posted: Fri Oct 03, 2003 11:45 am    Post subject: Re: Deleting Pointers from STL Vector On 2 Oct 2003 19:44:52 -0400, [email]rmaddox (AT) isicns (DOT) com[/email] (Randy Maddox) wrote: Quote: Hanzo <hanzo (AT) milclan (DOT) com> wrote Quote: if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; Here toDie is a COPY of the pointer referenced by the iterator i. When you later set toDie to NULL (and why not just 0?) you are only setting that copy, and of course not the original pointer it was copied from. All you need to do is to make toDie be a reference to the pointer of interest, rather than a copy of it. Simply change the above declaration to: CDrawableObject* &toDie = *i; and all will work as you expect. I doubt it. Quote: // erase... i = g_vecGameObjects.erase(i); Make dangling reference. Quote: // ...and kill delete toDie; Kaboom! John [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Sat Oct 04, 2003 1:51 am    Post subject: Re: Deleting Pointers from STL Vector Hanzo <hanzo (AT) milclan (DOT) com> wrote Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: void CGame::RemoveDeadObjects() { // cleanup crew!! vector<CDrawableObject*>::iterator i; for (i = g_vecGameObjects.begin(); i != g_vecGameObjects.end() { // if object is not null and can be removed... if ((*i) && (*i)->CanRemove()) { // grab hold before erasure CDrawableObject* toDie = *i; // erase... i = g_vecGameObjects.erase(i); // ...and kill delete toDie; toDie = NULL; } else ++i; } } Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. Normal, no. You told the compiler to set toDie to NULL. You didn't tell it to do anything else. In this case, setting toDie to NULL is for all intents and purposes a no-op, and a any halfway good optimizing compiler will eliminate the line completely. I'm not sure what you mean by "the original variable". The variable toDie contains a copy of the element which was in the vector. This element has been erased. It doesn't exist any more, so it can't be set to NULL. There may, of course, be other variables designating the element. The compiler has no way of knowing this, and it is your responsibility to manage them. There are several alternatives, according to your needs: - If just setting them to null is sufficient, there are different types of smart pointers. If you use boost::shared_ptr in the array, any boost::weak_ptr pointing to the object will appear to be NULL; in many cases, this is a sufficient solution. If for some reason, using boost::shared_ptr is not an alternative (although frankly, I cannot think of one), I have a ManagedPtr at my site which will automatically become null when the pointed to object is destructed; it is considerably less flexible than the Boost solution, however, since it places significant constraints on the pointed to object. - If you are storing the pointers in other collections, say because another object might want to refer to several GameObjects, then you also need some way of removing the pointers from the collection entirely, to avoid memory leaks. The simplest way to do this is just to use weak_ptr, as above, and scan the collection periodically (say each time you modify it) to suppress any weak_ptr whose objects no longer exist. If the collections are really large, however, this may have unacceptable runtime overhead. In such cases, you need some means of informing the collection; this implies some sort of notification mechanism, in which the collection is a listener. My ManagedPtr uses a notification to inform the pointers to be set to null, and could easily be adopted to handle additional notifications. While this is definitely overkill when the first solution works, if you do need notification, the added complexity that ManagedPtr introduces will be necessary anyway. - More generally, it may be that the object holding a pointer to the deleted object needs to do more than just delete the relationship. In this case, you need to use the Observer pattern. The destructor of the object informs all classes which have expressed an interest in it that it is going to die, and they do whatever they have to do. Quote: In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: 1. Before the delete, toDie and m_cdPlayer1 have a value of 0x00a72498. 2. After the delete, both toDie and m_cdPlayer1 have their __vfptr point to memory 0xFEEEFEEE (signifying a delete) I think you are speaking about something in the pointed to object itself. If both pointers point to the same address, it is normal that reading through either pointer will result in the same thing. Quote: 3. After the set-to-null, the value of toDie becomes 0x00000000, while m_cdPlayer1 remains at a value of 0x00a72498 (while still pointing to 0xFEEEFEEE). What else should (or even could) happen. The compiler has no way of knowing which objects might or might not have pointers to the same place as toDie. Changing toDie changes toDie, and nothing else in the program. Quote: Not the behavior I want. At this point, m_cdPlayer1 is officially deleted, yet the test "if (m_cdPlayer)" fails, since it is technically not NULL. Any suggestions or recommendations on how to get the intended behavior out of this snippet? See above. The easiest solution to begin with is to use boost::shared_ptr in the vector, and boost::weak_ptr every where else. But sooner or later, you'll run into a case where you need full notification; every professional I know of has some sort of change notification mechanism in his toolbox. -- James Kanze GABI Software mailto:kanze (AT) gabi-soft (DOT) fr Conseils en informatique orientée objet/ http://www.gabi-soft.fr Beratung in objektorientierter Datenverarbeitung 11 rue de Rambouillet, 78460 Chevreuse, France, +33 (0)1 30 23 45 16 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top WW Guest Posted: Thu Oct 09, 2003 8:09 pm    Post subject: Re: Deleting Pointers from STL Vector Hanzo wrote: Quote: I'm iterating over a vector of base class pointers and deleting those which meet a certain criteria...i'm using pretty text-book code for the particular delete/erasure (it's straight out of Myers' Effective STL), and reads like this: [SNIP] Here's the problem: on the two lines that say delete toDie; toDie = NULL; I am noticing that the original variable to which toDie is pointing is not being set to NULL, just "toDie" itself. In other words, if one of the CDrawableObjects* was say, a member var of CGame called m_cdPlayer1, when the delete/set-to-NULL happens: 1. Before the delete, toDie and m_cdPlayer1 have a value of 0x00a72498. 2. After the delete, both toDie and m_cdPlayer1 have their __vfptr point to memory 0xFEEEFEEE (signifying a delete) 3. After the set-to-null, the value of toDie becomes 0x00000000, while m_cdPlayer1 remains at a value of 0x00a72498 (while still pointing to 0xFEEEFEEE). Not the behavior I want. At this point, m_cdPlayer1 is officially deleted, yet the test "if (m_cdPlayer)" fails, since it is technically not NULL. Any suggestions or recommendations on how to get the intended behavior out of this snippet? I see no m_Player in your code snippet. So I have no idea. However I have few information for you: 1.) std::vector stores a copy of whatever thing it stores. The pointer inside the vector has absolutely no connection to the m_cdPlayer1 member variable it has been copied from. 2.) toDie is a copy of what was inside the vector. It has no connection to the pointer pointed by the iterator. It makes absolutely no sense to set it to NULL, since in the next line (at the }) it ceases to exist. If you want to be able to change the original pointer, you will need to use a pointer to pointer and store that in the vector. -- WW aka Attila [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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