I've got code which loops through a list using an iterator. It performs a check on that object and if the condition fails, the item is deleted using the list::erase() method.


std::list<cHBGameObject*>::iterator i;

//remove any object that has passed the cutoff
if(!lObjects.empty())
{
i = lObjects.begin();

while (i != lObjects.end())
{
if((*i)->checkIfOverDeletionThreshold(xDeletionPoint))
lObjects.erase(i);
else
++i;
}

}


In this case, the crash occurs if there is only 1 remaining object and the object is deleted, then when it returns to the "while" statement, the error is thrown.

I can sort of see where I'm going wrong, I think when it hits "while", because the list is empty, it may be that the iterator no longer points to anything valid. I have looked up examples to make sure I'm not doing it wrong but every analogous example I have seen have suggested this approach to looping through a list where you may delete objects. Besides, being able to delete objects in this manner is one of lists' advantages over vectors, no?

Could someone kindly point out where I am going wrong?

The erase method returns a new iterator pointing to the next element. Try something like this:


while(i != objects.end()) {
if(i->delete())
i = objects.erase(i);
else
++i;
}

Apologies, I fixed it, here was the problem:

std::list<cHBGameObject*>::iterator i;

//remove any object that has passed the cutoff
if(!lObjects.empty())
{
i = lObjects.begin();

while (i != lObjects.end())
{
if((*i)->checkIfOverDeletionThreshold(xDeletionPoint))
lObjects.erase(i);
else
++i;
}

}

the bolded bit needed to be changed to:


i = lObjects.erase(i);

So that i recieved a valid pointer after the erasure.

Sorry for the wast of time, though if someone else stumbles on this problem, I hope this helps

Edit: Thanks Erik, I just spotted that myself

When you erase something you invalidate the iterator. Try this instead:



//...
if((*i)->checkIfOverDeletionThreshold(xDeletionPoint))
i = lObjects.erase(i);
else
++i;
// ...


EDIT: was waaaay too slow