CODEWITHSUNDEEP
c++liststliterator
Gandalf458
Gandalf458

Reputation: 2269

Can a C++ std::list iterator move past the end?

for(std::list<MyClass *>::iterator it = m_currentJobs.begin(); it != m_currentJobs.end(); ++it)
{
    request = *it;
    if(request != NULL)
    {
        printf(request->status());
    }

    delete request;
    m_currentJobs.erase(it);
}

Is it possible for the iterator to point to some garbage data beyond the end of the list?

Upvotes: 1

Views: 682

Answers (2)

user2249683
user2249683

Reputation:

You make your iterator invalid by erasing it.

You may change your loop to:

std::list<MyClass *>::iterator it = m_currentJobs.begin();
while(it != m_currentJobs.end())
{
    // ...
    it = m_currentJobs.erase(it);
}

And to answer your question: Yes it is possible to have an invalid iterator (not limited to iterators past the end). Using these involves undefined behavior.

Upvotes: 6

Stack Overflow is garbage
Stack Overflow is garbage

Reputation: 247909

At the end of each iteration, you do this:

m_currentJobs.erase(it);

which invalidates it.

Immediately afterwards, you do this:

++it

which is undefined behavior if it is not a valid iterator.

Most likely, that is your problem.

std::list::erase actually returns an iterator, pointing to the element after the deleted one. Reset it to point to that, and your code should work a lot better. (Note that when this happens, you've already jumped to the next element, so you shouldn't also run ++it in that iteration.)

Upvotes: 3

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