List iterator not incrementable error message in C++

Question

As a newbie I'm trying to implement a sorting function in C++, using the list-class. However, running the code I get the error that the list iterator is not incrementable... However it seems very unlikely as it should be incrementable!

code:

void shuffle (list<int> &list1)
{
    list<int> smaller;
    list<int> larger;

    if (list1.size() > 1)
    {
        list<int>::iterator it;
        //int it;

        int x = list1.front();


        for (it = list1.begin(); it != list1.end(); it++)
        {                                       
            if(*it <= x)
            {
                smaller.push_front(*it);
                list1.pop_front();

            }
            else
            {
                larger.push_back(*it);
                list1.pop_front();
            }
            shuffle (smaller);
            shuffle (larger);
        }
    }
    else
    {
        print(smaller);
        print(larger);

        //cout << "No sorting needed! The list still looks like: ";
        //print(list1);
    }
    print(smaller);     
    print(larger);
}

I implemented this function just in de CPP file, under the main.

Does anyone has any suggestions?

Solution

Your call to list1.pop_front() removes the element which the iterator is pointing to initially, invalidating it. And an invalid iterator can not be incremented. :)

It took a few minutes to find with the debugger. Just keep an eye on the value of 'it' as you step through the program. I don't know if you know how to use the debugger yet, but if not, do yourself a favor and learn it. It's an invaluable tool.

(By the way, in the future, please be explicit about whether the error occurs at compile-time or while running the program. Your question stated the error occurred when "compiling the program". I just edited the question for you, hope you don't mind. But it's an important distinction, and makes it harder to answer your question accurately)