QListIterator memory corruption

Simon Parzer — Invalid Date

Hello! I have a little trouble understanding how QListIterator/QMutableListIterator work.
The following example is based on a real world application, I just isolated the problematic code so it's easier to understand.
If you want to try it, just create a new console application in Qt Creator and replace main.cpp with this code. I used the precompiled Qt 5.4.2 SDK with the MinGW compiler.

#include 
#include 

struct A {
    A(): a(1), b(1), c(3) {}
    int a, b, c;
};

struct B {
    QList list;
    void inner() {
        QMutableListIterator it(list);
        while (it.hasNext()) {
            it.next().b++;
        }
    }
};

static B b;

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);


    for (int i = 0; i < 10; i++) {
        A a;
        b.list.append(a);
    }

    A* first = &b.list[0];

    {
        QListIterator it(b.list);
        while (it.hasNext()) {
            const A& elem = it.next();
            qDebug() << elem.a << elem.b << elem.c;
        }
        b.inner();
        qDebug() << first->a << first->b << first->c;
    }

    qDebug() << first->a << first->b << first->c;

    return a.exec();
}

Here is the output:

1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
1 1 3
-17891602 -17891602 -17891602

The last two lines puzzle me. I was expecting them both to say "1 2 3", but instead ~QListIterator destructed the list, and I'm reading deallocated memory.
Is this how it is supposed to work, and if yes, why?

Topics tagged with listiterator

QListIterator memory corruption