How to Safely Remove Elements from a C std::list While Iterating?

Iterative Element Removal in C std::List

In C , std::list is a container that provides a doubly linked list data structure. While iterating through a list, it can be necessary to remove elements based on specific conditions. This issue arises when removing items directly within the iteration loop results in an "List iterator not incrementable" error.

To resolve this issue, it is essential to increment the iterator (i ) first before removing the previous element. This can be achieved by utilizing a while loop as follows:

std::list<item*>::iterator i = items.begin();
while (i != items.end())
{
    bool isActive = (*i)->update();
    if (!isActive)
    {
        items.erase(i++); // alternatively, i = items.erase(i);
    }
    else
    {
        other_code_involving(*i);
        ++i;
    }
}

In this revised code, the iterator i is incremented inside the loop, allowing the items.erase(i ) operation to successfully remove the previous element. Alternatively, i can be replaced with i = items.erase(i) for the same effect.

By implementing this approach, items can be removed efficiently and immediately upon satisfying the desired condition, eliminating the need for additional passes through the list.

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