Language: C
Label: vulnerable
CWE: CWE-416 \u2014 Use After Free
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Code:
is_qf_win(win_T *win, qf_info_T *qi)
{
    // A window displaying the quickfix buffer will have the w_llist_ref field
    // set to NULL.
    // A window displaying a location list buffer will have the w_llist_ref
    // pointing to the location list.
    if (bt_quickfix(win->w_buffer))
	if ((IS_QF_STACK(qi) && win->w_llist_ref == NULL)
		|| (IS_LL_STACK(qi) && win->w_llist_ref == qi))
	    return TRUE;

    return FALSE;
}