Databases
StackOverflow2013
Postsdbo
POC++ linked list help (pointers)?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POC++ linked list help (pointers)?
    primarykey
    data
    text
    <pre><code>template &lt;typename T&gt; class LinkedNode { public: T data; LinkedNode&lt;T&gt; *next; LinkedNode&lt;T&gt; *prev; LinkedNode&lt;T&gt;(); LinkedNode&lt;T&gt;(T); }; // Default constructor template &lt;typename T&gt; LinkedNode&lt;T&gt;::LinkedNode() { next = NULL; prev = NULL; } template &lt;typename T&gt; class LinkedList { private: LinkedNode&lt;T&gt; *head; public: LinkedList&lt;T&gt;(); ~LinkedList&lt;T&gt;(); void addFront(T); void addBack(T); void addAt(T, int); void removeFront(); void removeBack(); void removeAt(int); void printList(); }; // Constructor template &lt;typename T&gt; LinkedList&lt;T&gt;::LinkedList() { head = NULL; } // Add new node to front template &lt;typename T&gt; void LinkedList&lt;T&gt;::addFront(T d) { LinkedNode&lt;T&gt; temp; temp.data = d; if (head == NULL) { head = &amp;temp; } else { temp.next = head; head-&gt;prev = &amp;temp; head = &amp;temp; } } // Add new node to back template &lt;typename T&gt; void LinkedList&lt;T&gt;::addBack(T d) { // Find the back of this list LinkedNode&lt;T&gt; *ptr; ptr = head; while (ptr-&gt;next != NULL) // &lt;------- DIES HERE, MEMORY ACCESS VIOLATION { ptr = ptr-&gt;next; } // Make a new node and join it to the back LinkedNode&lt;T&gt; temp; temp.data = d; temp.prev = ptr; ptr-&gt;next = &amp;temp; } </code></pre> <p>Here is a snippet from my linked list system. The issue is that it throws an error on the indicated line. The debugger says that the "head" pointer is pointing to a legitimate memory address of a LinkedNode with no "next" or "prev", but the "ptr" pointer points to address 0xcccccc, not the address of head? I'm really confused, I thought I understood pointers!</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USuser745668
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COIn general, 0xcccccc is the debugger telling you the memory being pointed to is uninitialized garbage. If the debugger is right, since ptr=head is correct, the error is in the loop. ptr became junk after ptr = ptr->next. So somehow there is a mistake in the chain.
      singulars
      1. POC++ linked list help (pointers)?
      1. USVoidStar
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload