Thread: Pointers to pointers in linked lists

  1. #1
    Registered User
    Join Date
    Mar 2008

    Pointers to pointers in linked lists

    Hi all,

    I'm a beginner in C++ trying to write himself a class for a new datatype that wouldn't be as "inflexible" as the default ones concerning storage capacity. I'm using linked lists to store the value of the number, and I wrote this piece of code to add a node to the end of the list, but I have absolutely no idea if it'll work. In fact, knowing how my experiments usually end, I have a hunch it won't But just to be sure, could anyone go over the code and tell me if it'll work or not?

    void large::createNode(storage_list** param) {
        storage_list *temp; //Create a temporary pointer
        temp = new storage_list; //Allocate memory
        temp->next_node = NULL; //Set pointer to next node
        temp->previous_node = *param; //Set pointer to previous node
        *param->next_node = temp; //Assign "value"
        lastNode = temp; //Set pointer defined in class large

    large is the class, and storage_list is the linked list (actually it's a double-linked list, isn't it...?)

    Thanks in advance ;-)

  2. #2
    Frequently Quite Prolix dwks's Avatar
    Join Date
    Apr 2005
    Just one thing: instead of this
    *param->next_node = temp; //Assign "value"
    I think you want this.
    (*param)->next_node = temp; //Assign "value"
    Operator precedence dictates that without the parentheses, your code is like this:
    *(param->next_node) = temp; //Assign "value"
    And I'm pretty sure that's not what you want, especially since param->next_node should be NULL at this point unless you want a memory leak . . . .

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  3. #3
    Registered User
    Join Date
    Mar 2008
    yes, you're right, I didn't realize that :-) Thx for the help

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