Pointers to pointers in linked lists

G4B3 · 07-22-2008, 03:37 PM

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?

Code:

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 ;-)

dwks · 07-22-2008, 03:47 PM

Just one thing: instead of this

Code:

*param->next_node = temp; //Assign "value"

I think you want this.

Code:

(*param)->next_node = temp; //Assign "value"

Operator precedence dictates that without the parentheses, your code is like this:

Code:

*(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 . . . .

G4B3 · 07-23-2008, 03:54 AM

yes, you're right, I didn't realize that :-) Thx for the help

07-22-2008, 03:37 PM	#1
G4B3 Registered User Join Date: Mar 2008 Posts: 71	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? Code: 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 ;-)
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07-22-2008, 03:47 PM	#2
dwks Frequently Quite Prolix Join Date: Apr 2005 Location: Canada Posts: 7,629	Just one thing: instead of this Code: param->next_node = temp; //Assign "value" I think you want this. Code: (param)->next_node = temp; //Assign "value" Operator precedence dictates that without the parentheses, your code is like this: Code: (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 . . . . __________________ dwk Seek and ye shall find. quaere et invenies.* "Simplicity does not precede complexity, but follows it." -- Alan Perlis "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra "The only real mistake is the one from which we learn nothing." -- John Powell Other boards: DaniWeb, TPS Unofficial Wiki FAQ: cpwiki.sf.net My website: http://dwks.theprogrammingsite.com/ Projects: codeform, xuni, atlantis, etc. New project: nort
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07-23-2008, 03:54 AM	#3
G4B3 Registered User Join Date: Mar 2008 Posts: 71	yes, you're right, I didn't realize that :-) Thx for the help
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