Question

I’m trying to learn C++ and there is a small confusion I have.

The text which I am learning from tells me that if I want to delete a node of type const T& I should first create a new pointer of that node type, then delete it using the inbuilt C++ delete[]. However, what happens if I just set the link from the to-be-deleted node’s previous element to the to-be-deleted node’s next element? Something like:

*p = node.previous;
p-> next = node.next;

Or will this cause a memory leak?

I’m confused because I read somewhere else to never, ever delete pointers willy-nilly, but the example code I am working with has something along the lines of:

Node<T> *p = node-to-be-deleted;
delete p;

What is the best way to delete the node?

Answer 1

Assuming your node looks like this:

struct Node
{
    Node*  previous;
    Node*  next;

    SomeType data;
};

Then:

*p = node.previous;
p-> next = node.next;

Then YES. This will cause a memory leak.
It also leaves p->next->prev pointing at the wrong node.

I’m confused because I read somewhere else to never, ever delete pointers willy-nilly, but the example code I am working with has something along the lines of:

Yes the best way is to “never delete pointers”. But this has to go along with some context. You should not be deleting pointers manually because pointers should be managed by an objects that control their lifespan. The simplest of these objects are smart pointers or containers. But for this situation that would be overkill (as you are creating the container).

As you are creating the container (a list) you will need to do the management yourself (Note C++ already has a couple of lost types std::list for a list of values of type t or boost::ptr_list for a list of pointers to T). But it is a good exercise to try and do it yourself.

Here is an example on code review of a beginner making a list and the comments it generated:

http://codereview.stackexchange.com: Linked list in C++

I hope this helps in explains on how to create and delete objects.