Pointer members of a class during assignment operator overloading

Question

I'm trying to write a tree construction program in c++. (it's McCreight's suffix tree) but i have problem with assignment operator overloading for Nodes, specifically of a pointer attribute within my class Node! I have this code in my tree construction method which is not working (explained below):

void ST::insert(int suffix, Node& leaf)
{
    .
    .
    .
    leaf=find_path(u.suffix);
    cout<<leaf.id<<" "<<leaf.parent->id<<'\n';
    .
    .
    .
}

Node ST::find_path(Node* node, int suffix)
{
    .
    .
    .
    cout<<leaf.parent->id<<'\n';
    return leaf;
}

The cout in find_path prints the correct parent id, but when returning the node to insert() it's parent is being lost. cout in insert prints the correct "leaf id" but it doesn't know the "leaf's parent id".

My code for Node class is like this:

class Node
{
public:
    int id;
    Node* parent;
    vector <Node> children;
    vector <int> startPointer;
    Node* SL;
    int strDepth;
    Node()
    {
        parent=NULL;
        SL=NULL;
    }

Node& operator=(const Node node2)
{
    this->id=node2.id;
    if(this != &node2 && node2.parent!=NULL && node2.SL!=NULL)
    {
        *parent = *(node2.parent);
        parent = (node2.parent);
        *SL=*(node2.SL);
    }
    this->children=node2.children;
    this->startPointer=node2.startPointer;
    this->strDepth=node2.strDepth;
}

I have tried many ways to change this overloaded operator but each way giving some other error (usually runtime like NullPointerException), the code I included here is the one which gives the best answer so far, but unless i find a way to know the parent of the returned node i can't finish this! of course i can return the parent and grandparent as separate nodes but that's not interesting. Any help is really appreciated. Thank you!

Your code has many issues: First, the assigment operator (Except you are implementing it doing something like the copy and swap idiom) must get its parameter by const reference, not by value. Second: You have broken The Rule Of Three: You should implement a custom copy ctor, a (correct) assigment operator, and a destructor. — Manu343726
– Manu343726, Commented Apr 5, 2014 at 18:54
thank you! but would you mind saying why is copy ctor required if i'm not going to use that ctor in my code? wouldn't just overloaded = operator do the same thing? (and i have the destructor but i haven't copied all the code here!) i copied this constructor just to show that every node's parent pointer is initialized by NULL, so it can not result in error! thanks. — armen
– armen, Commented Apr 5, 2014 at 21:06

Deduplicator · Accepted Answer · 2014-04-05 19:21:27Z

1

Use std::shared_pointerfor links to nodes, and std::weak_pointer for backlinks.

You might specialise shared_pointer for your class, so that the added bookkeeping data is stored in the node itself. Look at enable_shared_from_this<T>.

edited Apr 5, 2014 at 19:21

answered Apr 5, 2014 at 18:54

Deduplicator

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1 Comment

armen Over a year ago

this is smart and helpful! thank you so much! i've changed my pointers, trying to debug now! i didn't know at all about shared and weak ptrs.

Remy Lebeau · Accepted Answer · 2014-04-05 19:03:38Z

0

Your assignment operator is not implemented correctly. Try this instead:

Node& operator=(const Node &node2)
{
    if(this != &node2)
    {
        this->id=node2.id;
        this->parent = node2.parent;
        SL=node2.SL;
        this->children=node2.children;
        this->startPointer=node2.startPointer;
        this->strDepth=node2.strDepth;
    }
    return *this;
}

In which case, you could just omit the operator altogether and let the compiler auto-generate a default operator for you, as it would generate the same code.

answered Apr 5, 2014 at 19:03

Remy Lebeau

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1 Comment

armen Over a year ago

thanks. i tried this (again), but the cout in find_path() gives 8 as parent id, and the cout in insert() gives 5696520!

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