C++ Delete Operator

Question

I'm relatively new to C++ and I have an issue which I really do not understand. My code creates a linked list. It is actually longer than this, but I chopped it down for the purpose of this question.

When I run the code, it adds three nodes and then when it goes to delete the node with the URI b , it calls the delete operator and ends up deleting the node, but then it seems to go back to delete operator (when I step through it) and it kills my whole list.

#include <iostream>
#include <string>
#include <cstdlib>
#include <cstdio>

using namespace std;


class CLinkedList
{
protected:
    class ip_uri_store
    {
    public:
        string uri, ip;
        ip_uri_store* next;

        ip_uri_store(const string& URI, const string& IP) {uri = URI, ip = IP, next = NULL;}
    };
    typedef ip_uri_store* nodeAddress;

    nodeAddress head;

    void AddNode(const string&, const string&, nodeAddress);
    void DeleteNode(const string&, nodeAddress, nodeAddress);

public:
    CLinkedList() {head = NULL;}
    void AddNode(const string& URI, const string& IP) {AddNode(URI, IP, head);}
    void DeleteNode(const string& URI) {DeleteNode(URI, head, head);}

};

void CLinkedList::AddNode(const string& URI, const string& IP, nodeAddress node)
{
    nodeAddress temp = new ip_uri_store(URI, IP);
    temp->uri = URI;
    temp->ip = IP;
    temp->next = head;
    head = temp;
}

void CLinkedList::DeleteNode(const string& URI, nodeAddress node, nodeAddress behindNode)
{
    if(node)
    {
        if(!node->uri.compare(URI))
            node == head ? head = head->next : behindNode->next = node->next;
        else
            DeleteNode(URI, node->next, node);

        delete node;
    }
}



int main(int argc, char* argv[])
{
    CLinkedList lList;
    lList.AddNode("a", "1");
    lList.AddNode("b", "2");
    lList.AddNode("c", "3");
    lList.DeleteNode("b");

    return 0;
}

Answer 1

You are calling delete node; even if the comparison fails (ie node->uri != URI ).

if(!node->uri.compare(URI))
{
    node == head ? head = head->next : behindNode->next = node->next;
    delete node;
}
else
    DeleteNode(URI, node->next, node);

Also, the condition seems to be inverted.

Answer 2

First, you should use std::list and avoid reinventing the world. Anyway, if you are stuck to this implementation for some reason :

• temp->uri = URI; and temp->ip = IP; in the AddNode method are useless because the members are already initialized in the constructor of ip_uri_store class.
• the deletion of the head of the list occurs because the 'delete node' should only be done in the case node->uri.compare(URI) in the DeleteNode method.

Again, you should seriously consider using standard classes...

Answer 3

You are calling delete on all the nodes. It needs to be moved inside the conditional so you only delete the nodes that match the URI

if(!node->uri.compare(URI)) {
    node == head ? head = head->next : behindNode->next = node->next;
    delete node;
} else {
    DeleteNode(URI, node->next, node);
}