CODEWITHSUNDEEP
c++linked-list
Medvednic
Medvednic

Reputation: 692

Linked lists using nested classes?

I have the class Agency which has a private nested class Node that should be used to build a linked list of Client objects.

In order to add a node I need to use an overloaded += operator that receives a Client object. When I want to add the first object: the function calls the setHead member of the Node class.

But once I try to modify the data members of head: data to point to the received Client object and next to NULL a run-time error occurs.

I can't figure out whats wrong, the Client object is passed as it should be (I checked it) - I think that I'm missing something in the declaration of setHead's arguments.

would be thankful for any advice. btw, I have to use the existing private members as they are and setHead method must receive a pointer to Client.

Agency.h

class Agency
{
    public:
        Agency(); //ctor
        Agency& operator+=(const Client&); //overloaded += operator
        ~Agency(); //dtor
    private:
        class Node //node as nested class
        {
            public:
            Node(); //ctor
            void setHead(Client*&); //set head node
            private:
            Client* data; //points to Client
            Node* next; //points to next node on the list
        };

        Node *head; //points to head node of database
};

Agency.cpp relevant methods

void Agency::Node::setHead(Client*& temp)
{
    data = temp;
    next = NULL;
}
Agency& Agency::operator+=(const Client& client_add)
{   
    Client* temp = new Client (client_add); //new client object is created using clients copy ctor
    if (!head) //if the head node is NULL
    {
        head->setHead(temp); //assign head node to point to the new client object 
    }
        return *this;
}

EDIT: Thanks for the reply, I have yet another question:

I want to have a method of Node that will return a pointer to Node, here is the declaration:

    `Node* nextNode(Node*);`

Function:

    `Node* MatchmakingAgency::Node::nextNode(Node* start)`

Causes compilation error: 'Node' does not name a type

How can I properly declare such a method?

Upvotes: 0

Views: 2595

Answers (1)

eerorika
eerorika

Reputation: 238421

In this code:

if (!head) //in the head node is empty
    {
        head->setHead(temp);

head is not "empty". It's a null pointer. And then you dereference the null pointer which results in undefined behaviour.

Perhaps you meant to have this:

head = new Node();

before setHead.

Upvotes: 3

Related Questions