CODEWITHSUNDEEP
clinked-list
namarino41
namarino41

Reputation: 123

Printing linked List infinite loop C

I'm trying to print a linked list after having added a node. I have a dummy node to start the list

   Node **nodeArray;
    nodeArray = malloc(10 * sizeof(Node *));

    int i;
    for (i = 0; i < 10; i++) {
        nodeArray[i] = malloc(sizeof(Node));    
    }

    if (userChoice == 'a') 
        add(&nodeArray, setNumber);

void add(Node ***nodeArray, int setNumber) {
        char userString[5];
        printf("Please enter some data: ");
        scanf("%s", userString);

        Node *head = *nodeArray[setNumber];     /* head pointer to first element of array (dummy) */
        Node *newNode = malloc(sizeof(Node));   /* new node to be added to array */

        strncpy(newNode->data, userString, sizeof(newNode->data));  /* copies string entered by the user to data field of new node */
        newNode->next = NULL;   /* initializes next field of new node to NULL */

        Node *tmp = head;   /* pointer to head of list */

        while (!tmp->next) {
            tmp->next = newNode;    /* inserts new node into array */
            tmp = newNode;      /* points head to newly added node */
        }

        tmp = head;     /* points tmp back to head of list */

        printf("List is: ");
        while (tmp->next) {
            printf("%s", (tmp->data));
            tmp = tmp->next;
        }
}

But when I print, I get an infinite loop printing out the data field of the newly added node. Terrible with linked lists....what am I doing wrong?

Upvotes: 0

Views: 1400

Answers (4)

Sanich
Sanich

Reputation: 1845

You made a closed circle link list by this lines:

while (!tmp->next) {
    tmp->next = newNode;    /* inserts new node into array */
    tmp = newNode;          /* points head to newly added node */
}

so after this actually you get newNode->next = newNode which is `tmp->next = tmp.

So instead of this you should do this: 

while (tmp->next) {
    tmp = tmp->next;    //Find the last node
}
tmp->next = newNode;    //Inserts new node into the end of the array

Upvotes: 1

k3oy
k3oy

Reputation: 531

while (tmp->next) {
   tmp->next = newNode;    /* inserts new node into array */
   tmp = newNode;      /* points head to newly added node */
}

In this snippet you're losing the refrence to the next node, and just adding the newNode next to the head. For instance you have the following list:

[1]->[2]->[3]

And you want to push a new element into that list: [4], what happens when you execute your push function (the snippet above) is:

tmp = head; // tmp = [1]
while(tmp->next) {
    tmp->next = newNode; // [1]->next = [4]
    tmp = newNode; // tmp = [4]
}

So the next time '(tmp->next)' is evaluated it will be evaluated as: [4]->next and it will be NULL, breaking the loop. Your list will then be:

[1]->[4]

The other elements are lost because you don't have a reference pointing to them anymore, this is called a memory leak because you won't be able to free them later.

You could write your push function this way:

tmp = head;
while(tmp->next)
    tmp = tmp->next;
tmp->next = newNode // Adds new node to the tail of the linked list

Upvotes: 1

Shai Shprung
Shai Shprung

Reputation: 146

I assume you are trying to add the new Node to the end of your array (aka push). so try this:

Node tmp=head; /* pointer to the head of list */
while (tmp->next) tmp=tmp->next; /* step from Node to Node till the last one */
tmp->next=newNode; /* tell that last one to point to the new Node you created */

Upvotes: 1

rodolk
rodolk

Reputation: 5907

This is because after this:

while (!tmp->next) {
    tmp->next = newNode;    /* inserts new node into array */
    tmp = newNode;      /* points head to newly added node */
}

head points to newNode and newNode->next points to newNode.

That's the problem. Actually the insertion of a newNode is a problem. You will have to change it.

Upvotes: 1

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