head pointer(linked list)

This is a discussion on head pointer(linked list) within the C Programming forums, part of the General Programming Boards category; Hi, I want to define a pointer, but I am very confused about head pointer, if i define a struct, ...

  1. #1
    Ausandy
    Guest

    Unhappy head pointer(linked list)

    Hi, I want to define a pointer, but I am very confused about head pointer, if i define a struct, like
    typedef struct name{
    int i;
    struct node *next;
    // should I define a head here?
    // like: struct node *head;
    }node;
    // I'm not sure should I define the head outside or inside, like
    typedef node ptr;
    ptr head;
    can you give me some example for how should I use the head pointer? thank you

  2. #2
    Green Member Cshot's Avatar
    Join Date
    Jun 2002
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    892
    Here's the tutorial on this site:
    http://www.cprogramming.com/tutorial/lesson15.html

    No, you shouldn't declare the head pointer there. It should go outside the structure. You don't want all of your structures to have a head pointer, just one global one to manipulate your list.
    Try not.
    Do or do not.
    There is no try.

    - Master Yoda

  3. #3
    Code Goddess Prelude's Avatar
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    9,796
    The most straightforward way is to declare two structures, one for each node in the list and one which contains an entire list by way of a head pointer.
    Code:
    struct link
    {
      void *data;
      struct link *next;
    };
    
    struct list
    {
      struct link *head;
      int n_links;
    };
    Now you simply create an instance of the list struct and add new nodes as usual to the head pointer.

    -Prelude
    My best code is written with the delete key.

  4. #4
    Visionary Philosopher Sayeh's Avatar
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    Aug 2002
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    212
    Where did this 'specialized' idea of a head pointer come from? that's not how it's normally done.

    Maybe you're confusing two separate issues-- linked lists and circular queues. 'Head' pointers aren't the same as 'root' node pointers, in conversation.

    Both can have head and tail pointers, but usually it's implemented like this:

    Code:
    For a circular queue:
    
    typedef struct
       {
       long                     data;
       long                     moreData;
       . . .
       }node,*nodeP;
    
    node      queue[10];
    nodeP    headPtr;
    nodeP    tailPtr;
    
    /* Create 10 nodes as an array         */
    
    
    headPtr = &queue[0];                    /* init head */
    tailPtr = &queue[0];                       /* init tail */
    
    /* as data is added to the queue, the
     * head pointer is incremented to the
     * next element.  If the head pointer
     * pointer ever == the tail (swallows
     * the tail), the queue is overrun/full
     * The idea is that something else is
     * following along, pulling data out of
     * the tailptr and incrementing it so
     * it tries to catch up (or run at the
     * same rate) with the headptr.  If
     * the tail catches up to the head
     * pointer, the queue is empty.
     */
    And for a linked list, like this:

    Code:
    typedef struct nodeStruc
       {
       struct nodeStruc *next;
       long                     data;
       long                     moreData;
       . . .
       }node,*nodeP;
    
    nodeP   nodeListP[10];
    
    /* allocate 10 (or however many needed) nodes
     * and link them together (or created and link them
     * as needed
     */
    
    nodeP headPtr;
    headPtr = nodeListP[0];
    I mean, in terms of 'head pointers', usually that mechanism is used only when working with an array or an array of structures.

    I hope this was not too far off what you were looking for.
    It is not the spoon that bends, it is you who bends around the spoon.

  5. #5
    Banned Troll_King's Avatar
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    Oct 2001
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    1,784
    Code:
    struct card_t
    {
    	int suit, face;
    };
    
    struct node_t
    {
    	struct node_t *next;
    	struct card_t card;
    	int size;
    };
    
    node_t * AddNode(node_t *);
    
    int main()
    {
    	//This is a pointer to the first node in the list
    	//and is used to reference the entire list
    	struct node_t *headp;
    
    	//add one node to the list
    	headp = AddNode(headp);
    	return 0;
    }
    
    node_t * AddNode(node_t *returnp) {  
    	node_t *newp;
    	//allocate space for new node
    	//fill new node with information
    	//add new node to the head of the list 
    	newp->next = returnp; 
    	//reassign the returned pointer to the head
    	returnp = newp;
    	//return the return pointer to the head
    	return returnp; 
    }
    The head pointer node is just used to reference the list. It is your only connection to a singly linked list and is the first node in the list.
    Last edited by Troll_King; 08-23-2002 at 10:45 AM.

  6. #6
    Ausandy
    Guest

    Smile head pointer

    Thanx, all ! And I still have a question on my case, for example, if I want to create a function which need to insert node into a linked list, which each node hodes a row header of another linked list, like a sparse matrix, I can declare the function prototype like void matrix(matrix *, int row_num, int col_num, int value), how should I define structrue, can I define like following?
    typedef struct row_header{
    struct dataNode *rowhead;
    struct row_header *next;
    int rowNum;
    }SparseMatrix;

    typedef SparseMatrix *rowHeaderPtr;

    typedef struct data_node{
    struct dataNode *next;
    float data;
    int colNum;
    }dataNode;
    thanks to give me a little comments!

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