Thread: Problem in link list

  1. #1
    Registered User
    Join Date
    Jan 2007

    Problem in link list


    I have create a simple program for displaying a link list,but it is not working properly.
    The code is as follow:
    struct linklist
     int data;
     struct linklist *next;
    struct linklist *ptr;
    void insert(linklist *ptr)
        printf("INSIDE INSERT%u",ptr );
        int num; 
        struct linklist *temp = ptr;
        struct linklist *node = (struct linklist *)malloc(sizeof(struct linklist));
        printf("\n Enter the data \n");
        node->data = num;
        if ( ptr == NULL ) {
            printf("INSIDE IF%u",ptr );
            ptr = node;
            node->next = NULL;
        else {
            printf("INSIDE ELSE"); 
            while ( temp->next != NULL ) {
                temp = temp->next;
            temp->next = node;
            node->next = NULL;
    void display(linklist *ptr) 
        struct linklist *temp = ptr;
        while ( temp != NULL ) {
            printf("%d",temp->data );
            temp = temp->next; 
    int main()
     ptr = NULL; 
        int ch;
        while ( 1 ) {
          switch ( ch ) {
              case 1:
              case 2:
              case 3:
       printf("\nEnter your choice ");
    The problem is that in insert(ptr) function it always showing the ptr value 0 i.e NULL which I don't understand since the ptr I have declared as global so it should not be initialized to 0 every time the loop runs.
    Can anybody explain me the behavior and solution to it.


  2. #2
    Ugly C Lover audinue's Avatar
    Join Date
    Jun 2008
    ptr should be allocated first...

  3. #3
    Algorithm Dissector iMalc's Avatar
    Join Date
    Dec 2005
    New Zealand
    Pointers themselves are passed by value. your global ptr is not modified by passing it to insert. To do that you'd need to either return ptr as well or prototype the function to take a pointer to a pointer, and pass it that.
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