Linked list issue in C | 易学教程

问题

I have to generate random numbers and put them in a linked list sorted. my code runs fine on my home computer on cygwin, however when I run it on the schools system, i keep getting that the list is empty. Not sure what the issue is.

#include<stdio.h>
#include<stdlib.h>

typedef struct node{
    int num;
    struct node *next;
}node_t;

node_t* insertNodeSorted(node_t *head, int x);
void printList(node_t *head);
void deleteList(node_t *head);

int main(int argc, char *argv[])
{
    node_t *dummy;
    int counter = 1;
    int a;

    if(argc != 4)
    {
            printf("Error. Exiting program...");
            exit(1);
    }//end if

    //seed random number
    srandom(atoi(argv[1]));
    dummy = NULL;

    while(counter < atoi(argv[2]))
    {
            a = random() % (atoi(argv[3]) + 1);

            printf("%d " ,a);

            insertNodeSorted(dummy, a);

            counter++;
    }//end while

    printf("\n\n");
    printList(dummy);

    deleteList(dummy);

    return 0;



 }

 node_t* insertNodeSorted(node_t *head, int x)
 {
    if(head == NULL)
    {
            head = (node_t *)malloc(sizeof(node_t));
            if(head == NULL)
            {
                    printf("Failed to create head node");
                    return head;
            }//end if
    head->num = x;
    head->next = NULL;
    return head;
    }//end if

    node_t *p;

    p = (node_t*)malloc(sizeof(node_t));
    if(p == NULL)
    {
            printf("Failed to create a new node.");
            return p;
    }//end if

    p->num = x;
    p->next = NULL;

    if(x < head->num)
    {
            p->next = head;
            return p;
    }//end if

    node_t *q, *r;
    q = head;
    while(q != NULL && q->num <= x)
    {
            r = q;
            q = q->next;
    }//end while
    p->next = q;
    r->next = p;

 }

 void printList(node_t *head)
 {
    node_t *p;

    if(head == NULL)
    {
            printf("List is empty");
            exit(1);
    }//end if

    p = head->next;
    while(p != NULL)
    {
            printf("%d ",p->num);
            p = p->next;
    }//end while
 }

 void deleteList(node_t *head)
 {
    node_t *p;
    while(p != NULL)
    {
            p = head->next;
            free(head);
            head = p;
    }//end while
 }

回答1:

Your function

has undefined behaviour because in some cases it returns nothing and
in the main you did not reassign the head dummy. So it is not changed.

The function can look the following way

 node_t* insertNodeSorted( node_t **head, int x )
 {
    node_t *p = ( node_t * )malloc( sizeof( node_t ) );

    if ( p == NULL )
    {
            printf( "Failed to create a new node.\n" );
    }//end if

    else
    {  
        p->num = x;

        if ( *head == NULL || x < ( *head )->num )
        {
            p->next = *head;
            *head = p;
        }
        else
        {
            node_t *current = *head;
            while ( current->next != NULL && !( x < current->next->num ) )
            {
                current = current->next;
            }

            p->next = current->next;
            current->next = p;
        }
    }

    return p;  
}

And the function must be called like

insertNodeSorted( &dummy, a );

回答2:

Since it's homework I will not give you the full answer.... but look at what is going on with main's dummy, and the local value of head inside insertNodeSorted.

If you are just using gcc and no debugger... add more printfs it'll help a ton...

来源：https://stackoverflow.com/questions/33525014/linked-list-issue-in-c

标签

linked-list