C中的链表问题

Question

我必须生成随机数，并将它们放入排序的链表中。我的代码在cygwin上的家用电脑上运行得很好，但当我在学校系统上运行它时，我总是发现列表是空的。不确定问题出在哪里。

#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("nn");
    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
 }

Answer 1

您的函数

1. 具有未定义的行为，因为在某些情况下，它不返回任何内容，并且
2. 总的来说，您没有重新分配头dummy。所以它不是已更改

的功能如下

 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;  
}

该函数必须像一样调用

insertNodeSorted( &dummy, a );

Answer 2

既然是家庭作业，我不会给你完整的答案。。。。但是看看main的dummy发生了什么，以及insertNodeSorted中head的本地值。

如果您只是使用gcc而没有调试器。。。添加更多的printf会有很大帮助。。。