c - C中的简单链表(2): Trash result

Question

我再问一个问题。非常抱歉打扰大家。

事实上，我破解了 Memory Access Problem 。但我无法理解执行的结果。

来源就在这里。

/*
    https://stackoverflow.com/questions/46602732/simple-linked-list-in-c-memory-access-error
*/

#include "List.h" //main.h and stdlib.h


typedef int element;                                    
typedef struct _ListNode //define the form of Node                              
{
    element data;                               
    struct _ListNode *link;                         
}   ListNode;


ListNode *header = NULL; //header node is global
int num_node = 0; //node-counting

//define function
int AppendNode(const ListNode item);                
void DisplayItem(void);                     
int InsertNode(const int pos, const ListNode item);     


int AppendNode(const ListNode item)                     
{
    ListNode *current, *new_item = NULL; //'current' for searching. 'new_item' for Appending
    new_item = (ListNode *)malloc(sizeof(ListNode));

    if (new_item == NULL)   return 0; //fail for Dynamic Allocation

    new_item->data = item.data; 
    new_item->link = NULL;  

    if (header == NULL)
        header = new_item;                      
    else{                                   
        current = header;                       
        while (current->link != NULL)                   
            current = current->link;                
        current->link = new_item; //BUSTED!
    }
    num_node++;                                         
    return 1;                                           
}


void DisplayItem(void)
{
    ListNode *current = NULL;
    current = header;   
    while (current != NULL) 
    {
        printf("%d\n", current->data);              
        current = current->link;                
    }
}



int InsertNode(const int position, const ListNode item)
{
    ListNode *current = NULL;
    ListNode *new_item = NULL;              
    new_item = (ListNode *)malloc(sizeof(ListNode));    

    if (new_item == NULL)   return 0;

    if (position == 1)                          
    {
        new_item->link = header;                        
        header = new_item;                          
        num_node++;                             
    }
    else if((1 < position) && (position <= (num_node+1)))   
    {
        int current_position = 0;                       
        current = header;                           
        while (current_position != (position - 2))      
        {
            current = current->link;
            current_position++;
        }
        new_item->link = current->link;                 
        current->link = new_item;                   
        num_node++;                         
    }
    else return 0;
}


int main(void)
{
    ListNode node1; node1.data = 10;
    ListNode node2; node2.data = 20;
    ListNode node3; node3.data = 40;
    ListNode node4; node4.data = 50;
    ListNode node5; node5.data = 60;

    AppendNode(node1);
    AppendNode(node2);
    AppendNode(node3);
    AppendNode(node4);
    AppendNode(node5);

    DisplayItem();

    printf("========================\n");

    ListNode insert; insert.data = 30;
    InsertNode(3,insert);
    DisplayItem();

    getchar();
    return 0;
}

该来源的结果是

10
20
40
50
60
========================
10
20
8476480
40
50
60

InsertNode(3,insert); 之后的第三个节点是垃圾。

首先我认为这可能是一个逻辑问题，我首先编写了伪代码。所以我查了一下，但很清楚。

第二我以为可能是我的电脑问题，但绝对不是。

最后我认为这可能是节点计数过程的问题，但它工作得很清楚。

我应该如何完成这项工作？

Answer 1

您没有将 item.data 等同于 new_item->data :

int InsertNode(const int position, const ListNode item)
{
    ListNode *current = NULL;
    ListNode *new_item = NULL;              
    new_item = (ListNode *)malloc(sizeof(ListNode));    
    current = (ListNode *)malloc(sizeof(ListNode)); 
    new_item->data = item.data; //This line is not present in your code

    if (new_item == NULL)   return 0;

    if (position == 1)                          
    {
        new_item->link = header;                        
        header = new_item;                          
        num_node++;                             
    }
    else if((1 < position) && (position <= (num_node+1)))   
    {
        int current_position = 0;                       
        current = header;                           
        while (current_position != (position - 2))      
        {
            current = current->link;
            current_position++;
        }
        new_item->link = current->link;                 
        current->link = new_item;                   
        num_node++;                         
    }
    else return 0;
}

下次提问之前请考虑使用调试器。希望对您有所帮助。