C：內存中的簡單鏈接列表訪問錯誤

Question

#include "List.h" 

typedef int element;         
typedef struct _ListNode //form of node 
{ 
    element data;          
    struct ListNode *link; 
} ListNode; 


ListNode *header = NULL; //make header in global variable 
int num_node = 0; //counting number of nodes 

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; 
    new_item = (ListNode *)malloc(sizeof(ListNode)); 

    if (new_item == NULL) return 0; 

    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;     
     } 
    } 
    num_node++;           
    return 1;           
} 


void DisplayItem(void) //print all the nodes 
{ 
    ListNode *current = NULL; 
    current = header; 
    while (current != NULL) 
    { 
     printf("%d\n", current->data); //MEMORY ACCESS PROBLEM 
     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)) 
    { 
     int current_position = 0;  
     current = header;   
     while (current_position != (position - 1)) 
     { 
      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;  
    DisplayItem(); 

    getchar(); 
    return 0; 
} 

我想製作簡單的鏈接列表程序。但由於內存訪問問題而無法工作。 此外，我做了兩個更多的節點，但它不會附加除了節點1. 我想使用Call-by-Reference。並且所有功能都應使結果爲0,1。

0 - fail. 
1 - success. 

它看起來很不舒服，但...我怎麼能做這個工作？

Answer 1

請參考下面用我的評論您簡單的錯誤，並與我校以下嘗試： -

typedef struct _ListNode //form of node 
{ 
    element data;          
    struct ListNode *link;/* here it should be _ListNode */ 
} ListNode; 

現在看到你做了錯誤

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

    if (new_item == NULL) return 0; 

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

    if (header == NULL)       
     header = new_item;      
    else{         
     current = header;      
     while (current->link != NULL) 
     /* here in the above while statement current->link always NULL because it is pointing to the first node and first->next == NULL. Hence this while loop will never execute and link list will not be created because you have assign the new node inside this while loop. Move the code out side of this loop */    
     { 
      current = current->link;      
      current->link = new_item;     
     } 
    } 

正確的以下方法while循環應該是

 while (current->link != NULL) 
     { 
      current = current->link;         
     } 
      current->link = new_item; /* this line of code should be out side of while loop */ 
    num_node++;           
    return 1;           
} 

Just correct the while loop like above in function AppendNode as well. 
Now it will work fine