c - 反向打印双向链表

Question

我有一个可以从上到下打印的双向链表，现在我正尝试从下到上打印它。

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

//defines the struct UserData
typedef struct
{
    int importance;
    char taskName[80];
}UserData, *UserDataPtr;

//Defines a node
typedef struct node {
    UserData Data;
    struct node *next;
    struct node *prev;
    } Node, *NodePtr;

NodePtr makeNode(UserData);

//Declare function printList
void printList(NodePtr);

void printListRev(NodePtr);

int main()
{
   UserData info;
   NodePtr top, ptr, last, temp;



   top = NULL;

    FILE *filein=fopen("Data.txt", "r");
    if (filein == NULL) {
        printf("Error opening file, exiting program.\n");
        exit(0);
    }

    while(fscanf(filein, "%d%s",&info.importance, info.taskName)==2)
        {
            ptr=makeNode(info);
            if (top == NULL) top = ptr;
            else last -> next = ptr;
            last = ptr;
        }//end while loop

    printList(top);


    printListRev(last);
   }//end Main


//printList is a function that prints each node as long as it isn't NULL. Once it reaches NULL it terminates, signifying the end of the list.
void printList(NodePtr ptr) {
    while (ptr != NULL) { //as long as there's a node
            printf("%d %s\n", ptr -> Data.importance, ptr -> Data.taskName);
            ptr = ptr -> next; //go on to the next node

        }
    if (ptr == NULL) {

        printf("Last node data printed moving forward.\n");
    }

    } //end printList


void printListRev(NodePtr ptr) {
    while(ptr != NULL){
        printf("%d %s\n", ptr -> Data.importance, ptr -> Data.taskName);
        ptr = ptr -> prev;


      }
    }//end printListRev

//Define function makeNode. Allocates storage for node, stores integer given to it, and returns a pointer to the new node. Also sets next field to NULL
NodePtr makeNode(UserData info) {
    NodePtr ptr = (NodePtr) malloc(sizeof (Node));
    ptr -> Data = info;
    ptr -> next = NULL;
    ptr -> prev = NULL;
    return ptr;
} //End makeNode

这是输出:

1 task1
2 task2A
3 task3A
2 task2B
4 task4A
4 task4B
3 task3B
Last node data printed moving forward.
3 task3B

而且我不知道为什么它不会反向打印完整列表。反向打印时只打印一项。

直到“打印的最后一个节点数据”消息都是正确的。是的，它有点乱，我是 C 的新手，我需要清理我的评论等等。抱歉。

有人能帮忙吗？

Answer 1

将节点插入列表时，您忘记将 prev 字段设置为适当的值。修复很简单:将 last 初始化为 NULL，然后在 ptr = makeNode(信息);

顺便说一下，temp 没有被使用。