C: 链表内存访问错误

Question

我必须处理链表，甚至在main中发生某些事情之前，我就会遇到一个严重的访问错误。我不知道怎么了。我对动态内存管理比较陌生。如果有人能看一下功能就好了。申报单是由教授出具的，所以我们必须退回一张DoubleNote*。我的代码如下：

#include <stdio.h>
#include <stdlib.h>
typedef struct node{
    double var;
    struct node *next;

} DoubleNode;

DoubleNode* insertFirst(DoubleNode* head, double d){
    DoubleNode* new_head;
    new_head = (DoubleNode*)malloc(sizeof(DoubleNode));
    if (new_head == NULL) {
        printf("Error: Allocating memory for new node failed!");
        exit(1);
    }
    new_head->var = d;
    new_head->next = head;
    head = new_head;

    return head;
}

DoubleNode* inserLast(DoubleNode* head, double d){
    DoubleNode* current = head;
    while (current != NULL) {
        current = current->next;
    }
    current->next = (DoubleNode*)malloc(sizeof(DoubleNode));
    if (current->next == NULL) {
        printf("Error: Allocating memory for new node failed!");
        exit(1);
    }
    current->next->var = d;
    current->next->next = NULL;
    return head;
}
DoubleNode* inverseDoubleListCon(DoubleNode* head){
    DoubleNode* current = head; // iteration variable starts on head of old list
    DoubleNode* conHead = current; // Head of the new list
    while (current != NULL) {
        current = current->next; //iteration step
        DoubleNode* newConHead = (DoubleNode*)malloc(sizeof(DoubleNode)); //allocating memory for new head
        if (newConHead == NULL) {
            printf("Error: Allocating memory for new node failed!");
            exit(1);
        }
        newConHead = current; // new_head is the next variable in the old list
        newConHead->next = conHead; //new head points to old head of the new list
        conHead = newConHead; // new head is set
    }

    return conHead;
}
void printList(DoubleNode* head){
    DoubleNode* current = head;
    while (current != NULL) {
        printf("%lfn", current->var);
        current = current->next;
    }
}


int main(){
    DoubleNode* head = NULL;
    DoubleNode* inverseHead = NULL;
    double d;
    int i;
    int sizeOfList;
    printf("Insert amount of variables: n");
    scanf("%d", &sizeOfList);
    for (i = 0; i < sizeOfList; i++) {
        printf("Insert variable for node [%d]: n", i);
        scanf("%lf", &d);
        head = insertFirst(head, d);
    }
    printList(head);
    inverseHead = inverseDoubleListCon(head);
    printList(inverseHead);

    return 0;
}

Answer 1

首先未初始化sizeOfList。您需要添加代码来从用户那里获取大小的值。

您也不会从insertFirst函数更新头指针的值。下面的代码应该会有所帮助。

DoubleNode* head= NULL;
// Code to get the value of sizeofList
for (i = 0; i < sizeOfList; i++)
{
   ...
    head = insertFirst(head, d);
}

反向函数过于复杂。您正在newConHead中分配内存，这对于反转链表是不需要的。

我建议按照"如何仅使用两个指针反转单链表？或http://www.geeksforgeeks.org/write-a-function-to-reverse-the-nodes-of-a-linked-list/