C 链表函数程序遇到段错误

Question

我有一个作业要编写一些处理链表的函数。其功能是:insertFront - 将一个新节点放在列表的前面

insertBack - 将新节点放在列表末尾

print - 打印当前链表

Max - 返回列表中的最大值

Min - 返回列表中的最小值

locInList - 返回列表中的位置编号

我已经完成了我的代码，我认为它会起作用，但我一直遇到段错误。我知道这意味着我正在尝试访问不存在的内存部分。我不明白我做错了什么。

我尝试过分离和注释掉函数，看起来程序运行良好，直到我点击打印函数。打印函数没有按应有的方式打印，我假设段错误发生在我的 max min 和 locInList 函数中。编译器没有错误消息。

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

struct node
{
        int data;
        struct node *next;
};
typedef struct node node;

node* insertFront(node* head, int d);
node* insertBack(node* head, int d);
void print(node* head);
int max(node* head);
int min(node* head);
int locInList(node* head, int x);

int main()
{
        node* head = NULL;

        head = insertFront(head, 5);
        head = insertFront(head, 4);
        head = insertBack(head, 6);
        head = insertBack(head, 7);
        print(head);

        printf("Max: %d\n", max(head));
        printf("Min: %d\n", min(head));
        printf("locInList 5: %d\n", locInList(head, 5));
        printf("locInList 9: %d\n", locInList(head, 9));
   return 0;
}

node* insertFront(node* head, int d)
{
        node *tmp = NULL;
        tmp = malloc(sizeof(node));
        tmp->data = d;
        tmp->next = head;
        head = tmp;


        return head;
}

node* insertBack(node* head, int d)
{
    node *tmp = malloc(sizeof(node));

    tmp->data = d;
    tmp->next = NULL;

    if(head == NULL) return tmp;

    node *end = head;

    while(end->next != NULL){
    end = end->next;
    }
    end->next = tmp;


    return head;


}

void print(node* head)
    {

        node *tmp = head;

        while(tmp != NULL){
        printf("%d ", tmp->data);
        tmp = tmp->next;
                        }
}

int max (node* head)
{
        int max = 0;
        node *tmp = NULL;

        tmp = head;

        while(tmp->next != NULL){
                if(tmp->data >= max){
                max = tmp->data;
                tmp = tmp->next;
                           }
                           }

        return max;                             
}

int min (node* head)
{
        int min = head->data;
        node *tmp = NULL;

        tmp = head;

        while(tmp != NULL){
        if(tmp->data <= min){
                min = tmp->data;
                tmp = tmp->next;
                        }
                        } 

        return min;
}

int locInList(node* head, int x)
{

        int i = 0;
        node *tmp = NULL;

        tmp = head;

        while(tmp != NULL){


                if(tmp->data == x){
                     return i;
                }else{
                     i++;
                     tmp = tmp->next;

                        }  
                        }
                return i;

}

Answer 1

您的代码中有几个错误，但这里有一个很容易开始的错误:

node* insertFront(node* head, int d)
{
        node *tmp = NULL;
        tmp = malloc(sizeof(node));
        tmp->data = d;
        tmp->next = head;
        return head;   // Sure you want to return head ?
                       // The first time you call this function head is NULL
                       // and then you return NULL
                       // How about returning tmp instead
}

现在有一个更复杂的错误:

node* insertBack(node* head, int d)
{
        node *tmp = NULL;
        node *end = head;
        tmp = malloc(sizeof(node));  // Why malloc two new nodes ?
        end = malloc(sizeof(node));  // Your code shall only insert one new node
        tmp->data = d;
        tmp->next = NULL;

        while(end->next != NULL){
            end = end->next;
            end->next = tmp;  // Here you destroy the list by inserting
                              // the new node in incorrect places.
                              // You don't want to do this until
                              // the end has been reached
                      }

        return head;  // Again ... this is bad when called the first time
}

试试这个:

node* insertBack(node* head, int d)
{
        node *tmp = malloc(sizeof(node));
        tmp->data = d;
        tmp->next = NULL;
        if (head == NULL) return tmp;

        node *end = head;

        while(end->next != NULL){
            end = end->next;
        }
        end->next = tmp;

        return head;
}

在函数 max、min 和 locInList 中，您有一个不必要的 tmp = malloc(sizeof(node)); 这会导致内存泄漏。