C语言链表中间插入、遍历显示、指定位置删除功能异常

异常现象 #

• 异常1：依次调用头插addAtfront、尾插addAtback、位置2插入addInbetween函数时，输入完中间节点名称后程序直接终止，无法执行后续显示、删除逻辑，异常输出如下：

--------------------------------
-----------Cake Shop------------
--------------------------------
First cake: First
Second cake : Second
Between cake : Between


...Program finished with exit code 0
Press ENTER to exit console.

• 异常2：额外增加一次addAtfront、addAtback调用后，程序可运行至显示、删除流程，但中间插入节点位置错误，删除非头节点时会出现链表节点丢失错位问题，异常输出如下：

--------------------------------
-----------Cake Shop------------
--------------------------------
First cake: First1
First cake: First2
Second cake : Second1
Second cake : Second2
Between cake : Middle
List of cakes
First2
First1
Second1
Second2
Middle

Deleting cake at position 1: 
Present of now:
List of cakes
First1
Second1
Second2
Middle

问题根因 #

所有异常均来自3个核心功能函数的逻辑错误：

1. 中间插入函数addInbetween遍历逻辑错误
   • 循环终止条件写为count<=pos，比正确遍历逻辑多走1个节点：当链表仅2个节点（头+尾）时，遍历结束后指针zig会走到NULL位置，后续执行zig->next直接触发空指针解引用，导致程序崩溃，是第一个异常的直接原因
   • 即使链表长度足够不触发崩溃，多走1步也会让插入位置偏移1位，直接把新节点插到目标位置的后方，甚至链表尾部，对应第二个异常里中间节点出现在链表最后的问题
2. 删除函数delete逻辑错误
   • 空链表判断逻辑错误：判断条件写为head == NULL，但head是传入的二级指针（存储头指针变量的地址），永远不会为空，正确判断应该是*head == NULL
   • 非头节点删除时断链：找到待删除节点后，直接将前驱节点的next设为NULL，没有连接待删除节点的后继节点，导致待删除节点后的所有节点全部丢失，引发链表错位
3. 打印函数display格式错误
   • 表头字符串List of cakes写在循环内部，每打印一个节点就会重复输出一次表头
   • 节点名称输出后未加换行，所有内容会挤在同一行，格式混乱

修复后完整代码 #

#include <stdio.h>
#include <stdlib.h>
struct FlavorList{
    char name[100];
    struct FlavorList* next ; 
};

void addAtfront(struct FlavorList **head){
    struct FlavorList *new_cake = (struct FlavorList*)malloc(sizeof(struct FlavorList));
    printf("First cake: ");
    scanf("%s",new_cake->name);
    new_cake->next = *head ; 
    *head = new_cake ; 
}

void addAtback(struct FlavorList **head){
    struct FlavorList* new_cake = (struct FlavorList*) malloc(sizeof(struct FlavorList)); 
    printf("Second cake : ");
    scanf("%s",new_cake->name);
    new_cake->next = NULL;
    struct FlavorList *last = *head;  
    if (*head == NULL){
       *head = new_cake;
       return;    
    } 
    while (last->next != NULL)
        last = last->next;
    last->next = new_cake;
    return;   
}

void addInbetween(struct FlavorList  ** head , int pos){
    struct FlavorList * new_cake = (struct FlavorList *) malloc(sizeof(struct FlavorList ));
    printf("Between cake : ");
    scanf("%s",new_cake->name);
    new_cake->next = NULL;
    // 位置合法性判断
    if(pos < 1){
        free(new_cake);
        printf("Invalid position\n");
        return;
    }
    // 插入位置为1直接复用头插逻辑
    if(pos == 1){
        new_cake->next = *head;
        *head = new_cake;
        return;
    }
    struct FlavorList  *zig = *head ; 
    int count = 1 ; 
    // 遍历到待插入位置的前驱节点（第pos-1个节点）即停止
    while(zig!=NULL && count < pos-1){
        count ++ ; 
        zig=zig->next ; 
    }
    // 位置超出链表长度容错处理
    if(zig == NULL){
        free(new_cake);
        printf("Position out of range, add to back\n");
        addAtback(head);
        return;
    }
    new_cake->next = zig->next ; 
    zig->next = new_cake ; 
}

void delete(struct FlavorList **head, int pos){
    // 正确判断空链表
    if(*head == NULL){
        printf("List is empty");
        return;
    }
    struct FlavorList*current=*head;
    struct FlavorList*previous=*head;
    if (pos==1){
        *head=current->next;
        free(current);
        current=NULL;
    }
    else{
        while(pos!=1){
            previous=current;
            current=current->next;
            pos--;
            // 位置越界容错
            if(current == NULL){
                printf("Position out of range\n");
                return;
            }
        }
        // 连接后继节点，避免断链
        previous->next=current->next;
        free(current);
        current=NULL;
    }
}

void display(struct FlavorList  **head){
    struct FlavorList  *zig = * head ;
    printf("List of cakes\n");
    while(zig != NULL){
        printf("%s\n",zig->name);
        zig=zig->next; 
    }
    printf("\n");
}

int main(){
    struct FlavorList *head = NULL ; 
    printf("--------------------------------\n");
    printf("-----------Cake Shop------------\n");
    printf("--------------------------------\n");
    addAtfront(&head);
    addAtback(&head);
    addInbetween(&head,2);
    display(&head);
    printf("Deleting cake at position 1: \n");
    delete(&head,1);
    printf("Present of now:\n");
    display(&head);
    return 0;
}

修复验证 #

第一个测试场景（头插+尾插+位置2插入）运行输出符合预期：

--------------------------------
-----------Cake Shop------------
--------------------------------
First cake: First
Second cake : Second
Between cake : Between
List of cakes
First
Between
Second

Deleting cake at position 1: 
Present of now:
List of cakes
Between
Second

内容的提问来源于stack exchange，提问作者Sahayog Shrestha