c - 我不明白deleteall(key)函数中这条语句 "cur = prev->next;"的逻辑

Question

该程序创建一个在开头插入的链表，并具有一个 deleteall(key) 函数，该函数将删除具有该键值的所有节点

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

struct node{

    int data;
    struct node* next; //creation a linked list with insertion at beginning
};

struct node* head = NULL;
int totaldeleted = 0;


void create(n) {

    int i;
    struct node *newnode, *temp;
    newnode = (struct node*)malloc(sizeof(struct node));
    printf("Enter the data: ");
    scanf("%d", &newnode -> data);
    newnode -> next = NULL;

    if(head==NULL){
        head=newnode;    
    }

    temp = head;
    for(i=2; i<=n; i++){
        int data;
        newnode = (struct node*)malloc(sizeof(struct node));
        printf("Enter the data: ");
        scanf("%d", &data);

        newnode -> data = data;
        newnode -> next = NULL;

        newnode -> next = head;
        head = newnode;
    }
}

void display(){

    struct node* temp;
    printf("\nThe Linked list is: ");
    temp = head;

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

}

int deleteall(key){ 

    struct node *prev, *cur;
    if(head == NULL){
        prev = NULL;
        cur = NULL;
        printf("\nList is empty!");
    }

    while(head != NULL && head->data == key){
        prev = head;
        head = head -> next;
        free(prev);
        totaldeleted++;   

    }
    prev = NULL;
    cur = head;

    while(cur != NULL){

        if(cur->data == key && prev != NULL){
               prev -> next = cur->next;
               free(cur);
               cur = prev->next; // I cannot understand this logic.
               totaldeleted++;
        }
        else {

         prev = cur;
        cur = cur -> next;

        }
    }
    return totaldeleted;
}

int main(){
    int n, key;

    printf("Enter the number of nodes: ");
    scanf("%d", &n);

    create(n);
    display();
    printf("\nEnter the key: ");
    scanf("%d", &key);
    totaldeleted = deleteall(key); 
    printf("Total deleted: %d", totaldeleted);
    display();

    printf("\n");

}

Answer 1

就在该行之前，cur 指向已删除节点 - 该节点现已释放，因此 cur 指针的值不确定。我们希望将 cur 指向已删除节点后面的节点。如果它没有被删除，我们可以从cur->next获取它。但是，cur->next 无效。我们可以在 free...

之前使用一个临时变量来存储 cur->next 的值

但是，在free之前有这样一行:

prev -> next = cur->next;

即现在我们需要的值已经分配到了 prev->next 中，因此我们不需要临时变量，但可以从 prev->next 中获取它。