C - 鏈表：這個函數應該輸出什麼？

Question

我堅持着這片代碼，我在考試的模擬發現：

struct node{ 
    int val; 
    struct node* next; 
}; 

struct node* list; 

struct node* function (struct node* p){ 
     struct node *temp, *prec = NULL; 
     if (p!=NULL){ 
      while(p->next!=NULL){ 
       temp=prec; 
       prec=p; 
       p=p->next; 
       prec->next=temp; 
       } 
       p->next=prec; 
     } 
     return p; 
    } 

我試着編譯它，顯示的輸出是一個反向列表。例如：如果我的列表由1,2,3和4組成。顯示的輸出是4,3,2和1.我的問題是：有人能解釋我在while循環內發生了什麼嗎？

Answer 1

我改名變量，使事情更清晰：

struct node* function (struct node* current_node){ 
    struct node *temp;    
    struct node *previous_node = NULL; 
    if (current_node!=NULL){ 
    while(current_node->next!=NULL){ 
     temp    = previous_node;  //Save pointer to upstream node 
     previous_node  = current_node;  //Make previous node the current node 
     current_node  = current_node->next; //Move to the next node 
     previous_node->next = temp;    //Set the previous node to point to the previous previous node 
    } 
    current_node->next=previous_node;   //Set final node to point to last previous node 
    } 
    return current_node; 
}