在单个链接列表的前面添加节点后，我无法在每个节点中遍历。

Question

我遇到了一个Node的问题，在列表前添加新的节点后，无法遍历Node列表。在列表前添加新节点后，我无法遍历Node列表。添加的结果不是动作。除非我把函数 "Add_a_another_Node_in_first_list "的主体放在函数main里面，否则就可以了。谁能给我解释一下为什么？

#include<iostream>
using namespace std;
struct LinkedList
{
    int data;
    struct LinkedList *pnext;

}; typedef struct LinkedList Node;

void Create_a_Node(int data, Node *head)
{
    head->data = data;
    head->pnext = NULL;
}
void Add_a_Node_in_first_list(Node *second, Node *head, Node *third)
{
    head->pnext = second;
    head->data = 0;
    second->data = 1;
    second->pnext = third;
    third->data = 2;
    third->pnext = NULL;
}

void Add_a_another_Node_in_first_list(int data, Node *head)
{
    Node *new_node = new Node;
    new_node->data = data;
    new_node->pnext = head;
    head=new_node;

}
void Traversal_Nodes(Node *ptr)
{
    while (ptr != NULL)
    {
        cout << ptr->data << "\t" << ptr;
        cout << endl;
        ptr = ptr->pnext;
    }

}
int main()
{
    Node *head = NULL;
    Node *second = NULL;
    Node *third = NULL;
    head = new Node;
    second = new Node;
    third = new Node;
    Create_a_Node(1, head);
    Add_a_Node_in_first_list(second,head, third);
    Traversal_Nodes(head);
    Add_a_another_Node_in_first_list(-1, head);
    cout << "\nAfterwards\n";
    Traversal_Nodes(head);

} 

Answer 1

当调用这个函数时 Add_a_another_Node_in_first_list()的值，你正在改变 head. 因此传递头指针的引用。

请看下面的实现。

#include<iostream>
using namespace std;
struct LinkedList
{
    int data;
    struct LinkedList *pnext;

}; typedef struct LinkedList Node;

void Create_a_Node(int data, Node *head)
{
    head->data = data;
    head->pnext = NULL;
}
void Add_a_Node_in_first_list(Node *second, Node *head, Node *third)
{
    head->pnext = second;
    head->data = 0;
    second->data = 1;
    second->pnext = third;
    third->data = 2;
    third->pnext = NULL;
}

void Add_a_another_Node_in_first_list(int data, Node* *head)
{
    Node* new_node = new Node;
    new_node->data = data;
    new_node->pnext = *head;
    *head=new_node;

}
void Traversal_Nodes(Node *ptr)
{
    while (ptr != NULL)
    {
        cout << ptr->data << "\t" << ptr;
        cout << endl;
        ptr = ptr->pnext;
    }

}
int main()
{
    Node *head = NULL;
    Node *second = NULL;
    Node *third = NULL;
    head = new Node;
    second = new Node;
    third = new Node;
    Create_a_Node(1, head);
    Add_a_Node_in_first_list(second,head, third);
    Traversal_Nodes(head);
    Add_a_another_Node_in_first_list(-1, &head);
    cout << "\nAfterwards\n";
    Traversal_Nodes(head);

} 

输出：

0    0x171e670
1    0x171e5b0
2    0x171e4d0

Afterwards
-1    0x171e410
0    0x171e670
1    0x171e5b0
2    0x171e4d0