Question

我试图做一个程序，从链接列表中插入和删除学生，当我尝试在列表的末尾插入一个学生，但它没有工作。我觉得我的功能算法是正确的，但我仍然。无论如何，这里是代码：

void InsetEnd(){

stud *temp, *newnode;   
char n[15];
int a;

printf("Student: \n");
printf("Name: ");
scanf("%s", n);
printf("Age: ");
scanf("%d", &a);

strcpy(newnode->name, n);
newnode->age=a;

temp=head;

while(temp!=NULL){
    temp=temp->next;
}
temp = (stud *) malloc (sizeof(stud));

newnode->next = NULL;   
temp->next = newnode; }

Answer 1

对于初学者，指针newnode具有不确定的值。因此这些陈述

strcpy(newnode->name, n);
newnode->age=a;

导致未定义的行为。

此循环

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

没有意义，因为很明显，在循环之后，指针temp将等于NULL。

您必须更改列表中的最后一个指针，然后插入新节点。

该函数至少可以通过以下方式查看（尽管使用带有字符数组的函数scanf，因为它在您的程序中使用是不安全的）

void InsetEnd()
{
    stud *newnode;
    stud **temp;   
    char n[15];
    int a;

    printf("Student: \n");
    printf("Name: ");
    scanf("%s", n);
    printf("Age: ");
    scanf("%d", &a);

    newnode = ( stud * )malloc( sizeof( stud ) );

    strcpy( newnode->name, n );
    newnode->age = a;
    newnode->next = NULL;

    temp = &head;

    while ( *temp != NULL ) temp = &( *temp )->next;

    *temp = newnode;
}

Answer 2

我能够解决问题。它只是函数中的分配位置。我实际上必须在创建节点之前分配内存，如果你反转它不会创建任何东西，它只会显示垃圾。

void InsetEnd(){

stud *temp, *newnode;   
char n[15];
int a;

printf("Student: \n");
printf("Name: ");
scanf("%s", n);
printf("Age: ");
scanf("%d", &a);

newnode = (stud *) malloc (sizeof(stud));
strcpy(newnode->name, n);
newnode->age=a;

temp=head;

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

newnode->next = NULL;
temp->next = newnode;   }

Answer 3

好像你抓住了自己的问题。在尝试访问或设置数据之前分配内存至关重要！我觉得还有一些事情需要提及，以便将来帮助你。

void InsetEnd(stud *head) { // pass head pointer, becomes local pointer so its not overriden
    if (!head) 
        return; // dont do anything if list does not exist

    stud *newnode; // no need for tmp anymore
    char n[15] = ""; // initialize
    int a;

    printf("Student: \n");
    printf("Name: ");
    scanf("%14s", n); // take only 14 chars, leaving the 15th '\0' or you'll have problems reading long names after
    printf("Age: ");
    scanf("%d", &a);

    newnode = calloc(1,sizeof(*newnode)); // use calloc to avoid junk
    // ^ type casting a return of void* is not necessary in c

    strcpy(newnode->name, n);
    newnode->age=a;

    while(head->next) // NULL is pretty much false
        head=head->next;

    // no need to set newnode next to null, its already null from calloc
    head->next = newnode;   
}

希望这有帮助！

Answer 4

我将尝试从以下示例中解释它

  #include <iostream>

    /* run this program using the console pauser or add your own getch, system("pause") or input loop */
    class Node {
    public:
        double  data;       // data
        Node*   next;       // pointer
    };

    class List {
    public:
        List(void) { head = NULL; } // constructor
        ~List(void);                // destructor

        bool IsEmpty() { return head == NULL; } //boş kontrolü
        Node* InsertNode(int index, double x);  //node ekle
        int FindNode(double x);  //node bul
        int DeleteNode(double x); //node sil
        void DisplayList(void); //liste görüntüle
    private:
        Node* head; //baş kısmı
    };

    Node* List::InsertNode(int index, double x) {

        if (index < 0) return NULL; 

        int currIndex   =   1;
        Node* currNode  =   head;
        while (currNode && index > currIndex) {
            currNode    =   currNode->next;
            currIndex++;
        }
        if (index > 0 && currNode == NULL) return NULL;

        Node* newNode   =   new Node;
        newNode->data   =   x;  
        if (index == 0) {
            newNode->next   =   head;
            head        =   newNode;
        }
        else{
            newNode->next   =   currNode->next;
            currNode->next  =   newNode;
        }
        return newNode;
    }


    int List::FindNode(double x) {
        Node* currNode  =   head;
        int currIndex   =   1;
        while (currNode && currNode->data != x) {
            currNode    =   currNode->next;
            currIndex++;
        }
        if (currNode) return currIndex;
        return 0;
    }
    int List::DeleteNode(double x) {
        Node* prevNode  =   NULL;
        Node* currNode  =   head;
        int currIndex   =   1;
        while (currNode && currNode->data != x) {
            prevNode    =   currNode;
            currNode    =   currNode->next;
            currIndex++;
        }
        if (currNode) {
            if (prevNode) {
                prevNode->next  =   currNode->next;
                delete currNode;
            }
            else {
                head        =   currNode->next;
                delete currNode;
            }
            return currIndex;
        }
        return 0;
    }

    void List::DisplayList()
    {
       int num      =   0;
       Node* currNode   =   head;
       while (currNode != NULL)
       {
        printf("\n%lf",currNode->data);

        currNode    =   currNode->next;
        num++;
       }
       printf("\nNumber of nodes in the list: %d",num);
    }
    List::~List(void) {
       Node* currNode = head, *nextNode = NULL;
       while (currNode != NULL)
       {
        nextNode    =   currNode->next;
        // destroy the current node
        delete currNode;    
        currNode    =   nextNode;
       }
    }

    int main(int argc, char** argv) {

        List list;
        list.InsertNode(0,5.4); //başarılı
        list.InsertNode(1,6.5); //başarılı
        list.InsertNode(-2,5.5);//başarsız
        list.InsertNode(2,10.0);//başarılı
        list.DisplayList();
        list.DeleteNode(5.4);
        list.DisplayList();
        return 0;
    }

现在编辑节点部分

class Node {
public:
    int no;
    char name[15];
    char surname[15];
    int age;
    Node* next; 
};

并插入功能。流程图为here。

Node* List::InsertNode(int index, int no,char name[15],char surname[15],int age){
    if (index < 0) return NULL;
    int currIndex = 1;
    Node* currNode = head;
    while (currNode && index > currIndex) {
        currNode = currNode->next;
        currIndex++;
    }
    if (index > 0 && currNode == NULL) return NULL;
    Node* newNode = new Node;
    newNode->no = no;
    strcpy_s(newNode->name, name);
    strcpy_s(newNode->surname, surname);
    strcpy_s(newNode->age, age);
    if (index == 0) {
        newNode->next = head;
        head = newNode;
    }
    else {
        newNode->next = currNode->next;
        currNode->next = newNode;
    }
    return newNode;
}

链接列表插入和删除

4 个答案: