C 链表错误

Question

我需要一些认真的帮助来理解 C++ 中的链表，我打算采用几周前使用数组结构编写的一个程序，并将它们转换为链表并添加几个新函数。我最担心的是我对链接列表没有信心，并且一直花时间在这里和其他网站上获取有关它们的知识。但我找不到可以帮助我解决我现在面临的问题的来源。

这是我的原始代码:

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

#define MAX 100

struct YouTubeVideo { 
char video_name[1024];        // YouTube video name
int video_ranking;            // Number of viewer hits
char video_url[1024];         // YouTube URL
};

struct YouTubeVideo Collection[MAX];

int tail = 0;

//-- Forward Declaration --// 
void printall();
void insertion();
void sort();
void branching(char option);        
void menu(); 
void load_file();
void save_file();

int main()
{
char ch; 

load_file();

printf("\n\nWelcome to CSE240: YouTube Classic Hits\n");

do {
     menu();
     fflush(stdin);                 // Flush the standard input buffer 
     ch = tolower(getchar());       // read a char, convert to lower case
     branching(ch);
} while (ch != 'q');

return 0; 
}

void menu()
{
 printf("\nMenu Options\n");
 printf("------------------------------------------------------\n");
 printf("i: Insert a new favorite\n");
 printf("p: Review your list\n"); 
 printf("q: Save and quit\n");
 printf("\n\nPlease enter a choice (i, p, or q) ---> "); 
}

void branching(char option)
{
switch(option)
{
    case 'i':
        insertion();
        sort();
    break;

    case 'p':
        printall();
    break;

    case 'q':
        save_file();
    break;

    default:
        printf("\nError: Invalid Input.  Please try again..."); 
    break;
}
}

void insertion()
{
if(tail < MAX)
{
    printf("\nWhat is the name of the video? (No spaces characters allowed)\n");
    scanf("%s", Collection[tail].video_name);

    printf("\nHow many viewer hits does this video have?\n");
    scanf("%d", &Collection[tail].video_ranking);

    printf("\nPlease enter the URL: ");
    scanf("%s", Collection[tail].video_url);

    tail++;
}
else
{
    printf("\nERROR: Your collection is full. Cannot add new entries.\n");
}
}

void sort()
{
int i = 0, j = 0; 
struct YouTubeVideo temp;

for(i = 0; i < tail; i++)
{
    for(j = i+1; j < tail; j++)
    {
        if(Collection[i].video_ranking < Collection[j].video_ranking)
        {
            temp = Collection[i];
            Collection[i] = Collection[j];
            Collection[j] = temp;
        }
    }
}

//RA: I think it's easier (and faster) to assume your current list is already
//    sorted and then insert your new element into the correct position. (You
//    can show this maintains a sorted list by induction.)

printf("\nSorting Complete...\n");
}

void printall()
{
int i; 

printf("\nCollections: \n"); 

for(i = 0; i < tail; i++)
{
    printf("\nVideo Name: %s", Collection[i].video_name);
    printf("\nRanking (Hits): %d", Collection[i].video_ranking);
    printf("\nURL: %s", Collection[i].video_url);
    printf("\n");
}
}

void save_file() { 
FILE *fileName;                                     // declare a pointer to File type 
char ch; 
int index = 0; 

fileName = fopen("ranking.dbm", "wb");              // "b" for binary mode 
                                                        // ìwî for write


if(fileName != NULL) 
{   
    fwrite(&tail, sizeof(int), 1, fileName);        // Write tail to the     file for later retrieval.

    for(index = 0; index < tail; index++)
    { 
        fwrite(&Collection[index].video_name, 1024, 1, fileName); 
        fwrite(&Collection[index].video_ranking, sizeof(int), 1, fileName);     
        fwrite(&Collection[index].video_url, 1024, 1, fileName);
    } 

    fclose(fileName);
} 
else 
    printf ("ERROR: Could not open file for saving data !\n"); 
}

void load_file() { 
FILE *fileName;                         // declare a pointer     to File type 
int index = 0; 

fileName = fopen("ranking.dbm", "rb");  // "b" for binary mode 
                                    // ìrî           for read

if(fileName != NULL) {   
    fread(&tail, sizeof(int), 1, fileName);

    for(index = 0; index < tail; index++) 
    {
        fread(Collection[index].video_name, 1024, 1, fileName);
        fread(&Collection[index].video_ranking, sizeof(int), 1, fileName);
        fread(Collection[index].video_url, 1024, 1, fileName);
    }

    fclose(fileName);
}
else 
    printf ("ERROR: Could not open file for loading data !\n"); 
}

这些是我应该做什么的确切说明:

将“YouTubeVideo”数组结构(集合)转换为链表。当条目插入链表时，程序必须对条目进行排序(按“video_name”)。 [30分](*注:如果链表未排序，您将失去10分。)

现在我已经尽我所能地尝试了，但我现在遇到了问题。

这是我尝试解决方案的代码:

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

using namespace std;

#define MAX 100

 struct YouTubeVideo
{
char name[1024];        // YouTube video name
int ranking;                // Number of viewer hits
char url[1024];             // YouTube URL
};

struct YouTubeVideo Collection[MAX];

int tail = 0;

//-- Forward Declaration --//
void printall();
void insertion();
void branching(char option);
void menu();


int main()
{
char ch;

// TODO: Add code to load save data from file

cout << "\n\nWelcome to CSE240: YouTube Classic Hits\n";

do {
    menu();
    cin >> ch; // read a char, convert to lower case
    cin.ignore();

    ch = tolower(ch);
    branching(ch);
} while (ch != 'q');

return 0;
}

void menu()
{
cout << "\nMenu Options\n";
cout << "------------------------------------------------------\n";
cout << "i: Insert a new favorite\n";
cout << "p: Review your list\n";
cout << "s: Search\n";
cout << "d: Delete an entry\n";
cout << "q: Save and quit\n";
cout << "\n\nPlease enter a choice (i, p, s, d, or q) ---> ";
}

void branching(char option)
{
switch(option)
{
    case 'i':
        insertion();
        break;

    case 'p':
        printall();
        break;

    case 's':
        // TODO: Add code to search for a particular node by name
        break;

    case 'd':
        // TODO: Add code to remove a node
        break;

    case 'q':
        // TODO: Add code to save data into a file
        break;

    default:
        cout << "\nError: Invalid Input.  Please try again...";
        break;
}
}

void insertion() { // insert a new entry
struct YouTubeVideo *p, *temp;
p = (struct YouTubeVideo *) malloc(sizeof(struct YouTubeVideo)); if (p == 0) {
    printf("out of memory\n"); return; }
printf("Enter Video name, Views, URL: \n"); scanf("%s", p->name); // p->name is array         scanf("%d", &p->phone);
scanf("%s", p->ranking);
temp = head;
if ((head == NULL)||(strcmp(p->name, temp->name) <=0)) {
    p->next = head;
    head = p;
}

else {
    while (temp->next != NULL) {
        if (stricmp(p->name, temp->next->name) <=0) { p->next = temp->next;
            temp->next = p;
            return;
        } else
            temp = temp->next; }
    p->next = NULL;
    temp->next = p;
} }

void printall()
{
int i;

cout << "\nCollections: \n";

for(i = 0; i < tail; i++)
{
    cout << "\nVideo Name: " << Collection[i].name << "\n";
    cout << "\nRanking (Hits): " << Collection[i].ranking << "\n";
    cout << "\nURL: " << Collection[i].url << "\n";
    cout << "\n";
}
}

我遇到的问题是我的插入，我收到错误未声明的标识符头，并且YouTubeVideo 中没有名为 next 的成员。我尝试在很多地方放置和声明它们，但似乎无法修复这些错误。

我真的很感谢您能给我一些帮助和任何可能的知识。我确实花了很大力气，但现在只是卡住了。

Answer 1

您需要实际实现一个链表。这看起来像是一项家庭作业，所以我想知道你对 C++ 的了解有多深。如果您还没有真正进行类和面向对象编程，那么解决此问题的最简单方法是将下一个和上一个对象添加到您的 YouTube 视频结构中。像这样:

struct YouTubeVideo {   
    char video_name[1024];        // YouTube video name  
    int video_ranking;            // Number of viewer hits 
    char video_url[1024];         // YouTube URL  
    YouTubeVideo* next;
    YouTubeVideo* previous;
};  

接下来，您需要添加头声明。这将是 YouTubeVideo* 类型。添加第一个视频时，将头部设置为指向该视频。然后，每当您添加新视频时，请将头部视频的下一个指针设置为指向新视频，并且新视频上的前一个指针应指向头部视频。这是链接列表的开始，但您的解决方案仍然非常困惑。

如果我是你，我会看看一些链表类是如何实现的。这是我编写的第一个链表类的头文件:

#ifndef LINKEDLIST_H 
#define LINKEDLIST_H

#include "List.h" 

class LinkedList : public List { 
 public: 
  LinkedList();
  virtual double get(int index) const; 
  virtual void add(double item); 
  virtual void insert(int index, double item); 
  virtual double delete_item(int index); 
  virtual int size() const;  
 private:
  class Node;
  Node* first;
  Node* last;
  int listsize;
}; 
class LinkedList::Node{
 public:
  double value;
  Node* next;
};

#endif

你可以看到这个列表中有一个Node类，这个类包含一个值double value。如果您想使用此代码，则必须使您的节点类具有一个 YouTubeVideo* 值字段。