无法打印双向链表

Question

我目前在尝试打印我的双向链表时遇到问题。 问题出在getSongInfo函数或printSongInfo函数中。 我对编码非常陌生，非常感谢所有帮助。 我也不知道在使用双向链表时如何使用尾指针。

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<malloc.h>
#pragma warning(disable : 4996)
#pragma warning(disable : 6387)

#pragma once

//structs 
typedef struct {
    char* title;
    char* artist;
    int rating;
    SongNode* next;
    SongNode* prev;
}SongNode;

//Constants 
#define kInfiniteLoop 1 
#define kStringLength 30

//Prototypes
int getNum(void);
void eliminateEndOfLine(char* buffer);
void printSongInfo(SongNode* head); 
SongNode* getSongInfo(SongNode** head, SongNode** tail, char title[], char artist[], int rating); 

int main() {


    char title[kStringLength];
    char artist[kStringLength];
    int rating = 0;
    SongNode* head = NULL;
    SongNode* tail = NULL;

    printf("Enter Title, Artist and Rating\n");
    printf("Enter'.' to get out of the loop and print list\n");

    while (kInfiniteLoop) {

        printf("Title: ");
        fgets(title, kStringLength, stdin);
        eliminateEndOfLine(title);

        if (strcmp(title, ".") == 0) {
            break;
        }

        printf("Artist: ");
        fgets(artist, kStringLength, stdin);
        eliminateEndOfLine(artist);

        printf("Rating: ");
        while (rating = getNum()) { // error check the rating this will check to make sure the rating is in the range 1-5.

            if (rating < 1 || rating>5) {
                printf("The number you have entered is invaild\n");
                rating = 0;
                printf("Rating: ");
                continue;
            }
            break;

            head=getSongInfo(&head, &tail, title, artist, rating); 
            printf("\n");
        }
    }
    printSongInfo(head);
    return 0;
}

  /*===============================================================================================================*/
  /*FUNCTION   :getNum(void)                                                                                       */
  /*PARAMETERS :void                                                                                               */
  /*RETURNS    :number                                                                                             */
  /*DESCRIPTION:This function is the user input function to get a number rating                                    */
  /*===============================================================================================================*/
  int getNum(void)
  {/* the array is 121 bytes in size; we'll see in a later lecture how we can improve this code */
      char record[121] = { 0 }; /* record stores the string */
      int number = 0;
      /* NOTE to student: indent and brace this function consistent with your others */
  /* use fgets() to get a string from the keyboard */
      fgets(record, 121, stdin);
      /* extract the number from the string; sscanf() returns a number
   * corresponding with the number of items it found in the string */
      if (sscanf(record, "%d", &number) != 1)
      {
          /* if the user did not enter a number recognizable by
           * the system, set number to -1 */
          number = -1;
      }
      return number;
  }
  
  
  
  /*=======================================================================================================*/
  /*FUCNTION      :void eliminateEndOfLine                                                                 */
  /*PARAMETER     :(char* buffer)                                                                          */
  /*RETURNS       :void                                                                                    */
  /*DESCRIPTION   :This function takes a pointer to a string and looks through the string to find the      */
  /*               newline.It takes the new line out of the string.                                        */
  /*=======================================================================================================*/
  void eliminateEndOfLine(char* buffer)
  {
      char* target = strchr(buffer, '\n');
      if (target != NULL)
      {
          *target = '\0';
      }
  }

  SongNode* getSongInfo(SongNode** head, SongNode** tail, char title[], char artist[], int rating)
  {
      SongNode *newBlock = NULL; 
  
      newBlock = (SongNode*)malloc(sizeof(SongNode)); 
      if (newBlock == NULL) {
          
          printf("No memory to be Allocated\n"); 
          return (*head); 
      }
  
      newBlock->title=(char*)malloc(strlen(title) + 1);
      if (newBlock->title == NULL) {
          printf("No memory can be allocated for title\n"); 
          return (*head); 
      }
  
      newBlock->artist = (char*)malloc(strlen(artist) + 1); 
      if (newBlock->rating == NULL) {
          printf("No memory can be alocated for artist\n"); 
          return (*head); 
      }
  
      newBlock->rating = (int)malloc(sizeof(int)); 
      if (newBlock->rating == NULL) {
          printf("No memory can be alllocated for rating \n"); 
          return (*head); 
      }
  
      strcpy(newBlock->title, title); 
      strcpy(newBlock->artist, artist); 
      newBlock->rating = rating; 
  
      newBlock->next = (*head); 
      newBlock->prev = NULL; 
  
      if ((*head) != NULL) 
          (*head)->prev = newBlock; 
  
      (*head) = newBlock; 
  
      return (*head); 
  }
  
  void printSongInfo(SongNode* head) {
      SongNode* ptr;
      ptr = head;
  
      printf("\n");
      printf("%-35s %-35s %-35s\n", "Title", "Artist","Rating");
  
      while (ptr != NULL) {
          printf("%-35s %-35s %-35d\n", ptr->title, ptr->artist);
          ptr = ptr->next;
      }
  }

Answer 1

您在while (rating = getnum())循环中有一个不应该存在的break语句。 它会导致循环在获取任何歌曲信息之前终止。

其他问题：

newBlock->rating = (int)malloc(sizeof(int)); 会泄漏内存，因为您分配了一些但从未释放它。 因为rating是一个int ，所以不需要为其分配内存。 （另外，请参阅我是否转换了 malloc 的结果？ ）。

getSongInfo应该要么返回新的头部，要么更新当前的头部，但不能同时更新。

更新tail类似于更新head ，但在插入 head 时不需要一直进行（有一个条件需要检查）。

在 C 源文件中不需要#pragma once 。 这应该在头文件中（并且仅在某些编译器上受支持）。