Question

我需要帮助将*user_playlist指向播放列表节点。我怎么能这样做？

struct playlist_ {
  int album;
  int track_num;
  struct playlist_ *next;
};
typedef struct playlist_  playlists;

struct users_ {
  int user_ID;
  playlists *user_playlist;
  struct users_ *next;
};
typedef struct users_ users;

p_users = (users *)malloc(sizeof(users *));
p_users -> user_ID = account_number;
head_users = p_users;
head_users -> next = NULL;
users_pointer = head_users;

p_playlists = (playlists *)malloc(sizeof(playlists));
curr_playlists = p_playlists;
curr_playlists -> album = NULL;
curr_playlists -> track_num = NULL;
curr_playlists -> next = NULL;
curr_users -> user_playlist = curr_playlists;

 users *head_users,*curr_users,*p_users,*users_pointer;
 playlists *head_playlists,*curr_playlists,*p_playlists,*playlist_pointer;

Answer 1

这是一个问题：

p_users = (users *)malloc(sizeof(users *));

它只分配指针的大小，而不是users结构的大小。改为：

p_users = malloc(sizeof(users));

或：

p_users = malloc(sizeof(*p_users));

Casting the return value of malloc() is unnecessary and potentially dangerous.

编辑：

取消引用unitialised或NULL指针将导致分段错误。这声明但不初始化 curr_users（对于列出的其他变量也是如此）：

users *head_users,*curr_users,*p_users,*users_pointer;

然后尝试访问curr_users：

curr_users->user_playlist = curr_playlists; /* Segmentation fault. */

在使用之前初始化curr_users，有效users结构或NULL并在引用之前检查非null：

users *head_users = NULL,*curr_users = NULL,
    *p_users = NULL,*users_pointer = NULL;

if (curr_users)
{
    curr_users->user_playlist = curr_playlists;
}

如何将一个结构指向另一个结构

1 个答案: