1

私は立ち往生していて、なぜセグメンテーション違反が発生するのか理解できません。プレイリストに最初の追加を追加すると、すべて問題ありません。次に、プレイリストを印刷してからプレイリストに追加しようとすると、セグメンテーション違反が発生します。gdbはここでエラーを報告していますif( (curr_playlist -> album) == NULL && (curr_playlist -> track_num) == NULL){。誰かが私が問題を見つけるのを手伝ってもらえますか?印刷機能はリンクリストを変更していますか?

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

struct users_ {
  int user_ID;
  struct playlist_ *playlist;
  struct users_ *next;
};
typedef struct users_ users;

/*This is how I created the user list*/

fscanf(transaction_file,"%d\n",&account_number);

      /*Checks for empty list, if true creates the first user*/
      if( head_users == NULL){
        p_users = malloc(sizeof(users ));
        p_users -> user_ID = account_number;
        head_users = p_users;
        curr_users = p_users;
        head_users -> next = NULL;
        users_pointer = head_users;

      /*If list is not empty create new user and puts it in front of list*/
      }else{
        p_users = malloc(sizeof(users));
        p_users -> user_ID = account_number;
        curr_users = p_users;
        curr_users -> next = head_users;
        head_users = curr_users;
        users_pointer = head_users;
      }

      /*Create an empty playlist for user and set everything to null, empty playlist*/
        p_playlists = malloc(sizeof(playlists));
        curr_playlists = p_playlists;
        curr_playlists -> album = FALSE;
        curr_playlists -> track_num = FALSE;
        curr_playlists -> next = NULL;
        curr_users -> playlist = p_playlists;

int add_playlist(users *user_pointer,album *all_albums,int user_ID,int album_ID,int track_num){

  playlists *head_playlist,*tail_playlist,*curr_playlist,*p_playlist;
  users *curr_users;

  curr_users = user_pointer;
  while(curr_users){

    /* Find this user in link list */
    if(curr_users -> user_ID == user_ID){
      curr_playlist = curr_users -> playlist;

      /* Check if playlist is empty for this user if so, update the empty list*/
      if( (curr_playlist -> album) == NULL && (curr_playlist -> track_num) == NULL){
        tail_playlist = curr_users -> playlist;
        curr_playlist -> album = album_ID;
        curr_playlist -> track_num = track_num;
        curr_playlist -> next = NULL;

      }else{

        /*Creates a new playlist node with the request album and track number*/
        p_playlist = (playlists *)malloc(sizeof(playlists ));
        p_playlist -> album = album_ID;
        p_playlist -> track_num = track_num;
        p_playlist -> next = NULL;

        /*Traverse Playlist, find the tail node*/
        curr_playlist = curr_users -> playlist;
        while(curr_playlist ){
          tail_playlist = curr_playlist;
          curr_playlist = curr_playlist -> next;
        }

        /* Adds the new playlist at the end */
          tail_playlist -> next = p_playlist;
      }

    }
    curr_users = curr_users -> next;
  }
  /*Updates the playlist hits for each new playlist node*/
  *all_albums[album_ID].playlist_hits[track_num] = *all_albums[album_ID].playlist_hits[track_num] + 1;
}

int print_account(album *all_albums,int account_number,users *user_pointer){
  users *curr_users;
  playlists *curr_playlist;

  int i;
  curr_users = user_pointer;

  /*Check playlist for each user if NULL, playlist is empty*/
  while (curr_users){
    if(curr_users -> user_ID == account_number){

      printf("ACCOUNT %d\n",curr_users->user_ID);
      if(curr_users -> playlist -> album == -100 && curr_users -> playlist -> track_num == -100){
        printf("  EMPTY Playlist\n");

      }else{
        /*Goes through the user playlist and prints out the information*/
        for(curr_playlist = curr_users -> playlist; curr_playlist; curr_playlist = curr_playlist -> next){
          printf("  ALBUM %d:  %s\n",curr_users -> playlist -> album,
                 all_albums[curr_users -> playlist -> album].tracks[curr_users -> playlist -> track_num]);
          curr_users -> playlist = curr_users -> playlist -> next;
        }
      }
    }
      curr_users = curr_users -> next;
  }
}
4

1 に答える 1

2

curr_users -> playlist問題の一部は、「空の」プレイリストへのポインタで初期化された仮定である可能性があります。NULLであるか、初期化されていない値がある場合album、後続のステートメントでチェックされると、セグメンテーション違反が発生します。コードはユーザーリストが最初に作成される方法を示していないので、少し推測しています。

ユーザーリストが最初に「空の」プレイリストエントリで作成されていない場合、playlistメンバーはNULLに初期化され、次のステートメントが必要です。

     if ( (curr_playlist -> album) == NULL && (curr_playlist -> track_num) == NULL )

代わりに次のようになります。

if ( curr_playlist == NULL )

malloc次に、else部分と同様の新しいプレイリストを(経由で)割り当てる必要があります。(もちろん、ifブロックとブロックの両方elseがプレイリスト構造を割り当てて初期化するモジュール性の問題があります)。

于 2012-04-06T00:00:55.147 に答える