c - 如何动态分配结构数组？

Question

我如何为轨道动态分配结构数组，以便我可以使用 all_albums_p[i] 访问它？我需要 all_albums_p[i] 可以访问它，因为我要返回 all_albums_p。

struct tracks_{
  char tracks_title;
  int playlist_hits;
};

struct album_ {
  int num_tracks;
  struct tracks_ tracks;
};

typedef struct album_ album;
typedef struct tracks_ tracks;

album *all_albums_p = (album *)malloc(sizeof(album)*number_of_album);

******** 我有什么已更改********

struct tracks_{
      char *tracks_title;
      int *playlist_hits;
    };

Answer 1

现在，您的每个专辑都有一个轨道，轨道名称应该是一个字符，而不是您可能想要的字符数组。

您已经正确分配了您的专辑，但您还需要分配每张专辑的轨道。

执行此操作的最简单方法是仅指定固定数量的轨道作为最大值，并确保您的其他代码不超过该数量。

const int MAX_TRACKS = 20;
const int MAX_HITS = 20;
const int MAX_TRACK_NAME_LENGTH = 63;

struct track_{
    char tracks_title[MAX_TRACK_NAME_LENGTH+1];
    int playlist_hits[MAX_HITS];
    int playlist_hits_count;
};

struct album_ {
    int num_tracks;
    struct track_ tracks[MAX_TRACKS];
};

或者，如果手头有相关信息，您可以动态分配轨道和轨道名称以达到所需的确切大小。例如，假设您只是复制现有的相册数组:

struct track_ {
    char *track_title;
    int *playlist_hits;
    int playlist_hits_count;
};

struct album_ {
    int num_tracks;
    struct track_ *tracks;
};

typedef struct album_ album;
typedef struct track_ track;

album *copy_albums(album *all_albums_p, int number_of_album) {
    album *all_albums_copy = (album *)malloc(sizeof(album) * number_of_album);

    // copy each album
    for (int album_i = 0; album_i < number_of_album; album_i++) {
        album * current_album = all_albums_p + album_i;
        album * copy_album = all_albums_copy + album_i;

        copy_album->num_tracks = current_album->num_tracks;
        copy_album->tracks = (track *)malloc(sizeof(track) * current_album->num_tracks);

        // copy each track, and it's hits, and make a new copy of it's name
        for (int track_i = 0; track_i < current_album->num_tracks; track_i++) {
            track * current_track = current_album->tracks + track_i;
            track * copy_track = copy_album->tracks + track_i;

            copy_track->playlist_hits_count = current_track->playlist_hits_count;
            copy_track->playlist_hits = (int *)malloc(sizeof(int) * current_track->playlist_hits_count);
            memcpy(copy_track->playlist_hits, current_track->playlist_hits, current_track->playlist_hits_count * sizeof(int));

            copy_track->track_title = _strdup(current_track->track_title);
        }
    }

    return all_albums_copy;
}