Question

所以我试图找出一个类的程序，我需要模拟一个播放列表，可以在音乐库中添加和删除歌曲，在播放列表中添加和删除歌曲等。

我有一个Song类和一个播放列表类，一个矢量库（用于歌曲库），以及一个包含vecto songList的矢量播放列表。如果我想从库中删除一首歌并在库矢量中给出一个歌曲指针的索引，我该如何检查该“歌曲”是否在任何“播放列表”中？这是我的相关代码部分：

    using namespace std;

    class Song {
    public:
         Song(string title, string line, int count) {
              name = title;
              firstLine = line;
              playCount = count;
         }
         string GetName() {
              return name;
         }

         string GetFirstLine() {
              return firstLine;
         }
    private:
         string name;
         string firstLine;
         int playCount;;
    };

    class Playlist {
    public:
         Playlist(string name = "none"){
              pName = name;
         }
         void AddSong(Song* song) {
              songPtr.push_back(song);
         }
         void RemoveSong(int songIndex) {
              songPtr.erase(songPtr.begin() + songIndex);
         }
         string GetSongAtIndex(int index) {
              return (songPtr.at(index))->GetName();
         }

    private:
         string pName;
         vector<Song*> songPtr;
    };

    int main() {
    string userIn;
    vector<Song*> library;
    vector<Playlist> playlists;

    // code for adding songs to library using "new"
    // code for adding songs to playlist using "new"


    // delete song from library
    // first, list songs in library
        size = library.size();
        for (i = 0; i < size; i++) {
            cout << "  " << i << ": " << (library.at(i))->GetName();
            cout << endl;
        }
        // have user pick wich song they want erased
        cout << "Pick a song index number: ";
        cin.clear();
        cin >> sIndex;

        // FIXME: check if song is in any playlist, and if it is, remove it
        string songName = (library.at(sIndex))->GetName();
        int size = playlists.size(); //remove song from playlists
        for (i = 0; i < size; i++) {
            int size2 = (playlists.at(i)).GetPSize();
            for (j = 0; j < size2; j++) {
                string tempName = (playlists.at(j)).GetSongAtIndex(j);
                if (tempName == songName) {
                    (playlists.at(i)).RemoveSong(j);
                }
            }
        }
        // code to delete song from library and free the memory

我有什么不起作用，当我在删除它后尝试列出库中的歌曲时，它会给我一个“超出范围”的错误并导致程序崩溃。当我评论出关于在播放列表中找到它的部分时，它从库中删除就好了。只有当我尝试检查该歌曲是否在播放列表中时才会出现错误。我对编程比较陌生，所以很可能我错过了一些东西，但我不知道如何解决这个问题。

Answer 1

如果从播放列表中删除元素，则不应增加索引并减小大小：

// check if song is in any playlist, and if it is, remove it
string songName = library.at(sIndex)->GetName();
int size = playlists.size(); //remove song from playlists
for (j = 0; j < size2; ) {                // do not increment j here
    string tempName = playlists.at(i).GetSongAtIndex(j); // i, not j for playlists.at()
    if (tempName == songName) {
        playlists.at(i).RemoveSong(j);  // j remains the same
        --size2;                          // one element less
    } else {
        ++j;                              // increment here
    }
}

如何使用类的成员搜索对象指针的向量？

1 个答案: