Question

我正在尝试进行插入排序。这首歌是一个包含Artist和Title属性的简单结构。我调用CompareTitle（Song＆amp; s1，Song＆amp; s2），如果第一首歌曲的歌曲标题在第二首歌曲的标题之前，则返回true。当代码的交换部分被注释掉时，排序条件似乎工作正常。如果没有，我收到此错误。我不知道如何处理它：

playlist.cc:192:22：错误：无法分配“Song”类型的对象，因为其隐式删除了其复制赋值运算符 * itr = j;

//do insertion sort
for(auto itr = newSongList.begin(); itr != newSongList.end(); ++itr)
{

    for(auto jtr=itr; jtr != newSongList.begin(); --jtr){
        cout << itr->GetTitle() << " " << jtr->GetTitle() << endl;
        // if s1 is not before s2 then swap them
        if(!Song::CompareTitle(*itr, *jtr)){
            cout << "Swap True (" << itr->GetTitle() << "," << jtr->GetTitle() << " )"<< endl;
            Song i = Song(itr->GetTitle(),itr->GetArtist());
            Song j = Song(jtr->GetTitle(), jtr->GetArtist());

            *itr = j;
            *jtr = i;

            cout << "Swap After (" << jtr->GetTitle() << "," << itr->GetTitle() << endl;
        }
    }
}

以下是歌曲和播放列表的结构：

#ifndef PLAYLIST_H
#define PLAYLIST_H

#include <functional>   // For std::function
#include <string>
#include <list>

using namespace std;

extern void SongCallback();

class Song {
  public:
    explicit Song(const string& title, const string& artist,
        const function<void()> = &SongCallback);
        const string& GetTitle() const;
        const string& GetArtist() const;
        bool operator==(const Song& s) const;
        bool operator()(const Song& s) const;

        static bool CompareTitle(const Song& s1, const Song& s2);
        static bool CompareArtistTitle(const Song& s1, const Song& s2);

private:
    const string title_;
    const string artist_;
    const function<void()> callback_;
};

class Playlist {
public:
    explicit Playlist() {}
    void AddSong(const string& title, const string& artist);
    unsigned int RemoveSongs(const string& title, const string& artist);
    list<Song> PlaylistSortedByTitle() const;
    list<Song> PlaylistSortedByArtistTitle() const;
    unsigned int NumSongs() const;
    unsigned int NumSongs(const string& artist) const;

private:
    list<Song> songs_;
};

#endif // PLAYLIST_H

Answer 1

似乎每次你应该交换两个元素的迭代器，而是在itr和jtr之前向容器添加元素。

for(auto itr = newSongList.begin(); itr != newSongList.end(); ++itr)
{

    for(auto jtr=itr; jtr != newSongList.begin(); --jtr){
        cout << itr->GetTitle() << " " << jtr->GetTitle() << endl;
        // if s1 is not before s2 then swap them
        if(!Song::CompareTitle(*itr, *jtr)){
            swap(*itr, *jtr);
        }
    }
}

在这里，您可以使用std::swap作为交换功能，也可以编写自己的功能来切换歌曲的标题和艺术家，以及可能添加到其中的任何其他成员。 std::iter_swap也可以作为替代。

std::swap on CPP reference

std::iter_swap on CPP reference

Answer 2

由于您拥有 const title_和artist_参数，因此无法使用assignment operator分配和覆盖这些参数。

编译器也不会生成assignment operator。由于assignment operator的目的是在构造之后更改成员，因此当永远不能更改其中一个成员时生成隐式assignment operator是没有意义的。编译器拒绝尝试猜测您希望它做什么，并强制您为自己的assignment operator提供所需的语义。

我认为，您可以使用list::insert和list::erase方法操作列表条目，就像我在下面显示的那样，以达到您想要的效果。

for(auto itr = newSongList.begin(); itr != newSongList.end(); ++itr)
{

    for(auto jtr=itr; jtr != newSongList.begin(); --jtr){
        cout << itr->GetTitle() << " " << jtr->GetTitle() << endl;
        // if s1 is not before s2 then swap them
        if(!Song::CompareTitle(*itr, *jtr)){
            cout << "Swap True (" << itr->GetTitle() << "," << jtr->GetTitle() << " )"<< endl;
            Song i = Song(itr->GetTitle(),itr->GetArtist());
            Song j = Song(jtr->GetTitle(), jtr->GetArtist());

            newSongList.insert(itr, j); // extend list by inserting j song before itr song
            newSongList.erase(itr);     // itr is still pointing to original song
            newSongList.insert(jtr, i); // extend list by inserting i song before jtr song
            newSongList.erase(jtr);     // jtr is still pointing to original song

            cout << "Swap After (" << jtr->GetTitle() << "," << itr->GetTitle() << endl;
        }
    }
}

插入排序：我做错了什么？

2 个答案: