c++ - STL 列表迭代器错误

Question

我必须使用 STL 为我的数据结构类实现我自己的列表，这里是我的代码。

播放列表.h

#ifndef PLAYLIST_H
#define PLAYLIST_H

#include <iostream>
using std::ostream;

#include <list>
using std::list;

class Song;

class Playlist
{
public:
    void append(const char* name, const char* artist);
    list<Song>::iterator find(const char* name) const;
    void delete_song(const char* name);
    void print(ostream& out) const;

private:
    list<Song> plist;
};

ostream& operator << (ostream& out, const Playlist& playlist);

#endif  /* PLAYLIST_H */


ostream& operator << (ostream& out, const Playlist& playlist);

#endif  /* PLAYLIST_H */

播放列表.cpp

#include <iostream>
using std::ostream;
using std::endl;

#include <cstring>

#include "Song.h"
#include "Playlist.h"

void Playlist::append(const char* name, const char* artist)
{
    Song song(name, artist);
    plist.push_back(song);
}

list<Song>::iterator Playlist::find(const char* name) const
{
    list<Song>::iterator itr = plist.begin(); // error occurs here
    while(itr != plist.end() && strcmp(itr->get_name(), name) == 0)
    {
        itr++;
    } 

    return itr;
}

void Playlist::delete_song(const char* name)
{
    list<Song>::iterator itr = find(name);
    if (itr != plist.end())
        plist.erase(itr);
}

void Playlist::print(ostream& out) const
{
    list<Song>::iterator itr = plist.begin(); // error occurs here
    while (itr != plist.end())
    {
       out << *itr << endl;
       itr++;
    }
} 

ostream& operator << (ostream& out, const Playlist& playlist)
{
    playlist.print(out);
    return out;
}

当我尝试编译它时，我得到:

错误:请求从‘std::list::const_iterator {aka std::_List_const_iterator}’到非标量类型‘std::list::iterator {aka std::_List_iterator}’的转换

在代码中标记的两个地方。

Answer 1

方法 void Playlist::print(ostream& out) const 被指定为常量。因此 plist 是 const，所以 plist.begin() 返回一个 const_iterator。您要么必须从方法中删除 const，要么使用 const_cast(最差解决方案)，要么简单地使用 const_iterator 迭代列表(最佳选择)。