Erase element from <set>

[Edward01]

Hello, I am having a problem erasing elemnet from set. I'm getting 11 errors which send me to "xstddef standard header". I have no idea what have i done wrong with it.

  class Song{
public:
	enum eSection{ INTRO, VERSE, CHORUS, TRANSITION };
	enum eSectionDurationInSeconds{ INTRO_DUR = 5, VERSE_DUR = 10, CHORUS_DUR = 20, TRANSITION_DUR = 5 };

	Song(){  m_songName = "Not Set Yet"; m_singerName = "Not Set Yet"; m_composerName  = "Not Set Yet"; } //Default Constructor
	Song(string songName, string composerName, string singerName);//Constructor
	~Song();//Destructor
	void set(); // ?
	string getSongName();
	void addSection(const eSection sec, const eSectionDurationInSeconds iDuration);
	const void playSong() const;// Function Plays the Song.
	bool operator == (const Song& s) const;
	void operator()(const int& sec);
	const double getSongLenghtInMinutes() const;
private:
	string m_songName; // Song Name.
	string m_composerName; // Song Composer
	string m_singerName; // The singer, could be more than one.
	vector<pair<eSection,eSectionDurationInSeconds>> m_songStructure;
};

#ifndef RadioStation_h
#define RadioStation_h
#include"Song.h"
#include"Playlist.h"
#include<vector>
#include<set>

class RadioStation{
private:
	vector<Playlist> m_RadioPlayList;
	set<Song> m_Db;
	int m_numOfLists;
	double m_totalListsTime;
public:
	enum{MAX_PLAYLIST_LEN_IN_MINUTES = 12};
	RadioStation() { m_numOfLists = 0; m_totalListsTime = 0; }
	~RadioStation();
	//bool isRadioListEmpty() { if( m_numOfLists==0 ) return true; else false; }
	void addSongToDB(const Song& newsong);
	void removeSongFromDB(const Song& song);
	void addPlaylist(const Playlist& pl);
	void removePlaylist(unsigned int iPlaylistNumber);
	void playAllPlaylists();
};

i saw erase from set on this site, but it didnt work for me.
this part doesnt work..

void RadioStation::removeSongFromDB(const Song& song){
	m_Db.erase(song);
}

I also tried to use iterators, but it did't work either.

[Peter87]

std::set uses operator< by default so if you have not overloaded operator< for Song you will get an error because of that.

[Catfish4]

std::set requires a "less than" function (operator) to be available.

In your case, you must carefully overload operator< for Song.

bool operator < (const Song &s) const
{
    if (m_songName != s.m_songName)
        return m_songName < s.m_songName;
    else
    if ( /* composer */ )
        return /* ... */ ;
    else
    if ( /* singer name */ )
        return /* ... */ ;
    else
        return m_songStructure < s.m_songStructure;
}

Of course, the else branches aren't needed because return quits the function altogether -- they're just there to clarify the intent.