Questions about right structure.

[SkyNetTo]

Hi everyone.
I'm tryin to create a library of my music and searching for tags in mp3 file. So good so far.

My library database is defined as

std::map<std::wstring,fileTag> m_playList;

where std::wstring is the complete path of the song and filetag is defined as:

class fileTag
{
public:
	fileTag(){};
	virtual ~fileTag(){};
	std::wstring songTitle;
	std::wstring artistName;
	std::wstring trakNumber;
	std::wstring trackYear;
	std::wstring albumName;
	std::wstring trackGenre;
};

Then I've created a function wich search all mp3's in a specific folder and create the tag map.
Everything works ok.

Now I wat to search by artist or by album. So I've created another map wich is defined as:

std::map<std::wstring,std::vector<std::map<std::wstring,fileTag>::const_iterator> > m_albumList;

std::wstring is the name of the album and the vector of const_iterators is a vector that holds all the references of the songs tha t have that albumName. (references are made in the function below)

I've made all the right reference with this function:

void CPlaylistDlg::AddAlbumToList(const std::wstring & path)
{
	std::map<std::wstring,fileTag>::iterator playListIt;
	std::map<std::wstring,std::vector<std::map<std::wstring,fileTag>::const_iterator> >::iterator it;
	

	playListIt = m_playList.find(path);
	if(playListIt != m_playList.end())
	{
		it = m_albumList.find(playListIt->second.albumName);
		if(it == m_albumList.end())
		{
			std::vector<std::map<std::wstring,fileTag>::const_iterator> m_songsVector;
			m_songsVector.push_back(playListIt);
			m_albumList[playListIt->second.albumName] = m_songsVector;
		}
		else
		{
			it->second.push_back(playListIt);
		}
	}
}

and when I want to search for an album the previous map gives me the right iterator pointing to the playList database where I can get also author, songName ecc.

My question is:
Is this the right way to do it or is there a better and faster way?

Thanks to everybody.

[Paul McKenzie]

Originally Posted by SkyNetTo

My question is:
Is this the right way to do it or is there a better and faster way?

Vector iterators can become invalid if items are added or removed from the vector. So storing vector iterators in a map seems to be a design flaw.

If it were a linked list (std::list), then you can get away with storing iterators, since std::list iterators are not invalidated unless the particular item from the list is removed.

Secondly, it would help matters if you typedefed a lot of your definitions

typedef std::map<std::wstring,fileTag> StringToFileTagMap;
StringToFileTagMap m_playList;
//...

You should do similar things with the other definitions. Not only does it make the code more readable, the definitions become much shorter and you are not wearing out your keybpard typing in a declaration of an iterator (for example).

Regards,

Paul McKenzie

[SkyNetTo]

Thanks a lot for your response.
I'm using map iterators, instead of vector iterators. Do they still become invalid if I add or remove an Item for my database?
And you're definelly right I should typedef a lot .

so my design is this:

a map (let's called it songs map) with string as key and a filetag structure as val.

a second map (let's call it albums map) with string as key (the album name) and a vector of map iterators to the songs map as val.

if I delete a song in the songs map first I should delete it referenced iterator from the vector on the albums map and if the size of the vector become zero (if this is the single songs that hase that album) delete also the pair(albumName,vector of iterator) from the albums map. Do the album map than become invalid? (I haven't tried yet deleting things only ading new songs).