using a singleton when you will need more than one instance

hi,
i'd like to use a singleton for one of my classes. The class has an attribute named oid and i will need one instance for every value of oid - i just need to make sure there is no second one.
so i tried:

Code:

---

class cAnlagenArt {
public:
	static cAnlagenArt* self( QString oid );
private:
	static QMap<QString, cAnlagenArt* > _self;
}

---

and tried the following:

Code:

---

cAnlagenArt* cAnlagenArt::self(QString oid) {
    if ( ! _self.contains(oid) )
        _self[oid] = new cAnlagenArt( oid );
    return _self[oid];
}

---

which gets me lots of
undefined reference to `cAnlagenArt::_self'

how else can i do this?

Have you defined the static member somewhere in the .cpp file?

Code:

---

QMap<QString, cAnlagenArt* > cAnlagenArt::_self;

---

noo, i thought i only needed to set pointers to 0 in this way. thank you