Question

I have no idea why this is happening, I followed the example posted here.

class Song {

private:
    // singletong
    Song();
    Song(Song const&); // don't implement
    void operator = (Song const&); //don't implement

public:
    // Singleton method
    static Song &getInstance(){
        static Song song;
        return song;
    }

};

If I don’t call the class, there’s no problem. As soon as I call the Song class like this:

Song::getInstance();
// also tried: Song &song = Song::getInstance();

Xcode doesn’t want to build the project anymore. I’m getting this error:

Any ideas why this is happening?

Answer 1

Your not implementing the constructor which has to exist since your instantiating an object in the getInstance() function:

static Song song;

Either implement it inline (unprefered):

private:
    // singletong
    Song() {
        // Your implementation goes here
    }

Or implement it in a compilation unit (e.g Sound.cpp) (prefered):

Song::Song(){
    // Your implementation goes here
}