Question

I have an album class which is designed to store and Artist Name (string), albumtitle (string) and a list of track objects (vector). I’m trying to overload the “<<” operator to enable stream-based output.

The relevant code is this:

std::ostream& Album::printTracks (std::ostream &out, std::vector<Track> &t)
{
    unsigned int i;
    for (i=0; i<t.size(); i++)
        out << " " << t.at(i);
     return out;
}
std::ostream& operator<< (std::ostream &out, Album &a)
{
    out << "Artist name: " << a.artistName << "\n" <<
        "Album Title: " << a.albumTitle << "\n" <<
        "Tracks: " << a.printTracks(out,a.getTracks());
    return out;
}

Which should print, in this order:

• The Artist’s name
• The Album Title
• The tracklist

Instead it prints this when I give it the test data:

• The tracklist
• The artist name
• The album title

“Tracks:” followed by a memory location.

Constructor for "Track Class" is:
Track::Track (std::string t, Duration* d)
    {
        title = t;
        duration = d;
    }

The code overloading “<<” in the “track” class is:

std::ostream& operator<< (std::ostream &out, Track &t)
    {
    out << "Title: " << t.title << "\n" <<
        "Duration: " << *t.duration << "\n";
    return out;
    }

And eventual code being used for output is:

Duration* d = new Duration(3,4,50); //creating duration objects for testing
Duration* d2 = new Duration(5,7,300);
Duration* d4 = new Duration(3,3,50);
Track t1 = Track("Test",d); //creating track objects
Track t2 = Track("Test2",d2);
Track t3 = Track("Test3",d4);
std::vector<Track> tracks; //forming tracks into vector
tracks.push_back(t1);
tracks.push_back(t2);
tracks.push_back(t3);
Album a = Album("Test Artist","Test Album",tracks); //create album object
cout << a << endl; // output album object

Was wondering why the ordering doesn’t print as expected?

Answer 1

It’s unspecified what order your arguments will be evaluated in. One of them has side effects (printing the tracks), so if it’s evaluated first, you’ll see those printed first.