How to write file using model plugin?

edit

Using coding as following:

public:

void Load(physics::ModelPtr _parent, sdf::ElementPtr _sdf) {
    this->model = _parent;
    this->updateConnection = event::Events::ConnectWorldUpdateBegin(
            boost::bind(&ModelPluginTutorial::OnUpdate, this, _1));     
    std::ofstream file("Angle.txt");
    for (int i = 0; i < N; i++) {
        file << position[i] << std::endl;
    }
    file.close();
}

However things turned out unexpected,there are no file generated.who can help me out of this problem?