// Datentypen von Indizes:

std::map<id, Article *>            _articlesById;
std::set<Article, less_than_cheap> _articlesByPrice;

Engine::createArticle(char *title, char *descr, 
                      unsigned price, User *owner)
{	
    unsigned id = nextArticleId();
    Article *art = new Article(id, title, descr, price, owner);

    // ID-Index einfügen
    _articlesByID.insert(make_pair(id, art));

    // Index für billigste Artikel pflegen
    _articlesByPrice.insert(art);
}