Hi, I like to build a data structure and like to access it with different keys, so I try multi_index for this. My data structure looks like this: struct learnedMeasure { // target_name + measure_name together is the composite key std::string target_name; std::string measure_name; float negative; float positive; float zero; } I like to access this data structure like this in SQL: SELECT measure, Negative, Positive, Zero from tabelle WHERE target_name='xxx' SELECT Target_name, Negative, Positive, Zero from tabelle WHERE measure_name='xxx' SELECT Negative,Positive,Zero from tabelle WHERE measure_name='xxx' AND Target_name='yyy' I hacked the basic example to get this working. My example compiles, but if I execute it, I get only warnings: probe: /usr/include/boost/multi_index/detail/index_iterator.hpp:107: typename Node::value_type& boost::multi_index::detail::index_iterator<Node, Container>::operator*() const [with Node = Container>boost::multi_index::detail::ordered_index_node<boost:: multi_index::detail::index_node_base<learnedMeasure> Container>>, Container = Container>>boost::multi_index::detail::ordered_index<boost:: multi_index::composite_key<learnedMeasure, Container>>boost::multi_index::member<learnedMeasure, std::string, Container>>&learnedMeasure::measu .... more warnings I put my example code online. Perhaps someone could take a look in it and help me to find this problem. http://cpp.sourceforge.net/?show=9550 regards Andreas