The following compiles OK typedef string Colour; struct edge_properties   {     vector < set< Colour > > eColours;   } until I get to   template < typename Graph >     void populate_arrow_maps(const Graph & g)   {   typename graph_traits<Graph>::edge_iterator edge_iter, edges_end;   typedef vector > VCS;   typedef vector >::iterator vcs_iter, vcs_end;   for (tie(edge_iter, edges_end) = edges(g); edge_iter != edges_end; ++edge_iter) {                 VCS & vcolour_set = get(m_eColours_map, *edge_iter);                 for(vcs_iter = vcolour_set.begin(); vcs_iter != vcolour_set.end(); ++vcs_iter) {                   ;                 }         }   } Then compiler says error: expected unqualified id before '=' token Referring to the line which is underlined above. So its referring to vcs_iter. Whats wrong? Thanks