In C ++ 11, it is guaranteed that both the order std::multisetand the std::multimapinsertion order of elements with the same score / key are saved .
Quote from the C ++ 11 standard,
23.2.4 Associative containers
4 , . , . ; . multiset multimap , .
, (-) std::unordered_multiset std::unordered_multimap ( ) .