_map_citr _map_itr _map_key2entry _size _values begin begin clear const_iterator empty end end EntryType erase erase find find HashMap insert insert iterator operator== operator[] size

empty() template<class KeyType , class MappedType , class Hash = std::hash<KeyType>, class Pred = std::equal_to<KeyType>> bool empty ( ) const 获取该 map 是否为空 获取该 map 是否为空 返回 是否为空