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I am wondering whether this is true? If it is, is this behavior guaranteed by the c++ standard?
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The iteration order is preserved across non-distinct key values. For example, for the following multimap definition: Multimap<K, V> multimap = LinkedListMultimap. create(); multimap.
Multimap is an associative container that contains a sorted list of key-value pairs, while permitting multiple entries with the same key. Sorting is done according to the comparison function Compare , applied to the keys.
Multi-map in C++ is an associative container like map. It internally store elements in key value pair. But unlike map which store only unique keys, multimap can have duplicate keys.
No. It's called "unordered" for a reason. If you need to maintain an order of insertion, you've chosen an unsuitable data structure.
The elements in a std::map must have unique keys, so... no.
The std::multimap container allows multiple values mapped to one key. When iterating over a std::multimap the elements are ordered by key, but the order of elements having the same key is not specified.
Note that in the latest draft of the forthcoming C++0x standard (N3092), the relative ordering of elements with the same key is guaranteed (so, at some point, you'll be able to rely on this behavior).
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