In C++ does std::multiset keep a stable sorting order?

Question

Suppose I have two items, a and b, that compare the same. So a < b is false, and b < a is false. If these items are inserted into a std::multiset (or std::multimap) as keys, do I have any guarantees of their final sorted order?

I've checked a couple of references, but I couldn't find the answer. I'm tempted to think that there are no guarantees and that it's left up to each particular implementation.

Thanks.

Possible duplicate of [Does std::multiset guarantee insertion order?](https://stackoverflow.com/questions/2643473/does-stdmultiset-guarantee-insertion-order) — underscore_d, Aug 03 '17 at 14:40

Mark Ransom · Accepted Answer · 2017-03-08T05:09:28.453

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This thread implies that it is not guaranteed by the current standard but is met by all known current implementations, and gives a link to the C++0x draft standard that includes a guarantee.

edited Mar 08 '17 at 05:09

answered Feb 09 '09 at 23:19

Mark Ransom

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For the record, the C++0x guarantee is "insert at upper bound." – Drew Dormann Feb 09 '09 at 23:36
Awesome. We aren't using C++11 yet, but I'm going to be adding a unit test to our test suite to ensure the compiler's behavior across the versions we use. – mskfisher May 25 '11 at 18:13
@katta dang, that was the most aggressively nasty site I've ever browsed to. I'll fix the link ASAP. – Mark Ransom Mar 08 '17 at 05:06

In C++ does std::multiset keep a stable sorting order?

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