Does an iterator iterate through boost::unordered_set or boost::unordered_map in the same order as long as the set's unchanged?

Question

Does an iterator iterate through boost::unordered_set or boost::unordered_map in the same order as long as the set or the map is unchanged?

score 5 · Accepted Answer · answered Oct 04 '12 at 14:59

Some implementations of a hash map will reorder the items that hash to the same bin, putting the most recently accessed item at the front of a list, as an optimization. This would change the order. I'm not aware that boost::unordered_map does this, but in the future you might end up substituting std::unordered_map and it will all depend on your compiler's implementation.

score 1 · Answer 2 · answered Oct 04 '12 at 14:41

1

It should be deterministic but as long as they are so-called unordered, you should not rely on this to iterate over your elements.

answered Oct 04 '12 at 14:41

mister why

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Does an iterator iterate through boost::unordered_set or boost::unordered_map in the same order as long as the set's unchanged?

2 Answers2