Why would anyone use set instead of unordered_set?

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Unordered sets have to pay for their O(1) average access time in a few ways:

  • set uses less memory than unordered_set to store the same number of elements.
  • For a small number of elements, lookups in a set might be faster than lookups in an unordered_set.
  • Even though many operations are faster in the average case for unordered_set, they are often guaranteed to have better worst case complexities for set (for example insert).
  • That set sorts the elements is useful if you want to access them in order.
  • You can lexicographically compare different sets with <, <=, > and >=. unordered_sets are not required to support these operations.

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