Does std::sort change the relative order of equal elements?

Question

Does the standard guarantee that order of equal elements will not change (eh, forgot the term for that) by using std::sort or do I need to consider an alternative solution to achieve this goal?

Answer 1

std::sort is not guaranteed to be stable (the term you were trying to think of). As you'd guess, std::stable_sort is guaranteed to be stable. std::stable_sort also provides a guarantee on worst-case complexity, which std::sort does not. std::sort is typically faster on average though.

Answer 2

From C++ reference: here

Elements that would compare equal to each other are not guaranteed to keep their original relative order.

You might want stable_sort, but note that it's not as fast (in average)