24 Containers library [containers]

24.6 Container adaptors [container.adaptors]

24.6.12 Class template flat_multiset [flat.multiset]

24.6.12.3 Constructors [flat.multiset.cons]

explicit flat_multiset(container_type cont, const key_compare& comp = key_compare());
Effects: Initializes c with std​::​move(cont) and compare with comp, and sorts the range [begin(), end()) with respect to compare.
Complexity: Linear in N if cont is already sorted with respect to compare and otherwise , where N is the value of cont.size() before this call.