Add the specified key / data pair to this list. Load into the the optionally specified newFrontFlag a true value if the pair is at the front of the list, and a false value otherwise. Return 0 on success, and a non-zero value (with no effect on the list) if key is already in the list.
Declared in <bdlcc_skiplist.h>
int
addUnique(
long long const& key,
RecurringEventData const& data,
bool* newFrontFlag = 0);